NameError: name 'self' is not defined
nameerror, python
Solution
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
Update 2022: Python developers are now considering late-bound argument defaults for future Python versions.
Problem
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`?