python class variable not visible in __init__?

Question

This code produces an error message, which I found surprising:

class Foo(object):
    custom = 1
    def __init__(self, custom=Foo.custom):
        self._custom          


        

Answer 1

I get the following error:

Traceback (most recent call last):
  Line 1, in 
    class Foo(object):
  Line 3, in Foo
    def __init__(self, custom=Foo.custom):
NameError: name 'Foo' is not defined

This is because the name Foo is in the process of being defined as the __init__ function is defined, and is not fully available at that time.

The solution is to avoid using the name Foo in the function definition (I also renamed the custom paramter to acustom to distinguish it from Foo.custom):

class Foo(object):
    custom = 1
    def __init__(self, acustom=custom):
        self._custom = acustom
x = Foo()
print x._custom