Text data can contain alphabets numbers, spaces and special characters such as and

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Given a string, we have to find whether the string contains any letters, numbers, underscores, and dashes or not. It is usually used for verifying username and password validity. For example, the user has a string for the username of a person and the user doesn’t want the username to have any special characters such as @, $, etc. 

Prerequisite: Regular Expression in Python

Let’s see the different methods for solving this task:

Method 1: Using Regular Expression.

There is a function in the regular expression library(re) that compares two strings for us. re.match(pattern, string) is a function that returns an object, to find whether a match is find or not we have to typecast it into boolean. 

Syntax: 

re.match(pattern, string) 

Parameters:

• pattern: the pattern against which you want to check 
• string: the string you want to check for the pattern 

Return: Match object 

Let’s see an example:

Example 1:

Python3

import re

pattern = "^[A-Za-z0-9_-]*$"

string = "G33ks_F0r_Geeks"

state = bool(re.match(pattern, string))

print(state)

Output:

True

Example 2:

Python3

import re

print(bool(re.match("^[A-Za-z0-9_-]*$",

                    'ValidString12-_')))

print(bool(re.match("^[A-Za-z0-9_-]*$",

                    'inv@lidstring')))

Output:

True
False

Method 2: Using Set.

Set is a built-in data type in Python. We are usingissubset()function of a set that returns True if all characters of a set are present in a given set Otherwise False.

Syntax: 

set_name.issubset(set)

Parameters: 

• set: Represents that set in which the subset has to be searched 

Return: boolean value

Let’s see an example:

Example 1: 

Python3

allowed_chars = set(

    ("0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ_-"))

string = "inv@lid"

validation = set((string))

if validation.issubset(allowed_chars):

    print("True")

else:

    print("False")

Output:

False

Example 2: 

Python3

allowed_chars = set(

    "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ_-")

string = "__Val1d__"

validation = set((string))

if validation.issubset(allowed_chars):

    print("True")

else:

    print("False")

Output:

True

The Time and Space Complexity for all the methods are the same:

Time Complexity: O(n)

Auxiliary Space: O(n)

Method : Using replace() and len() methods

Python3

allowed_chars = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ_-"

string = "__Val1d__"

for i in allowed_chars:

    string = string.replace(i, "")

if len(string) == 0:

    print("True")

else:

    print("False")