user1876508 user1876508 - 2 months ago 7
Python Question

How can I dynamically create class methods for a class in python

If I define a little python program as

class a():
def _func(self):
return "asdf"

# Not sure what to resplace __init__ with so that a.func will return asdf
def __init__(self, *args, **kwargs):
setattr(self, 'func', classmethod(self._func))

if __name__ == "__main__":
a.func


I receive the traceback error

Traceback (most recent call last):
File "setattr_static.py", line 9, in <module>
a.func
AttributeError: class a has no attribute 'func'


What I am trying to figure out is, how can I dynamically set a class method to a class without instantiating an object?




Edit:



The answer for this problem is

class a():
pass

def func(cls, some_other_argument):
return some_other_argument

setattr(a, 'func', classmethod(func))

if __name__ == "__main__":
print(a.func)
print(a.func("asdf"))


returns the following output

<bound method type.func of <class '__main__.a'>>
asdf

Answer

You can dynamically add a classmethod to a class by simple assignment to the class object or by setattr on the class object. Here I'm using the python convention that classes start with capital letters to reduce confusion:

# define a class object (your class may be more complicated than this...)
class A(object):
    pass

# a class method takes the class object as its first variable
def func(cls):
    print 'I am a class method'

# you can just add it to the class if you already know the name you want to use
A.func = classmethod(func)

# or you can auto-generate the name and set it this way
the_name = 'other_func' 
setattr(A, the_name, classmethod(func))
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