5 Best Ways to Perform Unix Filename Pattern Matching in Python

πŸ’‘ Problem Formulation: In Python, you may come across situations where you need to filter or match filenames in a directory based on Unix-like patterns. For example, you may want to find all files ending with .txt or starting with log_ in a certain path. It is crucial to know the efficient methods for such pattern matching to get the desired set of filenames as output.

Method 1: Using the glob Module

The glob module in Python provides functions to create lists of files matching specified patterns according to Unix shell rules, such as wildcards and character ranges. Its main function is glob.glob(), which returns a list of pathnames that match the pattern.

Here’s an example:

import glob

file_list = glob.glob('/path/to/files/*.txt')
print(file_list)

Output:

['/path/to/files/document1.txt', '/path/to/files/document2.txt']

This code snippet finds all files ending with .txt within the specified directory. The pattern used here includes the wildcard *, which matches any number of characters.

Method 2: Using fnmatch Module

Python’s fnmatch module provides support for Unix filename pattern matching. The fnmatch.fnmatch() function matches a single file name against the pattern, which can be helpful when filtering filenames in a list.

Here’s an example:

import fnmatch
import os

filenames = os.listdir('/path/to/files/')
matches = [f for f in filenames if fnmatch.fnmatch(f, '*.txt')]
print(matches)

Output:

['document1.txt', 'document2.txt']

In this example, we first obtain a list of filenames in a directory and then filter this list to include only those that match the pattern *.txt.

Method 3: Using pathlib Module

The pathlib module in Python represents filesystem paths with semantics appropriate for different operating systems. The Path.glob() function allows pattern matching on files in a concise and readable manner.

Here’s an example:

from pathlib import Path

path = Path('/path/to/files/')
file_list = list(path.glob('*.txt'))
print(file_list)

Output:

[PosixPath('/path/to/files/document1.txt'), PosixPath('/path/to/files/document2.txt')]

This code snippet uses the pathlib.Path object to match all files with a .txt extension. The glob() method is called on a Path object to perform the pattern matching.

Method 4: Using os Module with List Comprehension

Unix filename pattern matching can be manually implemented using Python’s built-in os module to list files in a directory and list comprehension to filter them based on a simple pattern.

Here’s an example:

import os

filenames = [f for f in os.listdir('/path/to/files/') if f.endswith('.txt')]
print(filenames)

Output:

['document1.txt', 'document2.txt']

This snippet lists all files in the chosen directory and uses list comprehension with str.endswith() to match the filenames that have a .txt extension.

Bonus One-Liner Method 5: Using a Generator Expression with os.listdir()

A concise method to filter Unix filenames in Python is by using a generator expression along with the os.listdir() function. This uses minimal memory and is suitable for large directories.

Here’s an example:

import os

file_gen = (f for f in os.listdir('/path/to/files') if f.endswith('.txt'))
for file in file_gen:
    print(file)

Output:

document1.txt
document2.txt

Here we create a generator that will yield all filenames ending with .txt as we iterate over it. It’s memory efficient and gets the job done with very little code.

Summary/Discussion

  • Method 1: Using the glob Module. Direct and concise for simple wildcard patterns. May not perform well with very large sets of files due to returning a list.
  • Method 2: Using fnmatch Module. Offers more flexibility in matching patterns. Requires additional code to list directory contents.
  • Method 3: Using pathlib Module. Modern and object-oriented approach, easy-to-read code. Requires Python 3.4 and above.
  • Method 4 Using os Module with List Comprehension. Great for simple suffix or prefix checking. Not a full pattern matching solution.
  • Bonus One-Liner Method 5: Using a Generator Expression with os.listdir(). Extremely memory-efficient, good for very large directories, but limited to simple checks.