How to Check if a String Ends with a File Extension in Python

This code checks whether a filename ends with any of a list of file extensions, handling case insensitivity.

Easy Python 3.9+ Aug 9, 2026 Strings & text 17 views 0 copies

file-extension string-methods endswith case-insensitive

Python code

13 lines

Python 3.9+

def ends_with_extension(filename, extensions):
    """Check if a filename ends with any of the given extensions."""
    lower_name = filename.lower()
    return any(lower_name.endswith(ext.lower()) for ext in extensions)

if __name__ == "__main__":
    # Test cases
    test_files = ["report.pdf", "image.PNG", "script.py", "notes.txt", "archive.tar.gz"]
    extensions = [".pdf", ".png", ".py"]
    
    for file in test_files:
        result = ends_with_extension(file, extensions)
        print(f"{file:20} -> {result}")

Output

stdout

report.pdf          -> True
image.PNG          -> True
script.py          -> True
notes.txt          -> False
archive.tar.gz     -> False

How it works

The endswith method checks if a string ends with a specified suffix. By converting both the filename and each extension to lowercase using .lower(), the check becomes case-insensitive. The any() function returns True if at least one extension matches, otherwise False. This approach is simple and efficient for a small list of extensions.

Common mistakes

Forgetting to convert both filename and extension to lowercase, causing case-sensitive mismatches.
Not including the leading dot in extensions (e.g., using 'pdf' instead of '.pdf').
Checking only one extension with `endswith` instead of iterating over a list.

Variations

Use `os.path.splitext` to extract the extension and compare against a set.
Use a regular expression to match a pattern of allowed extensions.

Real-world use cases

Filtering uploaded files in a web application to only allow certain file types.
Validating file extensions before processing in a batch data pipeline.
Checking downloaded files to ensure they have the expected format before parsing.

How to Check if a String Ends with a File Extension in Python

Python code

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How it works

Common mistakes

Variations

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