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List string in Python

In this article, well take a look at how we can find a string in a list in Python.

Find a String in a List in Python

There are various approaches to this problem, from the ease of use to efficiency.

Using the in operator

We can use Pythons in operator to find a string in a list in Python. This takes in two operands a and b, and is of the form:

ret_value = a in b

Here, ret_value is a boolean, which evaluates to True if a lies inside b, and False otherwise.

We can directly use this operator in the following way:

a = [1, 2, 3] b = 4 if b in a: print['4 is present!'] else: print['4 is not present']

Output

4 is not present

We can also convert this into a function, for ease of use.

def check_if_exists[x, ls]: if x in ls: print[str[x] + ' is inside the list'] else: print[str[x] + ' is not present in the list'] ls = [1, 2, 3, 4, 'Hello', 'from', 'AskPython'] check_if_exists[2, ls] check_if_exists['Hello', ls] check_if_exists['Hi', ls]

Output

2 is inside the list Hello is inside the list Hi is not present in the list

This is the most commonly used, and recommended way to search for a string in a list. But, for illustration, well show you other methods as well.

Using List Comprehension

Lets take another case, where you wish to only check if the string is a part of another word on the list and return all such words where your word is a sub-string of the list item.

Consider the list below:

ls = ['Hello from AskPython', 'Hello', 'Hello boy!', 'Hi']

If you want to search for the substring Hello in all elements of the list, we can use list comprehensions in the following format:

ls = ['Hello from AskPython', 'Hello', 'Hello boy!', 'Hi'] matches = [match for match in ls if "Hello" in match] print[matches]

This is equivalent to the below code, which simply has two loops and checks for the condition.

ls = ['Hello from AskPython', 'Hello', 'Hello boy!', 'Hi'] matches = [] for match in ls: if "Hello" in match: matches.append[match] print[matches]

In both cases, the output will be:

['Hello from AskPython', 'Hello', 'Hello boy!']

As you can observe, in the output, all the matches contain the string Hello as a part of the string. Simple, isnt it?

Using the any[] method

In case you want to check for the existence of the input string in any item of the list, We can use the any[] method to check if this holds.

For example, if you wish to test whether AskPython is a part of any of the items of the list, we can do the following:

ls = ['Hello from AskPython', 'Hello', 'Hello boy!', 'Hi'] if any["AskPython" in word for word in ls]: print['\'AskPython\' is there inside the list!'] else: print['\'AskPython\' is not there inside the list']

Output

'AskPython' is there inside the list!

Using filter and lambdas

We can also use the filter[] method on a lambda function, which is a simple function that is only defined on that particular line. Think of lambda as a mini function, that cannot be reused after the call.

ls = ['Hello from AskPython', 'Hello', 'Hello boy!', 'Hi'] # The second parameter is the input iterable # The filter[] applies the lambda to the iterable # and only returns all matches where the lambda evaluates # to true filter_object = filter[lambda a: 'AskPython' in a, ls] # Convert the filter object to list print[list[filter_object]]

Output

['Hello from AskPython']

We do have what we expected! Only one string matched with our filter function, and thats indeed what we get!

Conclusion

In this article, we learned about how we can find a string with an input list with different approaches. Hope this helped you with your problem!

References

JournalDev article on finding a string in a List
StackOverflow question on finding a string inside a List

Find a String in a List in Python

Using the in operator

Using List Comprehension

Using the any[] method

Using filter and lambdas

Conclusion

References

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