chriss chriss - 1 month ago 6
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
?

Answer

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