對于classmethods,第一個參數是調用類方法的類,而不是通常的self for instance方法(除非另有說明,否則隱式地使用類中的所有方法).

這是一個例子 – 為了練習,我添加了一個檢查cls參數標識的異常.

class Base(object):

@classmethod

def acquire(cls, param):

if cls is Base:

raise Exception("Must be called via subclass :(")

return "this is the result of `acquire`ing a %r with %r" % (cls, param)

class Something(Base):

pass

class AnotherThing(Base):

pass

print Something.acquire("example")

print AnotherThing.acquire("another example")

print Base.acquire("this will crash")

this is the result of `acquire`ing a with 'example'

this is the result of `acquire`ing a with 'another example'

Traceback (most recent call last):

File "classmethod.py", line 16, in

print Base.acquire("this will crash")

File "classmethod.py", line 5, in acquire

raise Exception("Must be called via subclass :(")

Exception: Must be called via subclass :(

總結

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