Python splitting code into functions

Question

Sorry about the length of this but I figured more info is better than not enough!!

I'm trying to split the (working) piece of Python code into functions to make it clearer / easier to use but am coming unstuck as soon as i move stuff into functions. It's basically a password generator which tries to only output a password to the user once the password qualifies as having a character from all 4 categories in it. (Lowercase, uppercase, numbers and symbols).

---

import random
import string
lowerasciis = string.ascii_letters[0:26]
upperasciis = string.ascii_letters[26:]
numberedstrings = str(1234567809)
symbols = "!@$%^&*()[]"
password_length = int(raw_input("Please enter a password length: "))

while True:
    lowerasscii_score = 0
    upperascii_score = 0
    numberedstring_score = 0
    symbol_score = 0
    password_as_list = []

    while len(password_as_list) < password_length:
        char = random.choice(lowerasciis+upperasciis+numberedstrings+symbols)
        password_as_list.append(char)
    for x in password_as_list:
        if x in lowerasciis:
            lowerasscii_score +=1
        elif x in upperasciis:
            upperascii_score +=1
        elif x in numberedstrings:
            numberedstring_score +=1
        elif x in symbols:
            symbol_score +=1
# a check for the screen. Each cycle of the loop should display a new score:
    print lowerasscii_score, upperascii_score, numberedstring_score, symbol_score 

    if lowerasscii_score >= 1 and upperascii_score >= 1 and numberedstring_score >= 1 and symbol_score >=1:
        password = "".join(password_as_list)
        print password
        break

And here is my attempt at splitting it. When i try to run the below it complains of "UnboundLocalError: local variable 'upperascii_score' referenced before assignment" in the scorepassword_as_a_list() function

import random
import string
lowerasciis = string.ascii_letters[0:26]
upperasciis = string.ascii_letters[26:]
numberedstrings = str(1234567809)
symbols = "!@$%^&*()[]"
password_length = int(raw_input("Please enter a password length: "))
lowerasscii_score = 0
upperascii_score = 0
numberedstring_score = 0
symbol_score = 0
password_as_list = []

def genpassword_as_a_list():
    while len(password_as_list) < password_length:
        char = random.choice(lowerasciis+upperasciis+numberedstrings+symbols)
        password_as_list.append(char)

def scorepassword_as_a_list():
    for x in password_as_list:
        if x in lowerasciis:
            lowerasscii_score +=1
        elif x in upperasciis:
            upperascii_score +=1
        elif x in numberedstrings:
            numberedstring_score +=1
        elif x in symbols:
            symbol_score +=1
    # give user feedback about password's score in 4 categories
    print lowerasscii_score, upperascii_score, numberedstring_score, symbol_score

def checkscore():
    if lowerasscii_score >= 1 and upperascii_score >= 1 and numberedstring_score >= 1 and symbol_score >=1:
        return 1
    else:
        return 0

def join_and_printpassword():
    password = "".join(password_as_list)
    print password  

while True:
    genpassword_as_a_list()
    scorepassword_as_a_list()
    if checkscore() == 1:
        join_and_printpassword()
        break

Answer 1

The primary issue here is that you need to keep track of the scope of the various variables that you're using. In general, one of the advantages of splitting your code into functions (if done properly) is that you can reuse code without worrying about whether any initial states have been modified somewhere else. To be concrete, in your particular example, even if you got things working right (using global variables), every time you called one of your functions, you'd have to worry that e.g. lowerassci_score was not getting reset to 0.

Instead, you should accept anything that your function needs to run as parameters and output some return value, without manipulating global variables. In general, this idea is known as "avoiding side-effects." Here is your example re-written with this in mind:

import random
import string
lowerasciis = string.ascii_letters[0:26]
upperasciis = string.ascii_letters[26:]
numberedstrings = str(1234567809)
symbols = "!@$%^&*()[]"

def genpassword_as_a_list(password_length):
    password_as_list = []
    while len(password_as_list) < password_length:
        char = random.choice(lowerasciis+upperasciis+numberedstrings+symbols)
        password_as_list.append(char)
    return password_as_list

def scorepassword_as_a_list(password_as_list):
    lowerasscii_score = 0
    upperascii_score = 0
    numberedstring_score = 0
    symbol_score = 0
    for x in password_as_list:
        if x in lowerasciis:
            lowerasscii_score +=1
        elif x in upperasciis:
            upperascii_score +=1
        elif x in numberedstrings:
            numberedstring_score +=1
        elif x in symbols:
            symbol_score +=1
    # give user feedback about password's score in 4 categories
    return (
        lowerasscii_score, upperascii_score, numberedstring_score,
        symbol_score
    )

def checkscore(
        lowerasscii_score, upperascii_score, numberedstring_score,
        symbol_score):
    if lowerasscii_score >= 1 and upperascii_score >= 1 and numberedstring_score >= 1 and symbol_score >=1:
        return 1
    else:
        return 0

def join_and_printpassword(password_as_list):
    password = "".join(password_as_list)
    print password  

password_length = int(raw_input("Please enter a password length: "))

while True:
    password_list = genpassword_as_a_list(password_length)
    current_score = scorepassword_as_a_list(password_list)
    if checkscore(*current_score) == 1:
        join_and_printpassword(password_list)
        break

A few notes on this:

1. Notice that the "score" variables are introduced inside the scorepassword_as_list function and (based on the scoping rules) are local to that function. We get them out of the function by passing them out as a return value.
2. I've used just a bit of magic near the end with *current_score. Here, the asterisk is used as the "splat" or "unpack" operator. I could just as easily have written checkscore(current_score[0], current_score[1], current_score[2], current_score[3]); they mean the same thing.

It would probably be useful to read up a bit more on variable scoping and namespaces in Python. Here's one guide, but there may be better ones out there.