Python fnmatch.fnmatch() Function: Usage and Examples

This Python tutorial explains fnmatch.fnmatch() Function: Usage and Examples. Follow the example, inspect the output, and practise an input change so you understand the behavior rather than simply copying the syntax.

What This Feature Does

Compare one filename against a Unix-style wildcard pattern with fnmatch.fnmatch().

fnmatch.fnmatch(name, pattern) matches one string without performing a filesystem search. Matching case is normalized using os.path.normcase(), so the result may differ across platforms; use fnmatchcase() for case-sensitive matching.

When to Use It

This technique belongs to file copying, temporary files and matching. It is useful when the input, operation and expected outcome are known. Start with a small controlled example before integrating it into a larger workflow.

Step-by-Step Python Example

Read the code once before running it. Notice which values are inputs, which function or method performs the work, and whether the result is returned or stored by changing an existing object.

import fnmatch

print(fnmatch.fnmatch("report.csv", "*.csv"))
print(fnmatch.fnmatch("report.txt", "*.csv"))

Understanding the Code

First, the imports make fnmatch available. They provide the filesystem, data or standard-library functions used later.
Find the call fnmatch.fnmatch("report.csv", "*.csv"). Its parameters determine the specific operation demonstrated in the title.
Its purpose is to compare one filename against a unix-style wildcard pattern with fnmatch.fnmatch(). Compare this description against the result printed by the program.
The print() expressions display a checkable outcome. Print values and exception names are not substitutes for the program result itself.

Expected Output

True
False

Each printed line corresponds to a separate observation in the program. Use the lines to distinguish returned data, changes to existing objects, and status checks.

Important Details and Edge Cases

fnmatchcase() avoids platform-dependent case normalization.

Before applying this to real documents, check whether the method reads data, creates a new file, moves it, or overwrites an existing file. Work in a disposable test directory first and handle OSError-related failures in applications.

Practice: Try It Yourself

Test whether several filenames match an *.json pattern.

Begin by copying the example into a separate practice file. Change one input at a time, run it again, and describe why the result changed. If the exercise writes or deletes files, keep it inside a temporary test folder.

Official Python Documentation

For the complete reference, see the Python standard library documentation.

Common Beginner Mistakes

Expecting fnmatch() to find files on disk instead of matching one supplied string.
Assuming case sensitivity is identical across Windows and POSIX systems.
Before applying this to real documents, check whether the method reads data, creates a new file, moves it, or overwrites an existing file. Work in a disposable test directory first and handle OSError-related failures in applications.

Key Takeaways

Compare one filename against a Unix-style wildcard pattern with fnmatch.fnmatch().
fnmatch.fnmatch(name, pattern) matches one string without performing a filesystem search. Matching case is normalized using os.path.normcase(), so the result may differ across platforms; use fnmatchcase() for case-sensitive matching.
Avoid this common pitfall: Expecting fnmatch() to find files on disk instead of matching one supplied string.