How To Check If All Elements In A List Are Strings Python

Checking if all elements in a list are strings is a common operation when working with lists in Python.

This operation is usually required when validating user inputs, parsing data from files, or handling input from other functions in the code. In this tutorial, you will learn how to check if all elements in a Python list are strings using different approaches.

By the end, you will be able to choose the method that best suits your needs and apply it to your projects.

1. Using a for loop

The first and most straightforward approach is to use a for loop to iterate through the list and check if each element is an instance of the str class using the isinstance() function. The loop will break if a non-string element is found.

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def all_strings(elements):
    for element in elements:
        if not isinstance(element, str):
            return False
    return True

2. Using a list comprehension

A more Pythonic way to achieve the same result is to use a list comprehension. In this method, we create a new list that contains boolean values for each element, indicating whether it is a string or not. We then use the all() built-in function to check if all the boolean values in the new list are true.

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def all_strings(elements):
    return all([isinstance(element, str) for element in elements])

3. Using a generator expression

A more efficient method is to use a generator expression instead of a list comprehension.

The generator expression is similar to a list comprehension, but it does not build a new list in memory. Instead, it creates a generator object that generates the boolean values on-the-fly, which is then consumed by the all() function.

This method is recommended when working with large lists, as it consumes less memory and is generally faster.

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def all_strings(elements):
    return all(isinstance(element, str) for element in elements)

Full code

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def all_strings_for_loop(elements):
    for element in elements:
        if not isinstance(element, str):
            return False
    return True
 
def all_strings_list_comprehension(elements):
    return all([isinstance(element, str) for element in elements])
 
def all_strings_generator_expression(elements):
    return all(isinstance(element, str) for element in elements)
 
elements = ['Hello', 'World', 123, 'Python']
print(all_strings_for_loop(elements))  # Output: False
print(all_strings_list_comprehension(elements))  # Output: False
print(all_strings_generator_expression(elements))  # Output: False
 
elements = ['Hello', 'World', 'Python']
print(all_strings_for_loop(elements))  # Output: True
print(all_strings_list_comprehension(elements))  # Output: True
print(all_strings_generator_expression(elements))  # Output: True

Output

False
False
False
True
True
True

Conclusion

In this tutorial, you learned how to check if all elements in a Python list are strings using three different methods: a for loop, a list comprehension, and a generator expression.

The generator expression is recommended for large lists due to its memory and performance efficiency. However, choosing the right method depends on your specific use case and coding style preferences.