need help regarding creating a .py file and executing it using the shell(GUI).

[suhas bose]

hi, I've read through a couple threads related to my question but i guess i haven't been able to find the right one. so here's my question again..
need the right format to create a .py file( actually i did create a .py file! :P but the thing is i'm not sure if it's executable). My file has a function defined in it and that is all. am i supposed to add extra commands into it before saving the file? because when i type .py file name in the shell it gives something like this..
>>> spelling.py

Traceback (most recent call last):
File "<pyshell#4>", line 1, in <module>
spelling.py
NameError: name 'spelling' is not defined

i'm doing this on python2.7.1(IDLE) in windows. it's the same even with the command line..
also, i want to know how i can input the argument after executing the file.

the contents of the file:(it's for a spell check)

def spell(arg):
    b=arg
    a=arg
    s=[]
    for i in range(len(b)):
        i=arg[i]
        arg=arg.replace(i,'')
        s.append(arg)
        arg=a
    alph=list('abcdefghijklmnopqrstuvwxyz')
    for i in range(len(arg)):
        i=arg[i]
        for j in range(26):
            j=alph[j]
            arg=arg.replace(i,j)
            s.append(arg)
            arg=a
    for i in range(len(arg)):
        for j in range(26):
            arg=arg[:i]+alph[j]+arg[i:]
            s.append(arg)
            arg=a
        for j in range(26):
            arg=arg+alph[j]
            s.append(arg)
            arg=a    
    y=open('text.txt')
    x=y.read()
    x=x.split()
    for i in s:
        z=x.count(i)
        if z!=0:
            print i
    y.close()

[Bishop Manu]

try to import spelling.py,
then you can call the function from the shell! :)

[suhas bose]

thanks, but i couldn't call it that way. had to put in the lines
if__name__=="__main__":
spell(raw_input(""))

at the end.found this in someone's program :P. now it works just the way i wanted.
this thread is answered.