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 1