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')

• chepner: Regarding security, longer passwords of only lowercase letters are stronger than shorter passwords containing mix. A 13-character lowercase-only password is harder to crack than a 10-character password that could have uppercase letters, lowercase letters, or digits. (26**13 > 62**10). Forcing users to use any specific mix of characters encourages shorter passwords, because they're easier to remember or type.

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