0

I am using python 2.7. I wrote a code to generate passwords. For doing this, I used the random module to generate how many characters of different types(uppercase, lowercase, special and numbers) to be used to generate a password of a given length. When a wrote a function for this, it was supposed to return a tuple, but it returns None. Why is it happening?

I tried the casual debugging method of putting print statements in between and figuring out where it went wrong. Everything works just fine, except it returns None. 

def passlen(a):
    """Gives length of different characters to be put into passwords"""
    uplen=random.randrange(0, a)
    lwlen=random.randrange(0, a)
    speclen=random.randrange(0, a)
    nmbrlen=random.randrange(0, a)
    if uplen+lwlen+speclen+nmbrlen==a:
        print (uplen, lwlen, speclen, nmbrlen)
        return(uplen, lwlen, speclen, nmbrlen)
    else:
        passlen(a)

x=input("how many characters in the password?")

print(passlen(x))

Expected results are 4-tuples, but it gives None instead.

Improve this question
7
  • where is Your return statement? o_0 Commented Apr 25, 2019 at 10:07
  • right above the else statement Commented Apr 25, 2019 at 10:09
  • So... most of the time it's not being executed, wherefore the function returns None. Commented Apr 25, 2019 at 10:10
  • But isn't a function only supposed to return at the end of a return statement? And it returns None if no return statement is found. Commented Apr 25, 2019 at 10:15
  • So, most of the time Your function does not reach the end statement. Only if the sum is equal to a. You have None when the function exits without explicit return statement. It's sounds better then just guessing what did You actually wanted to return. Commented Apr 25, 2019 at 10:19

3 Answers 3

Reset to default
1

So you want four random numbers that add to a? Of course you can try choosing four random numbers until you find a set that adds up to a, but that might take a while for large values of a (and you definitely don't want to do this recursively).

Much better to choose three split points between 0 and a:

def passlen(a):
    splits = sorted([random.randrange(0,a) for _ in range(3)])
    uplen = splits[0]
    lwlen = splits[1] - uplen
    speclen = splits[2] - uplen - lwlen
    nmbrlen = a - uplen - lwlen - speclen
    return uplen, lwlen, speclen, nmbrlen
Improve this answer
Sign up to request clarification or add additional context in comments.

Comments

0

Thanks to Kamiccolo for trying to help out.

The function should look like this:

def passlen(a):
    """Gives length of different characters to be put into passwords"""
    uplen=int(random.randrange(0, a))
    lwlen=int(random.randrange(0, a))
    speclen=int(random.randrange(0, a))
    nmbrlen=int(random.randrange(0, a))
    bab=(uplen, lwlen, speclen, nmbrlen)
    if uplen+lwlen+speclen+nmbrlen==a:
        return bab
    else:
        return passlen(a)

A duplicate thread also helped me in this.

Improve this answer

2 Comments

This is problematic. You can expect a StackOverflowError with this code for large enough values of a because instead of simply looping until you get a suitable result, you keep calling the same function recursively. And you don't actually need a loop at all.
This is the best answer to the question of why the "function returns none instead of a tuple". The recursion depth of python is defaulted at 1,000... so fingers crossed that the random numbers give the desired results, but, this is the answer to the question asked w/o regard to code quality.
-1 
import random

def passlen(a):
    """Gives length of different characters to be put into passwords"""
    uplen = random.randrange(0, a)
    lwlen = random.randrange(0, a)
    speclen = random.randrange(0, a)
    nmbrlen = random.randrange(0, a)
    if uplen + lwlen + speclen + nmbrlen == a:
        print("Length of Uppercase:", uplen)
        print("Length of Lowercase:", lwlen)
        print("Length of Special characters:", speclen)
        print("Length of Numeric characters:", nmbrlen)
        return (uplen, lwlen, speclen, nmbrlen)
    else:
        return passlen(a)

x = int(input("How many characters in the password? "))  # Convert input to integer

print("Generated Password Lengths:", passlen(x))
Improve this answer

1 Comment

As it’s currently written, your answer is unclear. Please edit to add additional details that will help others understand how this addresses the question asked. You can find more information on how to write good answers in the help center.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Start asking to get answers

Find the answer to your question by asking.

Ask question

Explore related questions

See similar questions with these tags.