TypeError: unbound method a() must be called with A instance as first argument (got nothing instead)

>>> class A:
def a(self):
print("I'm a")

>>> A.a()

Traceback (most recent call last):
File "<pyshell#10>", line 1, in <module>
A.a()
TypeError: unbound method a() must be called with A instance as first argument (got nothing instead)

错误原因：函数a()非静态方法，故需实例化然后才能使用，改正如下：
class A:
def a(self):
print("I'm a")

obj = A()
obj.a()

或者将a()改为静态方法即可，如下：
[code]class A:
@staticmethod
def a():
print ("I'm a")

A.a()