Check if string contains characters python

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

Here is an example:

chars = ["H", "e", "y"]
word = "Hello"

has_all = all[[char in word for char in chars]]

print[has_all]

Output:

False

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]

Output:

False

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]

Output:

False

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"]]]

Output:

False

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.

Thanks for reading.

Happy coding!

Further Reading

50 Python Interview Questions

In this guide, we'll take a look at how to check if a string contains a substring in Python. As usual, each approach we'll cover has different pros and cons.

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.

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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 need to know the position of the substring, as opposed to just its existence within the full string.

The String.find[] Method

The String type has another method called find which is more convenient to use than index[], 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.

fullstring = "StackAbuse"
substring = "tack"

if fullstring.find[substring] != -1:
    print["Found!"]
else:
    print["Not found!"]

If you'd prefer to avoid the need to catch errors, then this method should be favored over index[].

Regular Expressions [RegEx]

Regular expressions provide a more flexible [albeit more complex] way to check strings for pattern matching. 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. Otherwise the complication and slower speed of regex should be avoided for simple substring matching use-cases.

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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