Python Password Generator with custom parameters

Question

I have the following code here

It's a password generator that lets you choose a completely random password with a certain length of a custom password with different amounts of character types.

I want feedback of the general readability, style, and security (as it's a password generator), and if you would do anything differently.

The code:

# Imports libraries
import secrets
import string

# Creates list of every possible character for the "general" option
fulllist = string.ascii_lowercase + string.ascii_uppercase + string.digits + string.punctuation
# Asks user what option they want
generalorcustom = input("General (g) or custom (c) password: ")
# Randomly grabs a character from the 'fulllist' as many times as specified
def general():
    return ''.join(secrets.choice(fulllist) for i in range(int(length))) 

def custom():
    # Inputs how many of each character user wants
    lowernum = input("Lowwer case character count: ")
    uppernum = input("Upper case character count: ")
    digitnum = input("Digit count: ")
    specnum = input("Special character count: ")
    # Creates list, then randomly adds each characters of each type to list for specified amount
    temp_list = []
    temp_list.extend(list(secrets.choice(string.ascii_lowercase) for i in range(int(lowernum))))
    temp_list.extend(list(secrets.choice(string.ascii_uppercase) for i in range(int(uppernum))))
    temp_list.extend(list(secrets.choice(string.digits) for i in range(int(digitnum))))
    temp_list.extend(list(secrets.choice(string.punctuation) for i in range(int(specnum))))
    # Creates final string, and randomly adds contents of temp_list to final string
    password = ''
    rangevar = list(range(len(temp_list)))
    while len(rangevar) > 0:
        picked_item = secrets.choice(rangevar)
        password += temp_list[picked_item]
        rangevar.remove(picked_item)

    return password
# Checks and executes function as user requested
if generalorcustom.lower() == "general" or generalorcustom.lower() == "g":
    length = input("Password length: ")
    print(general())
elif generalorcustom.lower() == "custom" or generalorcustom.lower() == "c":
    print(custom())
else:
    print('Error, invalid input')

Answer 1

A few minor inconsistencies and maybe two improvements.

PEP 8 styling or your own in other places uses lower_case_with_underscores but some variables like fulllist don't and that's alot of ls. For readability update variables accordingly (also generalorcustom).

Move .lower() to input so its only called once not 4 times.

In custom you get the password options then generate a list of indices to pick from. A more optimal solution would be to just shuffle temp_list (Fisher-Yates shuffle) as you have all the characters for the password you just want to scramble them now. After the shuffle you can use ''.join(temp_list)

Full shuffle:

for i in range(len(temp_list)-1, 1, -1):
    j=secrets.randbelow(i+1)
    temp = temp_list[i]
    temp_list[i] = temp_list[j]
    temp_list[j] = temp

return ''.join(temp_list)

You don't have any handlers for if the user enters invalid input for a number (like a letter or negative). I'd make a function that takes a prompt and returns a number if valid otherwise continues to prompt for a number, like so:

def get_number_input(prompt):
    num=0
    while True:
        try:
            num = int(input(prompt))
            if num < 0:
                print('Please enter a positive number')
                continue
            break
        except ValueError:
            print('Please enter a number')
    return num

Instead of a single run, I would wrap the input with a while loop so a user could generate multiple passwords, with some sort of break/exit option added.

I would avoid the global length and instead pass length as a parameter to general

Everything together:

import secrets
import string

# Creates list of every possible character for the "general" option
full_list = string.ascii_lowercase + string.ascii_uppercase + string.digits + string.punctuation

def get_number_input(prompt):
    num = 0
    while True:
        try:
            num = int(input(prompt))
            if num < 0:
                print('Please enter a positive number')
                continue
            break
        except ValueError:
            print('Please enter a number')
    return num

# Randomly grabs a character from the 'full_list' as many times as specified
def general(length):
    return ''.join(secrets.choice(full_list) for i in range(length)) 

def custom():
    # Inputs how many of each character user wants
    lower_num = get_number_input("Lower case character count: ")
    upper_num = get_number_input("Upper case character count: ")
    digit_num = get_number_input("Digit count: ")
    spec_num = get_number_input("Special character count: ")
    # Creates list, then randomly adds each characters of each type to list for specified amount
    temp_list = []
    temp_list.extend(list(secrets.choice(string.ascii_lowercase) for i in range(lower_num)))
    temp_list.extend(list(secrets.choice(string.ascii_uppercase) for i in range(upper_num)))
    temp_list.extend(list(secrets.choice(string.digits) for i in range(digit_num)))
    temp_list.extend(list(secrets.choice(string.punctuation) for i in range(spec_num)))
    # shuffle choices
    for i in range(len(temp_list)-1,1,-1):
        j=secrets.randbelow(i+1)
        temp=temp_list[i]
        temp_list[i]=temp_list[j]
        temp_list[j]=temp
    return ''.join(temp_list)

while True:
    # Asks user what option they want
    general_or_custom = input("General (g) or custom (c) password: ").lower()
    # Checks and executes function as user requested
    if general_or_custom == "general" or general_or_custom == "g":
        length = get_number_input("Password length: ")
        print(general(length))
    elif general_or_custom == "custom" or general_or_custom == "c":
        print(custom())
    else:
        print('Error, invalid input')
        break