Python check if string contains characters

How to Check if a String Contains Special Characters in Python

Here, we will develop Programs for How to check if a string contains special characters in Python. A special character is a character that is not an alphabetic or numeric character. Non-alphabetic or non-numeric character, such as @, #, $, %, &, * and +. We are going to write a program that checks whether a string contains any special character or not using various methods.

How to Check Special Characters in Python

We will first import the required package from the Python library and take a string while declaring the variables. Then, check the presence of special characters and pass it into the search function. The search function matches all the characters of the string to the set of special characters. If there is a match then it returns the matched character otherwise it will return None.

# Python program to check special character # import required package import re # take inputs string = input('Enter any string: ') # special characters special_char = re.compile('[@_!#$%^&*()<>?/\|><~:]') # check string contains special characters or not if(special_char.search(string) == None): print('String does not contain any special characters.') else: print('The string contains special characters.')

Enter any string: @knowprogram
The string contains special characters.

Enter any string: Know Program
String does not contain any special characters.

Enter any string: $25
The string contains special characters.

How to Identify Special Characters in Python

We are using the re.match() function to check whether a string contains any special character or not. The re.match() method returns a match when all characters in the string are matched with the pattern and None if it’s not matched.

# Python program to check special character # import required package import re # take inputs string = input('Enter any string: ') # check string contains special characters or not if(bool(re.match('^[a-zA-Z0-9]*$', string)) == True): print('String does not contain any special characters.') else: print('The string contains special characters.')

Enter any string: [email protected]The string contains special characters.

How to Check if a String Contains Special Characters in Python

In the above program, we used the re.match() method but in this program, we are using the re.search() method. This is also a function in the RegEx module. The re.search() function locates a match anywhere in the string.

# Python program to check special character # import required package import re # take inputs string = input('Enter any string: ') # check string contains special characters or not if(bool(re.search('^[a-zA-Z0-9]*$', string)) == True): print('String does not contain any special characters.') else: print('The string contains special characters.')

Enter any string: Python
String does not contain any special characters.

Function to Check Special Characters in Python

Function to check special Characters. The string.punctuation is pre-defined in the string module of Python3. It contains all the characters as a string. This returns all sets of punctuation.

# Python program to check special character # importing string function import string # take inputs ch = input('Enter any string: ') # special characters invalid_char = set(string.punctuation) # check string contains special characters or not if any(char in invalid_char for char in ch): print('String does not contain any special characters.') else: print('The string contains special characters.')

Enter any string: string.punctuation
The string contains special characters.

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Python How to Check If String Contains Characters from a List

To check if a Python string contains all the characters from a list, check if each character exists in the word:

chars = ["H", "e", "y"] word = "Hello" has_all = all([char in word for char in chars]) print(has_all)

To learn other useful string methods in Python, feel free to check this article.

Below you find a more detailed guide of how to check if a string contains characters from a list.

Step-by-step Guide

Given a list of characters and a string, you can check if all the characters of a list are found in the target string following these steps:

1. Loop through the list of characters.
2. Check if a character is in the target string.
3. Add the truth to a list.
4. Check if all truth values in a list are True.

Here is how it looks in code:

chars = ["H", "e", "y"] word = "Hello" truths = [] # 1. Loop through the chars for char in chars: # 2. Check if a character is in the target string truth = char in word # 3. Add the truth to a truths list truths.append(truth) # 4. Check if all boolean values are True has_all = True for truth in truths: has_all = has_all and truth print(has_all)

But you can make this piece of code shorter by using:

• List comprehension to shorten the 1st for loop.
• Built-in all() method to get rid of the 2nd loop. This method checks if all booleans are True.

This makes the code look the same as in the example solution in the introduction:

chars = ["H", "e", "y"] word = "Hello" has_all = all([char in word for char in chars]) print(has_all)

To be more general, you can implement a function that gets the job done.

Here is how it looks in code:

def has_all(chars, string): return all([char in string for char in chars]) # Example call print(has_all("Hello", ["H","i"]))

Conclusion

Today you learned how to check if a Python string contains all characters present in a list.

To recap, you need to run a loop through the list of the characters. Then you need to check if each of those characters exists in the target string.

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Check If String Contains Only Certain Characters in Python

In this tutorial, we will look at how to check if a string contains only certain characters in Python with the help of some examples.

How to check if a string contains only certain characters?

You can use a combination of the all() function and the membership operator, in to check if a string contains only certain characters in Python. Use the following steps –

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1. Create a set (or a string) containing the allowed characters.
2. Iterate through the characters in the string and use the membership operator "in" to check if the character is in the allowed set of characters.
3. Use the Python built-in all() function to return True only if all the characters in the string are present in the allowed characters.

# string s = "ababaaaab" # string with only allowed characters allowed_s = "ab" # check if s contains only allowed characters print(all(ch in allowed_s for ch in s))

Here, we get True as the output because all the characters in the string s are present in the allowed characters.

Let’s look at another example.

# string s = "abcbaaaab" # string with only allowed characters allowed_s = "ab" # check if s contains only allowed characters print(all(ch in allowed_s for ch in s))

Here, we get False as the output because the character “c” is not in the allowed characters.

We can modify the allowed characters string to suit our specific use case. For example, if you want to check if the string contains only digits you can use “0123456789” as your allowed characters string.

# string s = "1150" # string with only allowed characters allowed_s = "0123456789" # check if s contains only allowed characters print(all(ch in allowed_s for ch in s))

Note that for the above use case, you can also just directly use the string isdigit() function.

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Author

Piyush is a data professional passionate about using data to understand things better and make informed decisions. He has experience working as a Data Scientist in the consulting domain and holds an engineering degree from IIT Roorkee. His hobbies include watching cricket, reading, and working on side projects. View all posts

Data Science Parichay is an educational website offering easy-to-understand tutorials on topics in Data Science with the help of clear and fun examples.

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Python: Check if String Contains Substring

Checking whether a string contains a substring aids to generalize conditionals and create more flexible code. Additionally, depending on your domain model - checking if a string contains a substring may also allow you to infer fields of an object, if a string encodes a field in itself.

In this guide, we'll take a look at how to check if a string contains a substring in Python.

The in Operator

The easiest way to check if a Python string contains a substring is to use the in operator.

The in operator is used to check data structures for membership in Python. It returns a Boolean (either True or False ). To check if a string contains a substring in Python using the in operator, we simply invoke it on the superstring:

fullstring = "StackAbuse" substring = "tack" if substring in fullstring: print("Found!") else: print("Not found!") 

This operator is shorthand for calling an object's __contains__ method, and also works well for checking if an item exists in a list. It's worth noting that it's not null-safe, so if our fullstring was pointing to None , an exception would be thrown:

TypeError: argument of type 'NoneType' is not iterable 

To avoid this, you'll first want to check whether it points to None or not:

fullstring = None substring = "tack" if fullstring != None and substring in fullstring: print("Found!") else: print("Not found!") 

The String.index() Method

The String type in Python has a method called index() that can be used to find the starting index of the first occurrence of a substring in a string.

If the substring is not found, a ValueError exception is thrown, which can be handled with a try-except-else block:

fullstring = "StackAbuse" substring = "tack" try: fullstring.index(substring) except ValueError: print("Not found!") else: print("Found!") 

This method is useful if you also need to know the position of the substring, as opposed to just its existence within the full string. The method itself returns the index:

print(fullstring.index(substring)) # 1 

Though - for the sake of checking whether a string contains a substring, this is a verbose approach.

The String.find() Method

The String class has another method called find() which is more convenient to use than index() , mainly because we don't need to worry about handling any exceptions.

If find() doesn't find a match, it returns -1, otherwise it returns the left-most index of the substring in the larger string:

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fullstring = "StackAbuse" substring = "tack" if fullstring.find(substring) != -1: print("Found!") else: print("Not found!") 

Naturally, it performs the same search as index() and returns the index of the start of the substring within the parent string:

print(fullstring.find(substring)) # 1 

Regular Expressions (RegEx)

Regular expressions provide a more flexible (albeit more complex) way to check strings for pattern matching. With Regular Expressions, you can perform flexible and powerful searches through much larger search spaces, rather than simple checks, like previous ones.

Python is shipped with a built-in module for regular expressions, called re . The re module contains a function called search() , which we can use to match a substring pattern:

from re import search fullstring = "StackAbuse" substring = "tack" if search(substring, fullstring): print "Found!" else: print "Not found!" 

This method is best if you are needing a more complex matching function, like case insensitive matching, or if you're dealing with large search spaces. Otherwise the complication and slower speed of regex should be avoided for simple substring matching use-cases.

About the Author

This article was written by Jacob Stopak, a software consultant and developer with passion for helping others improve their lives through code. Jacob is the creator of Initial Commit - a site dedicated to helping curious developers learn how their favorite programs are coded. Its featured project helps people learn Git at the code level.

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