check if a string only contains specific characters? [duplicate]

Question

I need to check a string (password validator) whether it contains specific characters and lenght in python. One of the condition is, that the string pwd only contains the characters a-z, A-Z, digits, or the special chars "+", "-", "*", "/".

Blockquote

These utilities should help me solve it (but I don't get it):

• Use isupper/islower to decide whether a string is upper case or lower case
• Use isdigit to check if it is a number
• Use the in operator to check whether a specific character exists in a string.

pwd = "abc"

def is_valid():
    # You need to change the following part of the function
    # to determine if it is a valid password.
    validity = True

    # You don't need to change the following line.
    return validity

# The following line calls the function and prints the return
# value to the Console. This way you can check what it does.
print(is_valid())

I'd appreciate your help!

Answer 1

We can use re.search here for a regex option:

def is_valid(pwd):
    return re.search(r'^[A-Za-z0-9*/+-]+$', pwd) is not None

print(is_valid("abc"))   # True
print(is_valid("ab#c"))  # False

Answer 2

You could use a regex, but as the task only involves checking that characters belong to a set, it might be more efficient to just use python sets:

def is_valid(pwd):
    from string import ascii_letters
    chars = set(ascii_letters+'0123456789'+'*-+/')
    return all(c in chars for c in pwd)

examples:

>>> is_valid('abg56*-+')
True

>>> is_valid('abg 56*')
False

Alternative using a regex:

def is_valid(pwd):
    import re
    return bool(re.match(r'[a-zA-Z\d*+-/]*$', pwd))