Learning Python for Forensics

NameError

NameErrors occur when referring to variables that do not exist in the current context:

>>> myvariable += 1
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
NameError: name 'myvariable' is not defined

Let's break this down, the issue at hand is that we're trying to add 1 to myvariable which hasn't been created yet. Python gets confused when you try to perform some action with an object that does not exist at that point in time.

A solution for this error would be to create the variable before performing said operation or using a try and except block as follows:

>>> myvariable = 0
>>> myvariable += 1
>>> print myvariable
1
>>> try:
...     myvariable += 1
... except NameError:
...     myvariable = 1
...
>>> print m
yvariable ...