Python fnmatch Module

The fnmatch module in Python provides support for Unix shell-style wildcards to match filenames. It offers simple functions to compare filenames against a pattern, making it useful for filtering file names based on patterns.

Table of Contents

1. Introduction
2. Key Functions
   • fnmatch
   • fnmatchcase
   • filter
   • translate
3. Wildcards
   • *
   • ?
   • []
4. Examples
   • Basic Usage
   • Case-Sensitive Matching
   • Filtering File Lists
5. Real-World Use Case
6. Conclusion
7. References

Introduction

The fnmatch module is used to compare filenames against a pattern. It supports Unix shell-style wildcards, which makes it easier to filter and match filenames in a directory or list.

Key Functions

fnmatch

Checks if a filename matches a pattern. The comparison is case-insensitive on Windows and case-sensitive on Unix.

import fnmatch

print(fnmatch.fnmatch('example.txt', '*.txt'))  # True
print(fnmatch.fnmatch('example.TXT', '*.txt'))  # True on Windows, False on Unix

fnmatchcase

Performs a case-sensitive comparison, regardless of the operating system.

import fnmatch

print(fnmatch.fnmatchcase('example.txt', '*.TXT'))  # False
print(fnmatch.fnmatchcase('example.TXT', '*.TXT'))  # True

filter

Filters a list of filenames to include only those that match a pattern.

import fnmatch

filenames = ['file1.txt', 'file2.txt', 'file3.py', 'script.py']
print(fnmatch.filter(filenames, '*.py'))  # ['file3.py', 'script.py']

translate

Returns a string containing the regex pattern equivalent to the wildcard pattern.

import fnmatch

pattern = fnmatch.translate('*.txt')
print(pattern)  # '.*\\.txt\\Z(?ms)'

Wildcards

*

Matches zero or more characters.

import fnmatch

print(fnmatch.fnmatch('file.txt', '*.txt'))  # True
print(fnmatch.fnmatch('file.txt', '*.*'))    # True

?

Matches exactly one character.

import fnmatch

print(fnmatch.fnmatch('file.txt', 'f?le.txt'))  # True
print(fnmatch.fnmatch('file.txt', 'f?le.tx?'))  # True

[]

Matches any one of the enclosed characters.

import fnmatch

print(fnmatch.fnmatch('file.txt', '[fF]ile.txt'))  # True
print(fnmatch.fnmatch('File.txt', '[fF]ile.txt'))  # True
print(fnmatch.fnmatch('file.txt', '[a-z]ile.txt')) # True

Examples

Basic Usage

import fnmatch

filename = 'data.csv'
pattern = '*.csv'

if fnmatch.fnmatch(filename, pattern):
    print(f"{filename} matches the pattern {pattern}")

Case-Sensitive Matching

import fnmatch

filename = 'Data.CSV'
pattern = '*.CSV'

if fnmatch.fnmatchcase(filename, pattern):
    print(f"{filename} matches the pattern {pattern} (case-sensitive)")
else:
    print(f"{filename} does not match the pattern {pattern} (case-sensitive)")

Filtering File Lists

import fnmatch

filenames = ['data1.csv', 'data2.txt', 'data3.csv', 'report.doc']
csv_files = fnmatch.filter(filenames, '*.csv')

print(f"CSV files: {csv_files}")  # ['data1.csv', 'data3.csv']

Real-World Use Case

Finding Log Files

import fnmatch
import os

log_dir = '/path/to/logs'
pattern = '*.log'

log_files = [f for f in os.listdir(log_dir) if fnmatch.fnmatch(f, pattern)]

for log_file in log_files:
    print(f"Processing log file: {log_file}")
    # Perform processing on the log file

Conclusion

The fnmatch module in Python provides a simple and effective way to match filenames using Unix shell-style wildcards. It is useful for filtering and finding files based on patterns, making it a handy tool for file manipulation tasks.

References

• Python fnmatch module documentation