[Tutor] need help with conditionals

[wrobl1rt at cmich.edu]

Hello all, 
I am still very new to Python and am working on conditionals. Im stuck on this 
problem and I'm sorry if this is something really simple that I'm missing but its 
been really frustrating me. Here's a copy of the problem, and sorry if its really 
long but its the end question about the logically equivalent expressions I'm 
stuck on. Anyways, heres a copy of the problem

-----------------------------------------------------------

To better understand boolean expressions, it is helpful to construct truth tables. 
Two boolean expressions are logically equivalent if and only if they have the 
same truth table.

The following Python script prints out the truth table for the any boolean 
expression in two variables: p and q:

expression = raw_input("Enter a boolean expression in two variables, p and q: ")

print " p      q      %s"  % expression
length = len( " p      q      %s"  % expression)
print length*"="

for p in True, False:
    for q in True, False:
        print "%-7s %-7s %-7s" % (p, q, eval(expression))
You will learn how this script works in later chapters. For now, you will use it to 
learn about boolean expressions. Copy this program to a file named 
p_and_q.py, then run it from the command line and give it: p or q, when 
prompted for a boolean expression. You should get the following output:

 p      q      p or q
=====================
True    True    True
True    False   True
False   True    True
False   False   False
Now that we see how it works, let’s wrap it in a function to make it easier to 
use:

def truth_table(expression):
    print " p      q      %s"  % expression
    length = len( " p      q      %s"  % expression)
    print length*"="

    for p in True, False:
        for q in True, False:
            print "%-7s %-7s %-7s" % (p, q, eval(expression))
We can import it into a Python shell and call truth_table with a string containing 
our boolean expression in p and q as an argument:

>>> from p_and_q import *
>>> truth_table("p or q")
p      q      p or q
=====================
True    True    True
True    False   True
False   True    True
False   False   False
>>>
Use the truth_table functions with the following boolean expressions, recording 
the truth table produced each time:

not(p or q)
p and q
not(p and q)
not(p) or not(q)
not(p) and not(q)
Which of these are logically equivalent?
-------------------------------------------------

Whenever I try to enter the expressions listed into the prompt it tells me the 
string object is not callable....