NameError: name 'self' is not defined
For cases where you also wish to have the option of setting 'b' to None:
def p(self, **kwargs):
b = kwargs.get('b', self.a)
print b
A self
NameError
can also occur if you fail to define self inside a method signature. This error typically will appear as TypeError
, as there will be a mismatch between expected and given arguments[1]. However, if you accept a variable number of arguments, self
will be arg[0]
, and the variable self
will be undefined.
A minimal example.
class Obj:
def foo(*args):
print(self.bar)
>NameError: name 'self' is not defined
Correction:
class Obj:
def baz(self, *args):
print(self.bar)
[1] http://neopythonic.blogspot.com/2008/10/why-explicit-self-has-to-stay.html
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.