problem using differ

[Russell]

I'm trying to automate the comparison of some source code but I'm having
trouble using the differ object.  I'm new to Python so I'm probably doing
something wrong.  I've created a small program (included below) that
demonstrates my problem.  For some reason, Python doesn't recognize differ.
I keep getting this error: NameError: name 'differ' is not defined.  What am
I doing wrong?

Test Code follows:
import difflib

a=[]
a.append('1. Beautiful is better than ugly.')
a.append('2. Explicit is better than implicit.')
a.append('3. Simple is better than complex.')
a.append('4. Complex is better than complicated.')

b=[]
b.append('1. Beautiful is better than ugly.')
b.append('3.   Simple is better than complex.')
b.append('4. Complicated is better than complex.')
b.append('5. Flat is better than nested.')

d=differ()
d.compare(a,b)