如何检查输入是否包含 Python 中的特殊字符？

Question

I am a high school programmer currently writing code in Python to strengthen my programming skills and am creating a basic signup page. I want my code to alert the user if their input for a username or password is invalid, but all of the answers I have seen so far are not very helpful. I have found "^[a-zA-Z0-9]*$" to be the most useful so far for detecting special characters such as asterisks and periods, but it seems to only work when a user uses all of the characters above instead of just the ones within the range of characters that satisfy the requirement. I will show my code below:

 while not chosen_user:
     chosen_user = input("""Enter the username that you would like. Please keep it between 6 and 15 
     characters. Do not use special characters such as '&', '@', or '!' in your username. Underscores are allowed.\n>""")
    if (len(chosen_user) >= 6 or len(chosen_user) <= 15) and "^[a-zA-Z0-9_]*$" in chosen_user:
        chosen_user = True
        usernames_passwords[chosen_user] = ''
    else:
        print('Username does not meet the requirements. Please try again.')
        chosen_user = False
 while not chosen_pass:
     chosen_pass = input("""Enter a password that contains no special characters. Password must be at 
        least 6 characters.\n>""")
        if len(chosen_pass) >= 6 and "^[a-zA-Z0-9]*$" in chosen_pass:
            chosen_pass = True
            usernames_passwords[chosen_user] = chosen_pass
        else:
            print('Password is invalid. Please try again.')
            chosen_pass = False

I cannot figure out how to get a password approved while only using some of the characters, and I have been struggling for a while. Any help would be nice.

**Also, keep in mind that I am in high school and would prefer to keep this code as simple as possible. Imports are okay, but I would like to understand how and when to use these things for future use. Thanks!!

Answer 1

Try this:

import re #--> import regular expressions module

while not chosen_user:
    chosen_user = input("""Enter the username that you would like. Please keep it between 6 and 15
    characters. Do not use special characters such as '&', '@', or '!' in your username. Underscores are allowed.\n>""")
    if (len(chosen_user) >= 6 and len(chosen_user) <= 15) and re.search(r"^[A-Za-z0-9_]+$", chosen_user):
        chosen_user = True
        usernames_passwords[chosen_user] = ''
    else:
        print('Username does not meet the requirements. Please try again.')
        chosen_user = False

while not chosen_pass:
    chosen_pass = input("""Enter a password that contains no special characters. Password must be at 
    least 6 characters.\n>""")
    if len(chosen_pass) >= 6 and re.search(r"^[A-Za-z0-9_]+$", chosen_pass):
        chosen_pass = True
        usernames_passwords[chosen_user] = chosen_pass
    else:
        print('Password is invalid. Please try again.')
        chosen_pass = False

Answer 2

You can simplify your looping logic and also your string checking by using regular expressions:

import re

chosen_user = input("""Enter the ... allowed.\n>""")
while not re.match(r"^\w{6,15}$", chosen_user, flags=re.ASCII):
    chosen_user = input('Username does not meet the requirements. Please try again.')

chosen_pass = input("""Enter a password ... least 6 characters.\n>""")
while not re.match(r"^[a-zA_Z]{6,}$", chosen_pass):
    chosen_pass = input('Password is invalid. Please try again.')

You will find in the re docs :

"^"
(Caret.) Matches the start of the string, and in MULTILINE mode also matches immediately after each newline.

"$"
Matches the end of the string [...].

"\\w"
Matches Unicode word characters; this includes most characters that can be part of a word in any language, as well as numbers and the underscore. If the ASCII flag is used, only [a-zA-Z0-9_] is matched.

"{m,n}"
Causes the resulting RE to match from m to n repetitions of the preceding RE, attempting to match as many repetitions as possible. For example, a{3,5} will match from 3 to 5 'a' characters. Omitting m specifies a lower bound of zero, and omitting n specifies an infinite upper bound.

Answer 3

 while not chosen_user:
     chosen_user = input("""Enter the username that you would like. Please keep it between 6 and 15 
     characters. Do not use special characters such as '&', '@', or '!' in your username. Underscores are allowed.\n>""")
    if (len(chosen_user) >= 6 or len(chosen_user) <= 15) and "^[a-zA-Z0-9_]*$" in chosen_user:
        chosen_user = True
        usernames_passwords[chosen_user] = ''
    else:
        print('Username does not meet the requirements. Please try again.')
        chosen_user = False
 while not chosen_pass:
     pas = input("""Enter a password that contains no special characters. Password must be at 
        least 6 characters.\n>""")
        schar="@_!#$%^&*()<>?/\|}{~:]"
        if len(pas)>=6:
           for i in pas:
               if i in schar:
                   choosen_pass=True
                   break
            usernames_passwords[chosen_user] = chosen_pass
        else:
            print('Password is invalid. Please try again.')
            chosen_pass = False