It's most likely that you've done something like the following:

def myfunc():
    i=73
    return i
out = myfunc()
print 'the number is: ' + i

The mistake seen here is a common one, and easy to make. In a language such as Python, where variables are not declared before use, and exist as untyped until given data, programmers often forget that as in other languages, variables loaded with specific types of data do have an allowable set of operations for the type.
In the code above, an attempt is made to concatenate two objects in a print statement. However, string concatenation is not allowable with integer types, which is what the return value of myfunc() was implicitly declared as when 73 was assigned to i in the function.
A better way to do this would be as follows...

import string
def myfunc():
   i=73
   return i
out = myfunc()
print 'the number is' + str(i)

I just wanted to add this FQA because a coworker had this problem today, and it seems like a problem that a lot of people who are programming in Python tend to make, then bang their heads against the wall because they forget that some operations are restricted to specific types.