[{"data":1,"prerenderedAt":3046},["ShallowReactive",2],{"doc-\u002Flearn\u002Finstance-vs-class-variables-in-python":3},{"id":4,"title":5,"body":6,"description":3039,"extension":3040,"meta":3041,"navigation":124,"path":3042,"seo":3043,"stem":3044,"__hash__":3045},"content\u002Flearn\u002Finstance-vs-class-variables-in-python.md","Instance vs Class Variables in Python",{"type":7,"value":8,"toc":3017},"minimark",[9,13,26,44,47,61,66,299,304,328,336,340,354,358,364,382,385,537,541,554,557,574,577,632,636,650,654,660,663,665,813,817,834,836,852,855,866,878,882,885,899,902,932,934,1160,1164,1171,1174,1183,1186,1188,1254,1258,1267,1278,1281,1367,1371,1385,1388,1408,1415,1419,1422,1425,1436,1438,1620,1623,1627,1630,1632,1646,1648,1809,1815,1819,1822,1833,1836,1839,2002,2006,2029,2032,2035,2189,2193,2211,2218,2222,2225,2284,2287,2404,2408,2427,2430,2448,2451,2562,2566,2583,2587,2601,2605,2608,2632,2636,2639,2729,2732,2763,2765,2891,2895,2927,2930,2942,2946,2951,2954,2958,2961,2965,2968,2972,2975,2979,3013],[10,11,5],"h1",{"id":12},"instance-vs-class-variables-in-python",[14,15,16,17,21,22,25],"p",{},"In Python classes, ",[18,19,20],"strong",{},"instance variables"," and ",[18,23,24],{},"class variables"," are used for different kinds of data.",[27,28,29,37],"ul",{},[30,31,32,33,36],"li",{},"Use an ",[18,34,35],{},"instance variable"," for data that belongs to one object",[30,38,39,40,43],{},"Use a ",[18,41,42],{},"class variable"," for data shared by all objects of the class",[14,45,46],{},"This page explains:",[27,48,49,52,55,58],{},[30,50,51],{},"what each one means",[30,53,54],{},"when each one is created",[30,56,57],{},"how Python finds them",[30,59,60],{},"common beginner mistakes",[62,63,65],"h2",{"id":64},"quick-example","Quick example",[67,68,73],"pre",{"className":69,"code":70,"language":71,"meta":72,"style":72},"language-python shiki shiki-themes material-theme-lighter github-light github-dark","class Dog:\n    species = \"Canis familiaris\"  # class variable\n\n    def __init__(self, name):\n        self.name = name            # instance variable\n\n\na = Dog(\"Max\")\nb = Dog(\"Bella\")\n\nprint(a.species)\nprint(b.species)\nprint(a.name)\nprint(b.name)\n","python","",[74,75,76,93,119,126,153,176,181,186,209,230,235,253,269,284],"code",{"__ignoreMap":72},[77,78,81,85,89],"span",{"class":79,"line":80},"line",1,[77,82,84],{"class":83},"sbsja","class",[77,86,88],{"class":87},"sbgvK"," Dog",[77,90,92],{"class":91},"sP7_E",":\n",[77,94,96,100,104,108,112,115],{"class":79,"line":95},2,[77,97,99],{"class":98},"su5hD","    species ",[77,101,103],{"class":102},"smGrS","=",[77,105,107],{"class":106},"sjJ54"," \"",[77,109,111],{"class":110},"s_sjI","Canis familiaris",[77,113,114],{"class":106},"\"",[77,116,118],{"class":117},"sutJx","  # class variable\n",[77,120,122],{"class":79,"line":121},3,[77,123,125],{"emptyLinePlaceholder":124},true,"\n",[77,127,129,132,136,139,143,146,150],{"class":79,"line":128},4,[77,130,131],{"class":83},"    def",[77,133,135],{"class":134},"sptTA"," __init__",[77,137,138],{"class":91},"(",[77,140,142],{"class":141},"smCYv","self",[77,144,145],{"class":91},",",[77,147,149],{"class":148},"sFwrP"," name",[77,151,152],{"class":91},"):\n",[77,154,156,160,163,167,170,173],{"class":79,"line":155},5,[77,157,159],{"class":158},"s_hVV","        self",[77,161,162],{"class":91},".",[77,164,166],{"class":165},"skxfh","name",[77,168,169],{"class":102}," =",[77,171,172],{"class":98}," name            ",[77,174,175],{"class":117},"# instance variable\n",[77,177,179],{"class":79,"line":178},6,[77,180,125],{"emptyLinePlaceholder":124},[77,182,184],{"class":79,"line":183},7,[77,185,125],{"emptyLinePlaceholder":124},[77,187,189,192,194,197,199,201,204,206],{"class":79,"line":188},8,[77,190,191],{"class":98},"a ",[77,193,103],{"class":102},[77,195,88],{"class":196},"slqww",[77,198,138],{"class":91},[77,200,114],{"class":106},[77,202,203],{"class":110},"Max",[77,205,114],{"class":106},[77,207,208],{"class":91},")\n",[77,210,212,215,217,219,221,223,226,228],{"class":79,"line":211},9,[77,213,214],{"class":98},"b ",[77,216,103],{"class":102},[77,218,88],{"class":196},[77,220,138],{"class":91},[77,222,114],{"class":106},[77,224,225],{"class":110},"Bella",[77,227,114],{"class":106},[77,229,208],{"class":91},[77,231,233],{"class":79,"line":232},10,[77,234,125],{"emptyLinePlaceholder":124},[77,236,238,241,243,246,248,251],{"class":79,"line":237},11,[77,239,240],{"class":134},"print",[77,242,138],{"class":91},[77,244,245],{"class":196},"a",[77,247,162],{"class":91},[77,249,250],{"class":165},"species",[77,252,208],{"class":91},[77,254,256,258,260,263,265,267],{"class":79,"line":255},12,[77,257,240],{"class":134},[77,259,138],{"class":91},[77,261,262],{"class":196},"b",[77,264,162],{"class":91},[77,266,250],{"class":165},[77,268,208],{"class":91},[77,270,272,274,276,278,280,282],{"class":79,"line":271},13,[77,273,240],{"class":134},[77,275,138],{"class":91},[77,277,245],{"class":196},[77,279,162],{"class":91},[77,281,166],{"class":165},[77,283,208],{"class":91},[77,285,287,289,291,293,295,297],{"class":79,"line":286},14,[77,288,240],{"class":134},[77,290,138],{"class":91},[77,292,262],{"class":196},[77,294,162],{"class":91},[77,296,166],{"class":165},[77,298,208],{"class":91},[14,300,301],{},[18,302,303],{},"Output:",[67,305,307],{"className":69,"code":306,"language":71,"meta":72,"style":72},"Canis familiaris\nCanis familiaris\nMax\nBella\n",[74,308,309,314,318,323],{"__ignoreMap":72},[77,310,311],{"class":79,"line":80},[77,312,313],{"class":98},"Canis familiaris\n",[77,315,316],{"class":79,"line":95},[77,317,313],{"class":98},[77,319,320],{"class":79,"line":121},[77,321,322],{"class":98},"Max\n",[77,324,325],{"class":79,"line":128},[77,326,327],{"class":98},"Bella\n",[14,329,39,330,332,333,335],{},[18,331,42],{}," for shared data. Use an ",[18,334,35],{}," for data that should be different for each object.",[62,337,339],{"id":338},"what-this-page-teaches","What this page teaches",[27,341,342,345,348,351],{},[30,343,344],{},"What instance variables are",[30,346,347],{},"What class variables are",[30,349,350],{},"How they are different",[30,352,353],{},"How to choose the right one",[62,355,357],{"id":356},"what-is-an-instance-variable","What is an instance variable?",[14,359,360,361,363],{},"An ",[18,362,35],{}," belongs to one object.",[14,365,366,367,370,371,374,375,162],{},"It is usually created with ",[74,368,369],{},"self.variable_name"," inside ",[74,372,373],{},"__init__",". If you are new to this, see ",[245,376,378,379,381],{"href":377},"\u002Flearn\u002Fthe-__init__-method-in-python-explained\u002F","the ",[74,380,373],{}," method in Python explained",[14,383,384],{},"Example:",[67,386,388],{"className":69,"code":387,"language":71,"meta":72,"style":72},"class Dog:\n    def __init__(self, name, age):\n        self.name = name\n        self.age = age\n\n\ndog1 = Dog(\"Max\", 5)\ndog2 = Dog(\"Bella\", 3)\n\nprint(dog1.name)\nprint(dog2.name)\n",[74,389,390,398,419,432,446,450,454,479,503,507,522],{"__ignoreMap":72},[77,391,392,394,396],{"class":79,"line":80},[77,393,84],{"class":83},[77,395,88],{"class":87},[77,397,92],{"class":91},[77,399,400,402,404,406,408,410,412,414,417],{"class":79,"line":95},[77,401,131],{"class":83},[77,403,135],{"class":134},[77,405,138],{"class":91},[77,407,142],{"class":141},[77,409,145],{"class":91},[77,411,149],{"class":148},[77,413,145],{"class":91},[77,415,416],{"class":148}," age",[77,418,152],{"class":91},[77,420,421,423,425,427,429],{"class":79,"line":121},[77,422,159],{"class":158},[77,424,162],{"class":91},[77,426,166],{"class":165},[77,428,169],{"class":102},[77,430,431],{"class":98}," name\n",[77,433,434,436,438,441,443],{"class":79,"line":128},[77,435,159],{"class":158},[77,437,162],{"class":91},[77,439,440],{"class":165},"age",[77,442,169],{"class":102},[77,444,445],{"class":98}," age\n",[77,447,448],{"class":79,"line":155},[77,449,125],{"emptyLinePlaceholder":124},[77,451,452],{"class":79,"line":178},[77,453,125],{"emptyLinePlaceholder":124},[77,455,456,459,461,463,465,467,469,471,473,477],{"class":79,"line":183},[77,457,458],{"class":98},"dog1 ",[77,460,103],{"class":102},[77,462,88],{"class":196},[77,464,138],{"class":91},[77,466,114],{"class":106},[77,468,203],{"class":110},[77,470,114],{"class":106},[77,472,145],{"class":91},[77,474,476],{"class":475},"srdBf"," 5",[77,478,208],{"class":91},[77,480,481,484,486,488,490,492,494,496,498,501],{"class":79,"line":188},[77,482,483],{"class":98},"dog2 ",[77,485,103],{"class":102},[77,487,88],{"class":196},[77,489,138],{"class":91},[77,491,114],{"class":106},[77,493,225],{"class":110},[77,495,114],{"class":106},[77,497,145],{"class":91},[77,499,500],{"class":475}," 3",[77,502,208],{"class":91},[77,504,505],{"class":79,"line":211},[77,506,125],{"emptyLinePlaceholder":124},[77,508,509,511,513,516,518,520],{"class":79,"line":232},[77,510,240],{"class":134},[77,512,138],{"class":91},[77,514,515],{"class":196},"dog1",[77,517,162],{"class":91},[77,519,166],{"class":165},[77,521,208],{"class":91},[77,523,524,526,528,531,533,535],{"class":79,"line":237},[77,525,240],{"class":134},[77,527,138],{"class":91},[77,529,530],{"class":196},"dog2",[77,532,162],{"class":91},[77,534,166],{"class":165},[77,536,208],{"class":91},[14,538,539],{},[18,540,303],{},[67,542,544],{"className":69,"code":543,"language":71,"meta":72,"style":72},"Max\nBella\n",[74,545,546,550],{"__ignoreMap":72},[77,547,548],{"class":79,"line":80},[77,549,322],{"class":98},[77,551,552],{"class":79,"line":95},[77,553,327],{"class":98},[14,555,556],{},"Here:",[27,558,559,565,571],{},[30,560,561,564],{},[74,562,563],{},"self.name"," is an instance variable",[30,566,567,570],{},[74,568,569],{},"self.age"," is also an instance variable",[30,572,573],{},"each object gets its own values",[14,575,576],{},"If you change one object's instance variable, the other objects do not change.",[67,578,580],{"className":69,"code":579,"language":71,"meta":72,"style":72},"dog1.name = \"Rocky\"\n\nprint(dog1.name)\nprint(dog2.name)\n",[74,581,582,600,604,618],{"__ignoreMap":72},[77,583,584,586,588,590,592,594,597],{"class":79,"line":80},[77,585,515],{"class":98},[77,587,162],{"class":91},[77,589,166],{"class":165},[77,591,169],{"class":102},[77,593,107],{"class":106},[77,595,596],{"class":110},"Rocky",[77,598,599],{"class":106},"\"\n",[77,601,602],{"class":79,"line":95},[77,603,125],{"emptyLinePlaceholder":124},[77,605,606,608,610,612,614,616],{"class":79,"line":121},[77,607,240],{"class":134},[77,609,138],{"class":91},[77,611,515],{"class":196},[77,613,162],{"class":91},[77,615,166],{"class":165},[77,617,208],{"class":91},[77,619,620,622,624,626,628,630],{"class":79,"line":128},[77,621,240],{"class":134},[77,623,138],{"class":91},[77,625,530],{"class":196},[77,627,162],{"class":91},[77,629,166],{"class":165},[77,631,208],{"class":91},[14,633,634],{},[18,635,303],{},[67,637,639],{"className":69,"code":638,"language":71,"meta":72,"style":72},"Rocky\nBella\n",[74,640,641,646],{"__ignoreMap":72},[77,642,643],{"class":79,"line":80},[77,644,645],{"class":98},"Rocky\n",[77,647,648],{"class":79,"line":95},[77,649,327],{"class":98},[62,651,653],{"id":652},"what-is-a-class-variable","What is a class variable?",[14,655,656,657,659],{},"A ",[18,658,42],{}," belongs to the class itself.",[14,661,662],{},"It is defined inside the class, but outside methods.",[14,664,384],{},[67,666,668],{"className":69,"code":667,"language":71,"meta":72,"style":72},"class Dog:\n    species = \"Canis familiaris\"\n\n    def __init__(self, name):\n        self.name = name\n\n\ndog1 = Dog(\"Max\")\ndog2 = Dog(\"Bella\")\n\nprint(Dog.species)\nprint(dog1.species)\nprint(dog2.species)\n",[74,669,670,678,690,694,710,722,726,730,748,766,770,785,799],{"__ignoreMap":72},[77,671,672,674,676],{"class":79,"line":80},[77,673,84],{"class":83},[77,675,88],{"class":87},[77,677,92],{"class":91},[77,679,680,682,684,686,688],{"class":79,"line":95},[77,681,99],{"class":98},[77,683,103],{"class":102},[77,685,107],{"class":106},[77,687,111],{"class":110},[77,689,599],{"class":106},[77,691,692],{"class":79,"line":121},[77,693,125],{"emptyLinePlaceholder":124},[77,695,696,698,700,702,704,706,708],{"class":79,"line":128},[77,697,131],{"class":83},[77,699,135],{"class":134},[77,701,138],{"class":91},[77,703,142],{"class":141},[77,705,145],{"class":91},[77,707,149],{"class":148},[77,709,152],{"class":91},[77,711,712,714,716,718,720],{"class":79,"line":155},[77,713,159],{"class":158},[77,715,162],{"class":91},[77,717,166],{"class":165},[77,719,169],{"class":102},[77,721,431],{"class":98},[77,723,724],{"class":79,"line":178},[77,725,125],{"emptyLinePlaceholder":124},[77,727,728],{"class":79,"line":183},[77,729,125],{"emptyLinePlaceholder":124},[77,731,732,734,736,738,740,742,744,746],{"class":79,"line":188},[77,733,458],{"class":98},[77,735,103],{"class":102},[77,737,88],{"class":196},[77,739,138],{"class":91},[77,741,114],{"class":106},[77,743,203],{"class":110},[77,745,114],{"class":106},[77,747,208],{"class":91},[77,749,750,752,754,756,758,760,762,764],{"class":79,"line":211},[77,751,483],{"class":98},[77,753,103],{"class":102},[77,755,88],{"class":196},[77,757,138],{"class":91},[77,759,114],{"class":106},[77,761,225],{"class":110},[77,763,114],{"class":106},[77,765,208],{"class":91},[77,767,768],{"class":79,"line":232},[77,769,125],{"emptyLinePlaceholder":124},[77,771,772,774,776,779,781,783],{"class":79,"line":237},[77,773,240],{"class":134},[77,775,138],{"class":91},[77,777,778],{"class":196},"Dog",[77,780,162],{"class":91},[77,782,250],{"class":165},[77,784,208],{"class":91},[77,786,787,789,791,793,795,797],{"class":79,"line":255},[77,788,240],{"class":134},[77,790,138],{"class":91},[77,792,515],{"class":196},[77,794,162],{"class":91},[77,796,250],{"class":165},[77,798,208],{"class":91},[77,800,801,803,805,807,809,811],{"class":79,"line":271},[77,802,240],{"class":134},[77,804,138],{"class":91},[77,806,530],{"class":196},[77,808,162],{"class":91},[77,810,250],{"class":165},[77,812,208],{"class":91},[14,814,815],{},[18,816,303],{},[67,818,820],{"className":69,"code":819,"language":71,"meta":72,"style":72},"Canis familiaris\nCanis familiaris\nCanis familiaris\n",[74,821,822,826,830],{"__ignoreMap":72},[77,823,824],{"class":79,"line":80},[77,825,313],{"class":98},[77,827,828],{"class":79,"line":95},[77,829,313],{"class":98},[77,831,832],{"class":79,"line":121},[77,833,313],{"class":98},[14,835,556],{},[27,837,838,843,849],{},[30,839,840,842],{},[74,841,250],{}," is a class variable",[30,844,845,846,848],{},"it is shared by all ",[74,847,778],{}," objects",[30,850,851],{},"both objects can read it",[14,853,854],{},"Class variables are useful for:",[27,856,857,860,863],{},[30,858,859],{},"constants",[30,861,862],{},"shared settings",[30,864,865],{},"values that should be the same for every object",[14,867,868,869,873,874,162],{},"If you need a refresher on classes and objects, see ",[245,870,872],{"href":871},"\u002Flearn\u002Fpython-classes-and-objects-explained\u002F","Python classes and objects explained"," or ",[245,875,877],{"href":876},"\u002Fglossary\u002Fwhat-is-a-class-in-python\u002F","what is a class in Python",[62,879,881],{"id":880},"main-difference-at-a-glance","Main difference at a glance",[14,883,884],{},"The difference is simple:",[27,886,887,893],{},[30,888,889,892],{},[18,890,891],{},"Instance variable",": one value per object",[30,894,895,898],{},[18,896,897],{},"Class variable",": one shared value on the class",[14,900,901],{},"Typical uses:",[27,903,904,918],{},[30,905,906,907,909,910,909,912,909,915],{},"instance variables: ",[74,908,166],{},", ",[74,911,440],{},[74,913,914],{},"price",[74,916,917],{},"file_path",[30,919,920,921,909,923,909,926,909,929],{},"class variables: ",[74,922,250],{},[74,924,925],{},"app_name",[74,927,928],{},"tax_rate",[74,930,931],{},"counter",[14,933,384],{},[67,935,937],{"className":69,"code":936,"language":71,"meta":72,"style":72},"class Product:\n    store_name = \"Python Shop\"   # class variable\n\n    def __init__(self, name, price):\n        self.name = name         # instance variable\n        self.price = price       # instance variable\n\n\np1 = Product(\"Keyboard\", 50)\np2 = Product(\"Mouse\", 25)\n\nprint(p1.store_name)\nprint(p2.store_name)\nprint(p1.name, p1.price)\nprint(p2.name, p2.price)\n",[74,938,939,948,965,969,990,1005,1020,1024,1028,1053,1078,1082,1098,1113,1136],{"__ignoreMap":72},[77,940,941,943,946],{"class":79,"line":80},[77,942,84],{"class":83},[77,944,945],{"class":87}," Product",[77,947,92],{"class":91},[77,949,950,953,955,957,960,962],{"class":79,"line":95},[77,951,952],{"class":98},"    store_name ",[77,954,103],{"class":102},[77,956,107],{"class":106},[77,958,959],{"class":110},"Python Shop",[77,961,114],{"class":106},[77,963,964],{"class":117},"   # class variable\n",[77,966,967],{"class":79,"line":121},[77,968,125],{"emptyLinePlaceholder":124},[77,970,971,973,975,977,979,981,983,985,988],{"class":79,"line":128},[77,972,131],{"class":83},[77,974,135],{"class":134},[77,976,138],{"class":91},[77,978,142],{"class":141},[77,980,145],{"class":91},[77,982,149],{"class":148},[77,984,145],{"class":91},[77,986,987],{"class":148}," price",[77,989,152],{"class":91},[77,991,992,994,996,998,1000,1003],{"class":79,"line":155},[77,993,159],{"class":158},[77,995,162],{"class":91},[77,997,166],{"class":165},[77,999,169],{"class":102},[77,1001,1002],{"class":98}," name         ",[77,1004,175],{"class":117},[77,1006,1007,1009,1011,1013,1015,1018],{"class":79,"line":178},[77,1008,159],{"class":158},[77,1010,162],{"class":91},[77,1012,914],{"class":165},[77,1014,169],{"class":102},[77,1016,1017],{"class":98}," price       ",[77,1019,175],{"class":117},[77,1021,1022],{"class":79,"line":183},[77,1023,125],{"emptyLinePlaceholder":124},[77,1025,1026],{"class":79,"line":188},[77,1027,125],{"emptyLinePlaceholder":124},[77,1029,1030,1033,1035,1037,1039,1041,1044,1046,1048,1051],{"class":79,"line":211},[77,1031,1032],{"class":98},"p1 ",[77,1034,103],{"class":102},[77,1036,945],{"class":196},[77,1038,138],{"class":91},[77,1040,114],{"class":106},[77,1042,1043],{"class":110},"Keyboard",[77,1045,114],{"class":106},[77,1047,145],{"class":91},[77,1049,1050],{"class":475}," 50",[77,1052,208],{"class":91},[77,1054,1055,1058,1060,1062,1064,1066,1069,1071,1073,1076],{"class":79,"line":232},[77,1056,1057],{"class":98},"p2 ",[77,1059,103],{"class":102},[77,1061,945],{"class":196},[77,1063,138],{"class":91},[77,1065,114],{"class":106},[77,1067,1068],{"class":110},"Mouse",[77,1070,114],{"class":106},[77,1072,145],{"class":91},[77,1074,1075],{"class":475}," 25",[77,1077,208],{"class":91},[77,1079,1080],{"class":79,"line":237},[77,1081,125],{"emptyLinePlaceholder":124},[77,1083,1084,1086,1088,1091,1093,1096],{"class":79,"line":255},[77,1085,240],{"class":134},[77,1087,138],{"class":91},[77,1089,1090],{"class":196},"p1",[77,1092,162],{"class":91},[77,1094,1095],{"class":165},"store_name",[77,1097,208],{"class":91},[77,1099,1100,1102,1104,1107,1109,1111],{"class":79,"line":271},[77,1101,240],{"class":134},[77,1103,138],{"class":91},[77,1105,1106],{"class":196},"p2",[77,1108,162],{"class":91},[77,1110,1095],{"class":165},[77,1112,208],{"class":91},[77,1114,1115,1117,1119,1121,1123,1125,1127,1130,1132,1134],{"class":79,"line":286},[77,1116,240],{"class":134},[77,1118,138],{"class":91},[77,1120,1090],{"class":196},[77,1122,162],{"class":91},[77,1124,166],{"class":165},[77,1126,145],{"class":91},[77,1128,1129],{"class":196}," p1",[77,1131,162],{"class":91},[77,1133,914],{"class":165},[77,1135,208],{"class":91},[77,1137,1139,1141,1143,1145,1147,1149,1151,1154,1156,1158],{"class":79,"line":1138},15,[77,1140,240],{"class":134},[77,1142,138],{"class":91},[77,1144,1106],{"class":196},[77,1146,162],{"class":91},[77,1148,166],{"class":165},[77,1150,145],{"class":91},[77,1152,1153],{"class":196}," p2",[77,1155,162],{"class":91},[77,1157,914],{"class":165},[77,1159,208],{"class":91},[62,1161,1163],{"id":1162},"how-python-looks-up-variables","How Python looks up variables",[14,1165,1166,1167,1170],{},"When you write ",[74,1168,1169],{},"obj.variable_name",", Python does not only check the object.",[14,1172,1173],{},"Python looks in this order:",[1175,1176,1177,1180],"ol",{},[30,1178,1179],{},"first, it checks the object for an instance variable",[30,1181,1182],{},"if it does not find one, it checks the class",[14,1184,1185],{},"This is why objects can read class variables.",[14,1187,384],{},[67,1189,1191],{"className":69,"code":1190,"language":71,"meta":72,"style":72},"class Example:\n    value = 100  # class variable\n\n\nobj = Example()\n\nprint(obj.value)\n",[74,1192,1193,1202,1214,1218,1222,1234,1238],{"__ignoreMap":72},[77,1194,1195,1197,1200],{"class":79,"line":80},[77,1196,84],{"class":83},[77,1198,1199],{"class":87}," Example",[77,1201,92],{"class":91},[77,1203,1204,1207,1209,1212],{"class":79,"line":95},[77,1205,1206],{"class":98},"    value ",[77,1208,103],{"class":102},[77,1210,1211],{"class":475}," 100",[77,1213,118],{"class":117},[77,1215,1216],{"class":79,"line":121},[77,1217,125],{"emptyLinePlaceholder":124},[77,1219,1220],{"class":79,"line":128},[77,1221,125],{"emptyLinePlaceholder":124},[77,1223,1224,1227,1229,1231],{"class":79,"line":155},[77,1225,1226],{"class":98},"obj ",[77,1228,103],{"class":102},[77,1230,1199],{"class":196},[77,1232,1233],{"class":91},"()\n",[77,1235,1236],{"class":79,"line":178},[77,1237,125],{"emptyLinePlaceholder":124},[77,1239,1240,1242,1244,1247,1249,1252],{"class":79,"line":183},[77,1241,240],{"class":134},[77,1243,138],{"class":91},[77,1245,1246],{"class":196},"obj",[77,1248,162],{"class":91},[77,1250,1251],{"class":165},"value",[77,1253,208],{"class":91},[14,1255,1256],{},[18,1257,303],{},[67,1259,1261],{"className":69,"code":1260,"language":71,"meta":72,"style":72},"100\n",[74,1262,1263],{"__ignoreMap":72},[77,1264,1265],{"class":79,"line":80},[77,1266,1260],{"class":475},[14,1268,1269,1271,1272,1274,1275,1277],{},[74,1270,1246],{}," does not have its own ",[74,1273,1251],{},", so Python gets ",[74,1276,1251],{}," from the class.",[14,1279,1280],{},"Now look at this:",[67,1282,1284],{"className":69,"code":1283,"language":71,"meta":72,"style":72},"class Example:\n    value = 100\n\n\nobj = Example()\nobj.value = 200\n\nprint(obj.value)\nprint(Example.value)\n",[74,1285,1286,1294,1303,1307,1311,1321,1334,1338,1352],{"__ignoreMap":72},[77,1287,1288,1290,1292],{"class":79,"line":80},[77,1289,84],{"class":83},[77,1291,1199],{"class":87},[77,1293,92],{"class":91},[77,1295,1296,1298,1300],{"class":79,"line":95},[77,1297,1206],{"class":98},[77,1299,103],{"class":102},[77,1301,1302],{"class":475}," 100\n",[77,1304,1305],{"class":79,"line":121},[77,1306,125],{"emptyLinePlaceholder":124},[77,1308,1309],{"class":79,"line":128},[77,1310,125],{"emptyLinePlaceholder":124},[77,1312,1313,1315,1317,1319],{"class":79,"line":155},[77,1314,1226],{"class":98},[77,1316,103],{"class":102},[77,1318,1199],{"class":196},[77,1320,1233],{"class":91},[77,1322,1323,1325,1327,1329,1331],{"class":79,"line":178},[77,1324,1246],{"class":98},[77,1326,162],{"class":91},[77,1328,1251],{"class":165},[77,1330,169],{"class":102},[77,1332,1333],{"class":475}," 200\n",[77,1335,1336],{"class":79,"line":183},[77,1337,125],{"emptyLinePlaceholder":124},[77,1339,1340,1342,1344,1346,1348,1350],{"class":79,"line":188},[77,1341,240],{"class":134},[77,1343,138],{"class":91},[77,1345,1246],{"class":196},[77,1347,162],{"class":91},[77,1349,1251],{"class":165},[77,1351,208],{"class":91},[77,1353,1354,1356,1358,1361,1363,1365],{"class":79,"line":211},[77,1355,240],{"class":134},[77,1357,138],{"class":91},[77,1359,1360],{"class":196},"Example",[77,1362,162],{"class":91},[77,1364,1251],{"class":165},[77,1366,208],{"class":91},[14,1368,1369],{},[18,1370,303],{},[67,1372,1374],{"className":69,"code":1373,"language":71,"meta":72,"style":72},"200\n100\n",[74,1375,1376,1381],{"__ignoreMap":72},[77,1377,1378],{"class":79,"line":80},[77,1379,1380],{"class":475},"200\n",[77,1382,1383],{"class":79,"line":95},[77,1384,1260],{"class":475},[14,1386,1387],{},"What happened?",[27,1389,1390,1398,1405],{},[30,1391,1392,1395,1396],{},[74,1393,1394],{},"obj.value = 200"," created an ",[18,1397,35],{},[30,1399,1400,1401,1404],{},"it did ",[18,1402,1403],{},"not"," change the class variable",[30,1406,1407],{},"the instance variable now hides the class variable for that object",[14,1409,1410,1411,162],{},"This idea becomes easier once you are comfortable with ",[245,1412,1414],{"href":1413},"\u002Fglossary\u002Fwhat-is-an-object-in-python\u002F","what is an object in Python",[62,1416,1418],{"id":1417},"when-to-use-instance-variables","When to use instance variables",[14,1420,1421],{},"Use instance variables when each object should store its own data.",[14,1423,1424],{},"Good examples:",[27,1426,1427,1429,1431,1433],{},[30,1428,166],{},[30,1430,440],{},[30,1432,914],{},[30,1434,1435],{},"file path",[14,1437,384],{},[67,1439,1441],{"className":69,"code":1440,"language":71,"meta":72,"style":72},"class User:\n    def __init__(self, username, email):\n        self.username = username\n        self.email = email\n\n\nu1 = User(\"anna\", \"anna@example.com\")\nu2 = User(\"ben\", \"ben@example.com\")\n\nprint(u1.username, u1.email)\nprint(u2.username, u2.email)\n",[74,1442,1443,1452,1474,1488,1502,1506,1510,1539,1568,1572,1596],{"__ignoreMap":72},[77,1444,1445,1447,1450],{"class":79,"line":80},[77,1446,84],{"class":83},[77,1448,1449],{"class":87}," User",[77,1451,92],{"class":91},[77,1453,1454,1456,1458,1460,1462,1464,1467,1469,1472],{"class":79,"line":95},[77,1455,131],{"class":83},[77,1457,135],{"class":134},[77,1459,138],{"class":91},[77,1461,142],{"class":141},[77,1463,145],{"class":91},[77,1465,1466],{"class":148}," username",[77,1468,145],{"class":91},[77,1470,1471],{"class":148}," email",[77,1473,152],{"class":91},[77,1475,1476,1478,1480,1483,1485],{"class":79,"line":121},[77,1477,159],{"class":158},[77,1479,162],{"class":91},[77,1481,1482],{"class":165},"username",[77,1484,169],{"class":102},[77,1486,1487],{"class":98}," username\n",[77,1489,1490,1492,1494,1497,1499],{"class":79,"line":128},[77,1491,159],{"class":158},[77,1493,162],{"class":91},[77,1495,1496],{"class":165},"email",[77,1498,169],{"class":102},[77,1500,1501],{"class":98}," email\n",[77,1503,1504],{"class":79,"line":155},[77,1505,125],{"emptyLinePlaceholder":124},[77,1507,1508],{"class":79,"line":178},[77,1509,125],{"emptyLinePlaceholder":124},[77,1511,1512,1515,1517,1519,1521,1523,1526,1528,1530,1532,1535,1537],{"class":79,"line":183},[77,1513,1514],{"class":98},"u1 ",[77,1516,103],{"class":102},[77,1518,1449],{"class":196},[77,1520,138],{"class":91},[77,1522,114],{"class":106},[77,1524,1525],{"class":110},"anna",[77,1527,114],{"class":106},[77,1529,145],{"class":91},[77,1531,107],{"class":106},[77,1533,1534],{"class":110},"anna@example.com",[77,1536,114],{"class":106},[77,1538,208],{"class":91},[77,1540,1541,1544,1546,1548,1550,1552,1555,1557,1559,1561,1564,1566],{"class":79,"line":188},[77,1542,1543],{"class":98},"u2 ",[77,1545,103],{"class":102},[77,1547,1449],{"class":196},[77,1549,138],{"class":91},[77,1551,114],{"class":106},[77,1553,1554],{"class":110},"ben",[77,1556,114],{"class":106},[77,1558,145],{"class":91},[77,1560,107],{"class":106},[77,1562,1563],{"class":110},"ben@example.com",[77,1565,114],{"class":106},[77,1567,208],{"class":91},[77,1569,1570],{"class":79,"line":211},[77,1571,125],{"emptyLinePlaceholder":124},[77,1573,1574,1576,1578,1581,1583,1585,1587,1590,1592,1594],{"class":79,"line":232},[77,1575,240],{"class":134},[77,1577,138],{"class":91},[77,1579,1580],{"class":196},"u1",[77,1582,162],{"class":91},[77,1584,1482],{"class":165},[77,1586,145],{"class":91},[77,1588,1589],{"class":196}," u1",[77,1591,162],{"class":91},[77,1593,1496],{"class":165},[77,1595,208],{"class":91},[77,1597,1598,1600,1602,1605,1607,1609,1611,1614,1616,1618],{"class":79,"line":237},[77,1599,240],{"class":134},[77,1601,138],{"class":91},[77,1603,1604],{"class":196},"u2",[77,1606,162],{"class":91},[77,1608,1482],{"class":165},[77,1610,145],{"class":91},[77,1612,1613],{"class":196}," u2",[77,1615,162],{"class":91},[77,1617,1496],{"class":165},[77,1619,208],{"class":91},[14,1621,1622],{},"This is the best choice for values that are different from one object to another.",[62,1624,1626],{"id":1625},"when-to-use-class-variables","When to use class variables",[14,1628,1629],{},"Use class variables when the value should be shared.",[14,1631,1424],{},[27,1633,1634,1637,1640,1643],{},[30,1635,1636],{},"default tax rate",[30,1638,1639],{},"app name",[30,1641,1642],{},"category",[30,1644,1645],{},"object counter",[14,1647,384],{},[67,1649,1651],{"className":69,"code":1650,"language":71,"meta":72,"style":72},"class Account:\n    bank_name = \"Python Bank\"\n\n    def __init__(self, owner):\n        self.owner = owner\n\n\na1 = Account(\"Ava\")\na2 = Account(\"Noah\")\n\nprint(Account.bank_name)\nprint(a1.bank_name)\nprint(a2.bank_name)\n",[74,1652,1653,1662,1676,1680,1697,1711,1715,1719,1739,1759,1763,1779,1794],{"__ignoreMap":72},[77,1654,1655,1657,1660],{"class":79,"line":80},[77,1656,84],{"class":83},[77,1658,1659],{"class":87}," Account",[77,1661,92],{"class":91},[77,1663,1664,1667,1669,1671,1674],{"class":79,"line":95},[77,1665,1666],{"class":98},"    bank_name ",[77,1668,103],{"class":102},[77,1670,107],{"class":106},[77,1672,1673],{"class":110},"Python Bank",[77,1675,599],{"class":106},[77,1677,1678],{"class":79,"line":121},[77,1679,125],{"emptyLinePlaceholder":124},[77,1681,1682,1684,1686,1688,1690,1692,1695],{"class":79,"line":128},[77,1683,131],{"class":83},[77,1685,135],{"class":134},[77,1687,138],{"class":91},[77,1689,142],{"class":141},[77,1691,145],{"class":91},[77,1693,1694],{"class":148}," owner",[77,1696,152],{"class":91},[77,1698,1699,1701,1703,1706,1708],{"class":79,"line":155},[77,1700,159],{"class":158},[77,1702,162],{"class":91},[77,1704,1705],{"class":165},"owner",[77,1707,169],{"class":102},[77,1709,1710],{"class":98}," owner\n",[77,1712,1713],{"class":79,"line":178},[77,1714,125],{"emptyLinePlaceholder":124},[77,1716,1717],{"class":79,"line":183},[77,1718,125],{"emptyLinePlaceholder":124},[77,1720,1721,1724,1726,1728,1730,1732,1735,1737],{"class":79,"line":188},[77,1722,1723],{"class":98},"a1 ",[77,1725,103],{"class":102},[77,1727,1659],{"class":196},[77,1729,138],{"class":91},[77,1731,114],{"class":106},[77,1733,1734],{"class":110},"Ava",[77,1736,114],{"class":106},[77,1738,208],{"class":91},[77,1740,1741,1744,1746,1748,1750,1752,1755,1757],{"class":79,"line":211},[77,1742,1743],{"class":98},"a2 ",[77,1745,103],{"class":102},[77,1747,1659],{"class":196},[77,1749,138],{"class":91},[77,1751,114],{"class":106},[77,1753,1754],{"class":110},"Noah",[77,1756,114],{"class":106},[77,1758,208],{"class":91},[77,1760,1761],{"class":79,"line":232},[77,1762,125],{"emptyLinePlaceholder":124},[77,1764,1765,1767,1769,1772,1774,1777],{"class":79,"line":237},[77,1766,240],{"class":134},[77,1768,138],{"class":91},[77,1770,1771],{"class":196},"Account",[77,1773,162],{"class":91},[77,1775,1776],{"class":165},"bank_name",[77,1778,208],{"class":91},[77,1780,1781,1783,1785,1788,1790,1792],{"class":79,"line":255},[77,1782,240],{"class":134},[77,1784,138],{"class":91},[77,1786,1787],{"class":196},"a1",[77,1789,162],{"class":91},[77,1791,1776],{"class":165},[77,1793,208],{"class":91},[77,1795,1796,1798,1800,1803,1805,1807],{"class":79,"line":271},[77,1797,240],{"class":134},[77,1799,138],{"class":91},[77,1801,1802],{"class":196},"a2",[77,1804,162],{"class":91},[77,1806,1776],{"class":165},[77,1808,208],{"class":91},[14,1810,1811,1812,1814],{},"If the data should be different for each object, do ",[18,1813,1403],{}," use a class variable.",[62,1816,1818],{"id":1817},"common-beginner-mistake-mutable-class-variables","Common beginner mistake: mutable class variables",[14,1820,1821],{},"Be careful with mutable values like:",[27,1823,1824,1827,1830],{},[30,1825,1826],{},"lists",[30,1828,1829],{},"dictionaries",[30,1831,1832],{},"sets",[14,1834,1835],{},"If you put one of these in a class variable, all objects share the same value.",[14,1837,1838],{},"Example of the problem:",[67,1840,1842],{"className":69,"code":1841,"language":71,"meta":72,"style":72},"class Student:\n    grades = []  # class variable\n\n    def __init__(self, name):\n        self.name = name\n\n\ns1 = Student(\"Ava\")\ns2 = Student(\"Noah\")\n\ns1.grades.append(95)\n\nprint(s1.grades)\nprint(s2.grades)\n",[74,1843,1844,1853,1865,1869,1885,1897,1901,1905,1924,1943,1947,1969,1973,1987],{"__ignoreMap":72},[77,1845,1846,1848,1851],{"class":79,"line":80},[77,1847,84],{"class":83},[77,1849,1850],{"class":87}," Student",[77,1852,92],{"class":91},[77,1854,1855,1858,1860,1863],{"class":79,"line":95},[77,1856,1857],{"class":98},"    grades ",[77,1859,103],{"class":102},[77,1861,1862],{"class":91}," []",[77,1864,118],{"class":117},[77,1866,1867],{"class":79,"line":121},[77,1868,125],{"emptyLinePlaceholder":124},[77,1870,1871,1873,1875,1877,1879,1881,1883],{"class":79,"line":128},[77,1872,131],{"class":83},[77,1874,135],{"class":134},[77,1876,138],{"class":91},[77,1878,142],{"class":141},[77,1880,145],{"class":91},[77,1882,149],{"class":148},[77,1884,152],{"class":91},[77,1886,1887,1889,1891,1893,1895],{"class":79,"line":155},[77,1888,159],{"class":158},[77,1890,162],{"class":91},[77,1892,166],{"class":165},[77,1894,169],{"class":102},[77,1896,431],{"class":98},[77,1898,1899],{"class":79,"line":178},[77,1900,125],{"emptyLinePlaceholder":124},[77,1902,1903],{"class":79,"line":183},[77,1904,125],{"emptyLinePlaceholder":124},[77,1906,1907,1910,1912,1914,1916,1918,1920,1922],{"class":79,"line":188},[77,1908,1909],{"class":98},"s1 ",[77,1911,103],{"class":102},[77,1913,1850],{"class":196},[77,1915,138],{"class":91},[77,1917,114],{"class":106},[77,1919,1734],{"class":110},[77,1921,114],{"class":106},[77,1923,208],{"class":91},[77,1925,1926,1929,1931,1933,1935,1937,1939,1941],{"class":79,"line":211},[77,1927,1928],{"class":98},"s2 ",[77,1930,103],{"class":102},[77,1932,1850],{"class":196},[77,1934,138],{"class":91},[77,1936,114],{"class":106},[77,1938,1754],{"class":110},[77,1940,114],{"class":106},[77,1942,208],{"class":91},[77,1944,1945],{"class":79,"line":232},[77,1946,125],{"emptyLinePlaceholder":124},[77,1948,1949,1952,1954,1957,1959,1962,1964,1967],{"class":79,"line":237},[77,1950,1951],{"class":98},"s1",[77,1953,162],{"class":91},[77,1955,1956],{"class":165},"grades",[77,1958,162],{"class":91},[77,1960,1961],{"class":196},"append",[77,1963,138],{"class":91},[77,1965,1966],{"class":475},"95",[77,1968,208],{"class":91},[77,1970,1971],{"class":79,"line":255},[77,1972,125],{"emptyLinePlaceholder":124},[77,1974,1975,1977,1979,1981,1983,1985],{"class":79,"line":271},[77,1976,240],{"class":134},[77,1978,138],{"class":91},[77,1980,1951],{"class":196},[77,1982,162],{"class":91},[77,1984,1956],{"class":165},[77,1986,208],{"class":91},[77,1988,1989,1991,1993,1996,1998,2000],{"class":79,"line":286},[77,1990,240],{"class":134},[77,1992,138],{"class":91},[77,1994,1995],{"class":196},"s2",[77,1997,162],{"class":91},[77,1999,1956],{"class":165},[77,2001,208],{"class":91},[14,2003,2004],{},[18,2005,303],{},[67,2007,2009],{"className":69,"code":2008,"language":71,"meta":72,"style":72},"[95]\n[95]\n",[74,2010,2011,2021],{"__ignoreMap":72},[77,2012,2013,2016,2018],{"class":79,"line":80},[77,2014,2015],{"class":91},"[",[77,2017,1966],{"class":475},[77,2019,2020],{"class":91},"]\n",[77,2022,2023,2025,2027],{"class":79,"line":95},[77,2024,2015],{"class":91},[77,2026,1966],{"class":475},[77,2028,2020],{"class":91},[14,2030,2031],{},"Both objects show the same list because there is only one shared class variable.",[14,2033,2034],{},"If each object should have its own list, create it as an instance variable instead:",[67,2036,2038],{"className":69,"code":2037,"language":71,"meta":72,"style":72},"class Student:\n    def __init__(self, name):\n        self.name = name\n        self.grades = []  # instance variable\n\n\ns1 = Student(\"Ava\")\ns2 = Student(\"Noah\")\n\ns1.grades.append(95)\n\nprint(s1.grades)\nprint(s2.grades)\n",[74,2039,2040,2048,2064,2076,2091,2095,2099,2117,2135,2139,2157,2161,2175],{"__ignoreMap":72},[77,2041,2042,2044,2046],{"class":79,"line":80},[77,2043,84],{"class":83},[77,2045,1850],{"class":87},[77,2047,92],{"class":91},[77,2049,2050,2052,2054,2056,2058,2060,2062],{"class":79,"line":95},[77,2051,131],{"class":83},[77,2053,135],{"class":134},[77,2055,138],{"class":91},[77,2057,142],{"class":141},[77,2059,145],{"class":91},[77,2061,149],{"class":148},[77,2063,152],{"class":91},[77,2065,2066,2068,2070,2072,2074],{"class":79,"line":121},[77,2067,159],{"class":158},[77,2069,162],{"class":91},[77,2071,166],{"class":165},[77,2073,169],{"class":102},[77,2075,431],{"class":98},[77,2077,2078,2080,2082,2084,2086,2088],{"class":79,"line":128},[77,2079,159],{"class":158},[77,2081,162],{"class":91},[77,2083,1956],{"class":165},[77,2085,169],{"class":102},[77,2087,1862],{"class":91},[77,2089,2090],{"class":117},"  # instance variable\n",[77,2092,2093],{"class":79,"line":155},[77,2094,125],{"emptyLinePlaceholder":124},[77,2096,2097],{"class":79,"line":178},[77,2098,125],{"emptyLinePlaceholder":124},[77,2100,2101,2103,2105,2107,2109,2111,2113,2115],{"class":79,"line":183},[77,2102,1909],{"class":98},[77,2104,103],{"class":102},[77,2106,1850],{"class":196},[77,2108,138],{"class":91},[77,2110,114],{"class":106},[77,2112,1734],{"class":110},[77,2114,114],{"class":106},[77,2116,208],{"class":91},[77,2118,2119,2121,2123,2125,2127,2129,2131,2133],{"class":79,"line":188},[77,2120,1928],{"class":98},[77,2122,103],{"class":102},[77,2124,1850],{"class":196},[77,2126,138],{"class":91},[77,2128,114],{"class":106},[77,2130,1754],{"class":110},[77,2132,114],{"class":106},[77,2134,208],{"class":91},[77,2136,2137],{"class":79,"line":211},[77,2138,125],{"emptyLinePlaceholder":124},[77,2140,2141,2143,2145,2147,2149,2151,2153,2155],{"class":79,"line":232},[77,2142,1951],{"class":98},[77,2144,162],{"class":91},[77,2146,1956],{"class":165},[77,2148,162],{"class":91},[77,2150,1961],{"class":196},[77,2152,138],{"class":91},[77,2154,1966],{"class":475},[77,2156,208],{"class":91},[77,2158,2159],{"class":79,"line":237},[77,2160,125],{"emptyLinePlaceholder":124},[77,2162,2163,2165,2167,2169,2171,2173],{"class":79,"line":255},[77,2164,240],{"class":134},[77,2166,138],{"class":91},[77,2168,1951],{"class":196},[77,2170,162],{"class":91},[77,2172,1956],{"class":165},[77,2174,208],{"class":91},[77,2176,2177,2179,2181,2183,2185,2187],{"class":79,"line":271},[77,2178,240],{"class":134},[77,2180,138],{"class":91},[77,2182,1995],{"class":196},[77,2184,162],{"class":91},[77,2186,1956],{"class":165},[77,2188,208],{"class":91},[14,2190,2191],{},[18,2192,303],{},[67,2194,2196],{"className":69,"code":2195,"language":71,"meta":72,"style":72},"[95]\n[]\n",[74,2197,2198,2206],{"__ignoreMap":72},[77,2199,2200,2202,2204],{"class":79,"line":80},[77,2201,2015],{"class":91},[77,2203,1966],{"class":475},[77,2205,2020],{"class":91},[77,2207,2208],{"class":79,"line":95},[77,2209,2210],{"class":91},"[]\n",[14,2212,2213,2214,162],{},"If this topic feels confusing, it helps to understand ",[245,2215,2217],{"href":2216},"\u002Flearn\u002Fmutability-in-python-explained-mutable-vs-immutable-types\u002F","mutability in Python: mutable vs immutable types",[62,2219,2221],{"id":2220},"common-beginner-mistake-changing-through-the-object","Common beginner mistake: changing through the object",[14,2223,2224],{},"Reading a class variable through an object is fine:",[67,2226,2228],{"className":69,"code":2227,"language":71,"meta":72,"style":72},"class Car:\n    wheels = 4\n\n\ncar = Car()\nprint(car.wheels)\n",[74,2229,2230,2239,2249,2253,2257,2268],{"__ignoreMap":72},[77,2231,2232,2234,2237],{"class":79,"line":80},[77,2233,84],{"class":83},[77,2235,2236],{"class":87}," Car",[77,2238,92],{"class":91},[77,2240,2241,2244,2246],{"class":79,"line":95},[77,2242,2243],{"class":98},"    wheels ",[77,2245,103],{"class":102},[77,2247,2248],{"class":475}," 4\n",[77,2250,2251],{"class":79,"line":121},[77,2252,125],{"emptyLinePlaceholder":124},[77,2254,2255],{"class":79,"line":128},[77,2256,125],{"emptyLinePlaceholder":124},[77,2258,2259,2262,2264,2266],{"class":79,"line":155},[77,2260,2261],{"class":98},"car ",[77,2263,103],{"class":102},[77,2265,2236],{"class":196},[77,2267,1233],{"class":91},[77,2269,2270,2272,2274,2277,2279,2282],{"class":79,"line":178},[77,2271,240],{"class":134},[77,2273,138],{"class":91},[77,2275,2276],{"class":196},"car",[77,2278,162],{"class":91},[77,2280,2281],{"class":165},"wheels",[77,2283,208],{"class":91},[14,2285,2286],{},"But assigning through the object can create a new instance variable:",[67,2288,2290],{"className":69,"code":2289,"language":71,"meta":72,"style":72},"class Car:\n    wheels = 4\n\n\ncar1 = Car()\ncar2 = Car()\n\ncar1.wheels = 6\n\nprint(car1.wheels)\nprint(car2.wheels)\nprint(Car.wheels)\n",[74,2291,2292,2300,2308,2312,2316,2327,2338,2342,2356,2360,2374,2389],{"__ignoreMap":72},[77,2293,2294,2296,2298],{"class":79,"line":80},[77,2295,84],{"class":83},[77,2297,2236],{"class":87},[77,2299,92],{"class":91},[77,2301,2302,2304,2306],{"class":79,"line":95},[77,2303,2243],{"class":98},[77,2305,103],{"class":102},[77,2307,2248],{"class":475},[77,2309,2310],{"class":79,"line":121},[77,2311,125],{"emptyLinePlaceholder":124},[77,2313,2314],{"class":79,"line":128},[77,2315,125],{"emptyLinePlaceholder":124},[77,2317,2318,2321,2323,2325],{"class":79,"line":155},[77,2319,2320],{"class":98},"car1 ",[77,2322,103],{"class":102},[77,2324,2236],{"class":196},[77,2326,1233],{"class":91},[77,2328,2329,2332,2334,2336],{"class":79,"line":178},[77,2330,2331],{"class":98},"car2 ",[77,2333,103],{"class":102},[77,2335,2236],{"class":196},[77,2337,1233],{"class":91},[77,2339,2340],{"class":79,"line":183},[77,2341,125],{"emptyLinePlaceholder":124},[77,2343,2344,2347,2349,2351,2353],{"class":79,"line":188},[77,2345,2346],{"class":98},"car1",[77,2348,162],{"class":91},[77,2350,2281],{"class":165},[77,2352,169],{"class":102},[77,2354,2355],{"class":475}," 6\n",[77,2357,2358],{"class":79,"line":211},[77,2359,125],{"emptyLinePlaceholder":124},[77,2361,2362,2364,2366,2368,2370,2372],{"class":79,"line":232},[77,2363,240],{"class":134},[77,2365,138],{"class":91},[77,2367,2346],{"class":196},[77,2369,162],{"class":91},[77,2371,2281],{"class":165},[77,2373,208],{"class":91},[77,2375,2376,2378,2380,2383,2385,2387],{"class":79,"line":237},[77,2377,240],{"class":134},[77,2379,138],{"class":91},[77,2381,2382],{"class":196},"car2",[77,2384,162],{"class":91},[77,2386,2281],{"class":165},[77,2388,208],{"class":91},[77,2390,2391,2393,2395,2398,2400,2402],{"class":79,"line":255},[77,2392,240],{"class":134},[77,2394,138],{"class":91},[77,2396,2397],{"class":196},"Car",[77,2399,162],{"class":91},[77,2401,2281],{"class":165},[77,2403,208],{"class":91},[14,2405,2406],{},[18,2407,303],{},[67,2409,2411],{"className":69,"code":2410,"language":71,"meta":72,"style":72},"6\n4\n4\n",[74,2412,2413,2418,2423],{"__ignoreMap":72},[77,2414,2415],{"class":79,"line":80},[77,2416,2417],{"class":475},"6\n",[77,2419,2420],{"class":79,"line":95},[77,2421,2422],{"class":475},"4\n",[77,2424,2425],{"class":79,"line":121},[77,2426,2422],{"class":475},[14,2428,2429],{},"Important:",[27,2431,2432,2438,2443],{},[30,2433,2434,2437],{},[74,2435,2436],{},"car1.wheels = 6"," did not change the class variable",[30,2439,2440,2441],{},"it created an instance variable only on ",[74,2442,2346],{},[30,2444,2445,2447],{},[74,2446,2382],{}," still reads the value from the class",[14,2449,2450],{},"If you want to change the shared value, change it on the class:",[67,2452,2454],{"className":69,"code":2453,"language":71,"meta":72,"style":72},"class Car:\n    wheels = 4\n\n\ncar1 = Car()\ncar2 = Car()\n\nCar.wheels = 6\n\nprint(car1.wheels)\nprint(car2.wheels)\nprint(Car.wheels)\n",[74,2455,2456,2464,2472,2476,2480,2490,2500,2504,2516,2520,2534,2548],{"__ignoreMap":72},[77,2457,2458,2460,2462],{"class":79,"line":80},[77,2459,84],{"class":83},[77,2461,2236],{"class":87},[77,2463,92],{"class":91},[77,2465,2466,2468,2470],{"class":79,"line":95},[77,2467,2243],{"class":98},[77,2469,103],{"class":102},[77,2471,2248],{"class":475},[77,2473,2474],{"class":79,"line":121},[77,2475,125],{"emptyLinePlaceholder":124},[77,2477,2478],{"class":79,"line":128},[77,2479,125],{"emptyLinePlaceholder":124},[77,2481,2482,2484,2486,2488],{"class":79,"line":155},[77,2483,2320],{"class":98},[77,2485,103],{"class":102},[77,2487,2236],{"class":196},[77,2489,1233],{"class":91},[77,2491,2492,2494,2496,2498],{"class":79,"line":178},[77,2493,2331],{"class":98},[77,2495,103],{"class":102},[77,2497,2236],{"class":196},[77,2499,1233],{"class":91},[77,2501,2502],{"class":79,"line":183},[77,2503,125],{"emptyLinePlaceholder":124},[77,2505,2506,2508,2510,2512,2514],{"class":79,"line":188},[77,2507,2397],{"class":98},[77,2509,162],{"class":91},[77,2511,2281],{"class":165},[77,2513,169],{"class":102},[77,2515,2355],{"class":475},[77,2517,2518],{"class":79,"line":211},[77,2519,125],{"emptyLinePlaceholder":124},[77,2521,2522,2524,2526,2528,2530,2532],{"class":79,"line":232},[77,2523,240],{"class":134},[77,2525,138],{"class":91},[77,2527,2346],{"class":196},[77,2529,162],{"class":91},[77,2531,2281],{"class":165},[77,2533,208],{"class":91},[77,2535,2536,2538,2540,2542,2544,2546],{"class":79,"line":237},[77,2537,240],{"class":134},[77,2539,138],{"class":91},[77,2541,2382],{"class":196},[77,2543,162],{"class":91},[77,2545,2281],{"class":165},[77,2547,208],{"class":91},[77,2549,2550,2552,2554,2556,2558,2560],{"class":79,"line":255},[77,2551,240],{"class":134},[77,2553,138],{"class":91},[77,2555,2397],{"class":196},[77,2557,162],{"class":91},[77,2559,2281],{"class":165},[77,2561,208],{"class":91},[14,2563,2564],{},[18,2565,303],{},[67,2567,2569],{"className":69,"code":2568,"language":71,"meta":72,"style":72},"6\n6\n6\n",[74,2570,2571,2575,2579],{"__ignoreMap":72},[77,2572,2573],{"class":79,"line":80},[77,2574,2417],{"class":475},[77,2576,2577],{"class":79,"line":95},[77,2578,2417],{"class":475},[77,2580,2581],{"class":79,"line":121},[77,2582,2417],{"class":475},[62,2584,2586],{"id":2585},"simple-rule-to-remember","Simple rule to remember",[27,2588,2589,2595],{},[30,2590,2591,2594],{},[18,2592,2593],{},"Shared by all objects"," = class variable",[30,2596,2597,2600],{},[18,2598,2599],{},"Unique to each object"," = instance variable",[62,2602,2604],{"id":2603},"common-causes-of-confusion","Common causes of confusion",[14,2606,2607],{},"These are the most common reasons beginners mix them up:",[27,2609,2610,2613,2619,2629],{},[30,2611,2612],{},"Using a class variable for data that should be unique per object",[30,2614,2615,2616,2618],{},"Creating ",[74,2617,369],{}," and thinking it changes the class variable",[30,2620,2621,2622,873,2625,2628],{},"Using a mutable class variable like ",[74,2623,2624],{},"[]",[74,2626,2627],{},"{}"," by mistake",[30,2630,2631],{},"Not understanding that objects can read values from the class",[62,2633,2635],{"id":2634},"useful-debugging-checks","Useful debugging checks",[14,2637,2638],{},"If you are not sure where a variable is stored, these checks can help:",[67,2640,2642],{"className":69,"code":2641,"language":71,"meta":72,"style":72},"print(obj.__dict__)\nprint(ClassName.__dict__)\nprint(obj.variable_name)\nprint(ClassName.variable_name)\nprint(hasattr(obj, 'variable_name'))\n",[74,2643,2644,2659,2674,2689,2703],{"__ignoreMap":72},[77,2645,2646,2648,2650,2652,2654,2657],{"class":79,"line":80},[77,2647,240],{"class":134},[77,2649,138],{"class":91},[77,2651,1246],{"class":196},[77,2653,162],{"class":91},[77,2655,2656],{"class":158},"__dict__",[77,2658,208],{"class":91},[77,2660,2661,2663,2665,2668,2670,2672],{"class":79,"line":95},[77,2662,240],{"class":134},[77,2664,138],{"class":91},[77,2666,2667],{"class":196},"ClassName",[77,2669,162],{"class":91},[77,2671,2656],{"class":158},[77,2673,208],{"class":91},[77,2675,2676,2678,2680,2682,2684,2687],{"class":79,"line":121},[77,2677,240],{"class":134},[77,2679,138],{"class":91},[77,2681,1246],{"class":196},[77,2683,162],{"class":91},[77,2685,2686],{"class":165},"variable_name",[77,2688,208],{"class":91},[77,2690,2691,2693,2695,2697,2699,2701],{"class":79,"line":128},[77,2692,240],{"class":134},[77,2694,138],{"class":91},[77,2696,2667],{"class":196},[77,2698,162],{"class":91},[77,2700,2686],{"class":165},[77,2702,208],{"class":91},[77,2704,2705,2707,2709,2712,2714,2716,2718,2721,2723,2726],{"class":79,"line":155},[77,2706,240],{"class":134},[77,2708,138],{"class":91},[77,2710,2711],{"class":134},"hasattr",[77,2713,138],{"class":91},[77,2715,1246],{"class":196},[77,2717,145],{"class":91},[77,2719,2720],{"class":106}," '",[77,2722,2686],{"class":110},[77,2724,2725],{"class":106},"'",[77,2727,2728],{"class":91},"))\n",[14,2730,2731],{},"What they do:",[27,2733,2734,2740,2746,2751,2757],{},[30,2735,2736,2739],{},[74,2737,2738],{},"obj.__dict__"," shows the instance variables on that object",[30,2741,2742,2745],{},[74,2743,2744],{},"ClassName.__dict__"," shows attributes on the class",[30,2747,2748,2750],{},[74,2749,1169],{}," shows what Python finds when looking through the object",[30,2752,2753,2756],{},[74,2754,2755],{},"ClassName.variable_name"," reads directly from the class",[30,2758,2759,2762],{},[74,2760,2761],{},"hasattr(obj, 'variable_name')"," checks whether the object can access that name",[14,2764,384],{},[67,2766,2768],{"className":69,"code":2767,"language":71,"meta":72,"style":72},"class Dog:\n    species = \"Canis familiaris\"\n\n    def __init__(self, name):\n        self.name = name\n\n\ndog = Dog(\"Max\")\n\nprint(dog.__dict__)\nprint(Dog.__dict__['species'])\n",[74,2769,2770,2778,2790,2794,2810,2822,2826,2830,2849,2853,2868],{"__ignoreMap":72},[77,2771,2772,2774,2776],{"class":79,"line":80},[77,2773,84],{"class":83},[77,2775,88],{"class":87},[77,2777,92],{"class":91},[77,2779,2780,2782,2784,2786,2788],{"class":79,"line":95},[77,2781,99],{"class":98},[77,2783,103],{"class":102},[77,2785,107],{"class":106},[77,2787,111],{"class":110},[77,2789,599],{"class":106},[77,2791,2792],{"class":79,"line":121},[77,2793,125],{"emptyLinePlaceholder":124},[77,2795,2796,2798,2800,2802,2804,2806,2808],{"class":79,"line":128},[77,2797,131],{"class":83},[77,2799,135],{"class":134},[77,2801,138],{"class":91},[77,2803,142],{"class":141},[77,2805,145],{"class":91},[77,2807,149],{"class":148},[77,2809,152],{"class":91},[77,2811,2812,2814,2816,2818,2820],{"class":79,"line":155},[77,2813,159],{"class":158},[77,2815,162],{"class":91},[77,2817,166],{"class":165},[77,2819,169],{"class":102},[77,2821,431],{"class":98},[77,2823,2824],{"class":79,"line":178},[77,2825,125],{"emptyLinePlaceholder":124},[77,2827,2828],{"class":79,"line":183},[77,2829,125],{"emptyLinePlaceholder":124},[77,2831,2832,2835,2837,2839,2841,2843,2845,2847],{"class":79,"line":188},[77,2833,2834],{"class":98},"dog ",[77,2836,103],{"class":102},[77,2838,88],{"class":196},[77,2840,138],{"class":91},[77,2842,114],{"class":106},[77,2844,203],{"class":110},[77,2846,114],{"class":106},[77,2848,208],{"class":91},[77,2850,2851],{"class":79,"line":211},[77,2852,125],{"emptyLinePlaceholder":124},[77,2854,2855,2857,2859,2862,2864,2866],{"class":79,"line":232},[77,2856,240],{"class":134},[77,2858,138],{"class":91},[77,2860,2861],{"class":196},"dog",[77,2863,162],{"class":91},[77,2865,2656],{"class":158},[77,2867,208],{"class":91},[77,2869,2870,2872,2874,2876,2878,2880,2882,2884,2886,2888],{"class":79,"line":237},[77,2871,240],{"class":134},[77,2873,138],{"class":91},[77,2875,778],{"class":196},[77,2877,162],{"class":91},[77,2879,2656],{"class":158},[77,2881,2015],{"class":91},[77,2883,2725],{"class":106},[77,2885,250],{"class":110},[77,2887,2725],{"class":106},[77,2889,2890],{"class":91},"])\n",[14,2892,2893],{},[18,2894,303],{},[67,2896,2898],{"className":69,"code":2897,"language":71,"meta":72,"style":72},"{'name': 'Max'}\nCanis familiaris\n",[74,2899,2900,2923],{"__ignoreMap":72},[77,2901,2902,2905,2907,2909,2911,2914,2916,2918,2920],{"class":79,"line":80},[77,2903,2904],{"class":91},"{",[77,2906,2725],{"class":106},[77,2908,166],{"class":110},[77,2910,2725],{"class":106},[77,2912,2913],{"class":91},":",[77,2915,2720],{"class":106},[77,2917,203],{"class":110},[77,2919,2725],{"class":106},[77,2921,2922],{"class":91},"}\n",[77,2924,2925],{"class":79,"line":95},[77,2926,313],{"class":98},[14,2928,2929],{},"This shows:",[27,2931,2932,2937],{},[30,2933,2934,2936],{},[74,2935,166],{}," is stored on the object",[30,2938,2939,2941],{},[74,2940,250],{}," is stored on the class",[62,2943,2945],{"id":2944},"faq","FAQ",[2947,2948,2950],"h3",{"id":2949},"can-an-object-access-a-class-variable","Can an object access a class variable?",[14,2952,2953],{},"Yes. If the object does not have an instance variable with that name, Python reads the value from the class.",[2947,2955,2957],{"id":2956},"can-a-class-variable-be-changed","Can a class variable be changed?",[14,2959,2960],{},"Yes. Change it on the class when you want the shared value to update for all objects.",[2947,2962,2964],{"id":2963},"why-did-changing-a-class-variable-on-one-object-only-affect-that-object","Why did changing a class variable on one object only affect that object?",[14,2966,2967],{},"You likely created a new instance variable with the same name instead of changing the variable on the class.",[2947,2969,2971],{"id":2970},"should-i-put-lists-and-dictionaries-in-class-variables","Should I put lists and dictionaries in class variables?",[14,2973,2974],{},"Only if you want all objects to share the same list or dictionary. Otherwise use an instance variable.",[62,2976,2978],{"id":2977},"see-also","See also",[27,2980,2981,2985,2992,2998,3003,3008],{},[30,2982,2983],{},[245,2984,872],{"href":871},[30,2986,2987],{},[245,2988,2989,2990,381],{"href":377},"The ",[74,2991,373],{},[30,2993,2994],{},[245,2995,2997],{"href":2996},"\u002Flearn\u002Fbasic-methods-in-python-classes-explained\u002F","Basic methods in Python classes explained",[30,2999,3000],{},[245,3001,3002],{"href":2216},"Mutability in Python explained: mutable vs immutable types",[30,3004,3005],{},[245,3006,3007],{"href":876},"What is a class in Python",[30,3009,3010],{},[245,3011,3012],{"href":1413},"What is an object in Python",[3014,3015,3016],"style",{},"html pre.shiki code .sbsja, html code.shiki .sbsja{--shiki-light:#9C3EDA;--shiki-default:#D73A49;--shiki-dark:#F97583}html pre.shiki code .sbgvK, html code.shiki .sbgvK{--shiki-light:#E2931D;--shiki-default:#6F42C1;--shiki-dark:#B392F0}html pre.shiki code .sP7_E, html code.shiki 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