chriss chriss - 6 months ago 38
Python Question

NameError: name 'self' is not defined

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


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