π‘ Problem Formulation: When working in a UNIX-like environment or dealing with file systems, it is common to encounter the need for filename pattern matching. This could involve, for example, finding all files with the ‘.txt’ extension in a directory. Users often desire a simple yet powerful method to filter filenames that match a particular patternβusing glob-like rules as seen in shell scripting. We seek Pythonic methods to achieve this, where input includes filenames, and output is a filtered list matching our criteria.
Method 1: Using fnmatch.fnmatch
This method utilizes the fnmatch.fnmatch
function from the fnmatch
module which compares a single filename to a pattern and returns a boolean indicating a match. The patterns follow the same rules as the UNIX shell.
Here’s an example:
import fnmatch import os # List of filenames filenames = ['data1.txt', 'data2.csv', 'image.png', 'report.txt', 'summary.pdf'] # Pattern to match pattern = '*.txt' # Filtering filenames matched_files = [f for f in filenames if fnmatch.fnmatch(f, pattern)] print(matched_files)
Output:
['data1.txt', 'report.txt']
This code snippet iterates over a list of filenames and applies the fnmatch.fnmatch
function to each filename with the given pattern. Files ending with ‘.txt’ are matched and added to the matched_files
list, which is printed as the output.
Method 2: Using fnmatch.filter
The fnmatch.filter
function takes a list of filenames and a pattern, returning a list of filenames that match the pattern. Unlike fnmatch.fnmatch
, filter
processes a list of names and is typically more concise for bulk operations.
Here’s an example:
import fnmatch # List of filenames filenames = ['data1.txt', 'data2.csv', 'image.png', 'report.txt', 'summary.pdf'] # Pattern to match pattern = '*.txt' # Get matched filenames matched_files = fnmatch.filter(filenames, pattern) print(matched_files)
Output:
['data1.txt', 'report.txt']
This code snippet uses fnmatch.filter
to directly obtain the list of filenames that match the provided UNIX shell-style pattern. No need for a list comprehension.
Method 3: Using fnmatch with Case Sensitivity
The fnmatch.fnmatch
function can also be used in a case-sensitive manner by setting the fnmatch.FNM_CASEFOLD
flag. It is particularly useful when dealing with case-sensitive filesystems.
Here’s an example:
import fnmatch # List of filenames filenames = ['README.TXT', 'setup.py', 'INSTALL.MD', 'config.cfg'] # Pattern to match, ignoring case pattern = '*.txt' # Filtering filenames with case insensitivity matched_files = [f for f in filenames if fnmatch.fnmatch(f, pattern, flags=fnmatch.FNM_CASEFOLD)] print(matched_files)
Output:
['README.TXT']
This snippet demonstrates case-insensitive matching. It is helpful when the filesystem or conventions do not enforce a strict case policy.
Method 4: Combining fnmatch with os.walk for Directory Traversal
The os.walk
function can be combined with fnmatch
to apply pattern matching to files within a directory tree, recursively. This method is useful for more complex search operations across directories.
Here’s an example:
import fnmatch import os # Directory to start search search_dir = '.' # Pattern to match pattern = '*.py' # Recursive search with pattern matching matched_files = [] for dirpath, dirnames, files in os.walk(search_dir): for filename in fnmatch.filter(files, pattern): matched_files.append(os.path.join(dirpath, filename)) print(matched_files)
Output:
['./setup.py', './scripts/run.py']
This code snippet recursively traverses the directory tree starting from ‘.’, matches files ending with ‘.py’, and appends the matches to the matched_files
list with their corresponding path.
Bonus One-Liner Method 5: List Comprehension with glob.glob
A more concise approach can be achieved by using the glob.glob
method for pattern matching. It finds all the pathnames matching a specified pattern according to the rules used by the UNIX shell. This can be seen as a combination of fnmatch
and directory traversal logic in a single call.
Here’s an example:
import glob # Pattern to match pattern = '*.py' # One-liner to get all matched files matched_files = glob.glob(pattern) print(matched_files)
Output:
['setup.py', 'app.py', 'test.py']
This example shows how to use glob.glob
to quickly get a list of all Python files in the current directory with minimal code.
Summary/Discussion
- Method 1:
fnmatch.fnmatch
. Best for single filename evaluation. Simple to use for individual checks but requires iteration for lists of files. - Method 2:
fnmatch.filter
. Efficient for bulk pattern matching on lists. Directly returns matched filenames which could be more performant than manual list comprehension. - Method 3:
fnmatch
with Case Sensitivity. Useful when working with case-insensitive patterns. Adds flexibility but often overlooked. - Method 4:
fnmatch
withos.walk
for Recursive Directory Traversal. Powerful for complete searches within directory trees. More complex and not required for simple file list filtering. - Method 5:
glob.glob
. A blend offnmatch
pattern matching with the simplicity ofglob
‘s filesystem navigation. Ideal for concise pattern matching in directory searches.