IndentationError: unindent does not match any outer indentation level

One possible cause for this error is that there might be spaces mixed with tabs for indentation. Try doing a search & replace to replace all tabs with a few spaces.

Try this:

import sys

def Factorial(n): # return factorial
    result = 1
    for i in range (1,n):
        result = result * i
    print "factorial is ",result
    return result

print Factorial(10)

To easily check for problems with tabs/spaces you can actually do this:

python -m tabnanny yourfile.py

or you can just set up your editor correctly of course :-)

Are you sure you are not mixing tabs and spaces in your indentation white space? (That will cause that error.)

Note, it is recommended that you don't use tabs in Python code. See the style guide. You should configure Notepad++ to insert spaces for tabs.

Whenever I've encountered this error, it's because I've somehow mixed up tabs and spaces in my editor.