python - argv function not working

Let me comment your code:

script, x, y, z = argv
# we now have four new variables inside the main module: 
# script, x, y, z
# all functions defined here have access to these but
# cannot modify them (unless we use "global").

def sum(x, y, z):
    # while sum() in principle has access to the 
    # variables defined outside of sum(),
    # sum() (the function) also takes three parameters.
    # these need to be passed in with a function call
    # (i.e. sum(x, y, z)).
    #
    # x, y, z here are unrelated to x, y, z outside of sum().
    # in fact the parameters shadow the global variables,
    # making them inaccessible (via direct means).
    if x == y or y == z or x==z:  
        sum = 0  
        # this defines a local variable "sum".
        # it is unrelated to the function "sum"
    else:  
        sum = x + y + z  
        # x, y, z are strings, so "sum" is now a string, too.
    return sum

print (sum)
# here, you refer to the function "sum".
# the variable "sum" only exists inside the function "sum".

If you want the result of sum() (the function), you need call it with parameters:

print(sum(x, y, z))

You cannot access the variable sum outside of the function.

If you

print(sum)

then you print the function sum.

If you want to print the result, you must call sum:

print(sum(x, y, z))

print (sum(x,y,z))

means call your function/method and print the return value.

print (sum) 

means print the meta data of your data(sum is also a type of data)

You should print the result of the sum function :

print(sum(x, y, z))

This way the return value of the sum function will be printed out. The way you did it, just prints out a function reference.

Also as a side note, that sum() is a built-in python function, so it's best to avoid naming conflicts and name your functions accordingly.

Try the following code:

from sys import argv
script, x, y, z = argv

def sum_(x, y, z):  
    if x == y or y == z or x==z:  
        the_sum = 0  
    else:  
        the_sum = int(x) + int(y) + int(z)  
    return the_sum  
print(sum_(x, y, z))