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 Unindent main()以及它下面的内容，现在它是Temp不是独立函数的方法。 您实际上是在尝试调用没有Temp实例的方法。 
 
 缩进是python如何确定方法，类，循环中的内容。 看这里： 
 
 编辑 ： 
 
class Temp():
    def __init__(self):
        # this method is in Temp
        pass

    def prettyPrint(self):
        # this method is also in temp
        print("I'm in temp")

def prettyPrint(self):
    #this is not in Temp (notice the indentation change)
    print("I'm not in temp")

if __name__ == "__main__":
    #this is not in temp either
    t = Temp()
    t.prettyPrint()
    prettyPrint(None)

Unindent main() and what's below it, right now it's a method of Temp not standalone function. You're essentially trying to call a method without an instance of Temp.
 
Indentation is how python determines what is in a method, class, loop or not. See here:
 
EDIT:
 
class Temp():
    def __init__(self):
        # this method is in Temp
        pass

    def prettyPrint(self):
        # this method is also in temp
        print("I'm in temp")

def prettyPrint(self):
    #this is not in Temp (notice the indentation change)
    print("I'm not in temp")

if __name__ == "__main__":
    #this is not in temp either
    t = Temp()
    t.prettyPrint()
    prettyPrint(None)