NameError: name 'self' is not defined

python nameerror
chriss picture chriss · Nov 26, 2009 · Viewed 159.5k times · Source

Why such structure

class A:
    def __init__(self, a):
        self.a = a

    def p(self, b=self.a):
        print b

gives an error NameError: name 'self' is not defined?

Answer

intgr picture intgr · Nov 26, 2009

Default argument values are evaluated at function define-time, but self is an argument only available at function call time. Thus arguments in the argument list cannot refer each other.

It's a common pattern to default an argument to None and add a test for that in code:

def p(self, b=None):
    if b is None:
        b = self.a
    print b

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