Python: How to check for specific characters inside a string from another string

Question

I am coding a simple program in which I would like to have the user input a string and then my code will check from another string of characters (that are not allowed in the string).

The string of characters that are not allowed are:

invalidChar = (@,#,£,{,[,},],:,;,",',|,\,/,?,~,`)

For example, if the user inputs "testing@3testing" I would like the code to tell the user that there is a character in the input that is not allowed.

The way I originally thought was to use:

if password[i]=="@":
  booleanCheck = True

but this would have to be repeated several times over and this would make for messy code.

Thanks in advance!

You can use a set of chars for this, eg `set("@#£{[}]:;\"'|\\/?~`")` — PM 2Ring, Oct 02 '17 at 18:03

score 0 · Answer 1 · answered Oct 02 '17 at 18:05

You can test a character against a list of characters like this:

invalidChar = ['@','#','£','{','[','}',']',':',';','"','\'','|',
               '\\','/','?','~','`']

input_string = 'testing@3testing'

# Let's define our logic in a function so that we can use it repeatedly
def contains_invalid_char(s):  # here we name our input string s
    for element in s:          # lets iterate through each char in s
        if element in invalidChar:  # If its in the set, do the block
            return True
    return False               # If we made it this far, all were False

# Then you can use the method to return a True or False, to use in a conditional or a print statement or whatever, like

if contains_invalid_char(input_string):
    print("It was a bad string")

score 0 · Answer 2 · answered Oct 02 '17 at 18:05

Make a set of invalid characters, and then check each character in your password against that set.

def has_invalid(password):
    invalidChar = set(['@','#','£','{','[','}',']',':',';','"','\'','|','\\','/','?','~','`'])
    return any(char in invalidChar for char in password)

Note that some of the characters need to be escaped

score 0 · Answer 3 · answered Oct 02 '17 at 18:07

0

You can do something like this:

>>> invalidChar = ('@','#')
>>> password ="testing@3testing"
>>> if any(ch in password for ch in invalidChar):
    booleanCheck = True

>>> booleanCheck
True

answered Oct 02 '17 at 18:07

Tabaene Haque

576
2
10

No need for the if statement - you could just do `booleanCheck = any(....)` – Wondercricket Oct 02 '17 at 18:09
Yes. you are right. Thanks @Wondercricket for you comment – Tabaene Haque Oct 02 '17 at 18:13

Python: How to check for specific characters inside a string from another string

3 Answers3