fnmatch

Module Overview

The fnmatch module allows you to match file names using wildcard patterns, similar to the wildcards you might use in a command shell like Bash.

Special Characters

Here's how the special characters work:

• ? - Matches any single character.

• * - Matches any sequence of characters, including empty.

• [] - Encloses a set of characters. Matches any character within the brackets.

• [!...] - Encloses a set of characters. Matches any character not within the brackets.

• . - By default, does not match a dot (period).

Real-World Example

Let's say you have a directory with files named:

file1.txt
file2.txt
file3.txt

You could use fnmatch to find all files ending with .txt:

import fnmatch

files = ['file1.txt', 'file2.txt', 'file3.txt']
result = fnmatch.filter(files, '*.txt')
print(result)  # Output: ['file1.txt', 'file2.txt', 'file3.txt']

Potential Applications

fnmatch is commonly used for:

• Filtering files based on file name patterns in directory listings.

• Autocompleting file names in text editors or command shells.

• Checking file names for specific formats or patterns (e.g., for validation).

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Glob-Style Wildcards

Glob-style wildcards are special characters used to match files and directories based on specific patterns. Here's a simplified explanation of each:

* (asterisk)

• Meaning: Matches everything.

• Example: "*.txt" matches all files ending in ".txt", regardless of their name.

? (question mark)

• Meaning: Matches any single character.

• Example: "col?r" matches "color", "colour", "co1or", etc.

[seq] (square brackets)

• Meaning: Matches any character within the specified sequence.

• Example: "f[aei]sh" matches "fish", "fesh", and "fash".

[!seq] (square brackets with exclamation)

• Meaning: Matches any character not within the specified sequence.

• Example: "[!aeiou]n" matches "kn", "gn", "wn", etc.

- (minus)

• Meaning: When used within square brackets, matches any character in the range specified before it.

• Example: "d[a-z-]" matches any single-letter lowercase directory name, including names with hyphens.

Real-World Applications

Glob-style wildcards are commonly used in:

• File Searching: To find files meeting specific criteria.

• Directory Creation: To create directories based on patterns.

• Data Filtering: To select specific data from lists or databases.

Code Implementation Examples

import fnmatch

# File Searching
files = fnmatch.filter(os.listdir('/tmp'), '*.log')

# Directory Creation
os.mkdir('/var/log/app', mode=0o755)
os.mkdir('/var/log/web', mode=0o755)

# Data Filtering
data = ['apple', 'banana', 'cherry', 'dog', 'fish', 'grape']
fruits = fnmatch.filter(data, '*[aeiou]*')
print(fruits)  # ['apple', 'banana', 'cherry', 'grape']

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Literal Meta-characters

• Meaning: These characters match themselves exactly.

• Syntax: Wrap them in brackets.

• Example: '?' matches the character '?'.

Non-Special Filename Separator

• Meaning: The filename separator (e.g., / in Unix) is not special in fnmatch.

• Implication: Pass the entire filename path to fnmatch, and it will apply the patterns to individual filename segments.

Matching Hidden Files

• Meaning: Filenames starting with a period (e.g., .hidden) are not treated specially.

• Note: They will match patterns like '*' and '?'.

Cached Compiled Regex Patterns

• Meaning: The fnmatch, fnmatchcase, and filter functions use a cache to store compiled regex patterns.

• Benefit: It improves performance by preventing duplicate compilation of the same patterns.

Real-World Applications

• File Filtering: Filtering files based on matching patterns.

• Path Manipulation: Matching specific path segments in complex file paths.

• Config File Parsing: Identifying configuration parameters based on matching patterns.

Improved Code Example

import fnmatch

# Filter files with the pattern '*.py'
for file in os.listdir("./"):
    if fnmatch.fnmatch(file, "*.py"):
        print(file)

# Check if a file 'config.json' matches the pattern 'config*'
fnmatch.fnmatch("config.json", "config*")

# Filter files that start with 'hidden'
for file in os.listdir("./"):
    if fnmatch.fnmatch(file, "hidden*"):
        print(file)

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1. Understanding fnmatch()

Simplified Explanation:

fnmatch() is a function that checks if a file name matches a specific pattern. It's like a secret code that you can use to find files that follow a certain rule.

For example:

If you want to find all files that end with the extension ".txt", you can use the pattern "*.txt".

2. Using fnmatch()

Code Snippet:

import fnmatch

# Get a list of files in the current directory
files = os.listdir('.')

# Find all files that match the "*.txt" pattern
txt_files = []
for file in files:
    if fnmatch.fnmatch(file, "*.txt"):
        txt_files.append(file)

# Print the list of ".txt" files
print(txt_files)

Explanation:

This code first lists all files in the current directory. Then, it iterates through each file and checks if it matches the "*.txt" pattern. If a file matches, it's added to the "txt_files" list. Finally, the "txt_files" list is printed.

Real-World Applications:

• Searching for specific file types in a large directory

• Filtering files based on patterns in file management systems

• Automating tasks that involve finding files that meet certain criteria

3. fnmatchcase()

Simplified Explanation:

fnmatch() normally ignores the case of file names when matching patterns. For example, "text.txt" and "TEXT.TXT" would both match the "*.txt" pattern.

fnmatchcase() is a special version of fnmatch() that considers the case of file names. If you use fnmatchcase() with the "*.txt" pattern, only files with the exact name "text.txt" would match.

Code Snippet:

import fnmatch

# Get a list of files in the current directory
files = os.listdir('.')

# Find all files that match the "*.txt" pattern, case-sensitively
txt_files = []
for file in files:
    if fnmatchcase(file, "*.txt"):
        txt_files.append(file)

# Print the list of ".txt" files
print(txt_files)

Real-World Applications:

• Finding files with specific case-sensitive names

• Ensuring that files are named consistently and accurately

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fnmatchcase Function in fnmatch Module

The fnmatchcase function in Python's fnmatch module performs case-sensitive pattern matching on filenames. It returns True if the given name matches the pat pattern, and False otherwise.

Parameters:

• name: A string representing the filename to be matched.

• pat: A string representing the pattern to be matched against. The pattern can contain wildcards like * (matches any number of characters) and ? (matches a single character).

Return Value:

• bool: Returns True if the name matches the pat pattern, False otherwise.

Example:

import fnmatch

name = 'myfile.txt'
pat = '*.txt'

result = fnmatchcase(name, pat)
print(result)  # Output: True

Real-World Applications:

• Filtering files based on their names. For example, you could use fnmatchcase to find all files with a specific extension or name.

• Matching filenames against user-defined patterns. For instance, you could use fnmatchcase to check if a file matches a set of criteria defined by the user.

Improved Code Snippet:

import fnmatch

def find_files(directory, pattern):
    """
    Finds all files in the given directory that match the specified pattern.

    Args:
        directory: The directory to search.
        pattern: The pattern to match against.

    Returns:
        A list of matching files.
    """

    # Iterate over all files in the directory.
    for filename in os.listdir(directory):

        # Check if the filename matches the pattern.
        if fnmatchcase(filename, pattern):

            # If it does, add it to the list of matching files.
            matching_files.append(filename)

    # Return the list of matching files.
    return matching_files

This code snippet shows how to use fnmatchcase to find all files in a given directory that match a specific pattern.

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Simplified Explanation:

The fnmatch.filter() function takes two inputs: a list of names and a pattern. It returns a new list containing only the names that match the pattern.

Detailed Explanation:

Input Parameters:

• names: A list of strings (file names or other names).

• pat: A pattern (a string containing wildcards) to match the names against.

Matching Patterns:

The pattern pat can contain the following wildcard characters:

• *: Matches any number of characters.

• ?: Matches any single character.

• [...]: Matches any character within the square brackets.

Implementation:

The fnmatch.filter() function is implemented more efficiently than the following Python list comprehension:

[n for n in names if fnmatch(n, pat)]

Real-World Application:

The fnmatch.filter() function can be used in various real-world scenarios:

• File searching: To search for files with specific names or patterns, such as finding all ".txt" files in a directory.

• Data filtering: To extract data from a list or array that matches certain criteria, such as filtering a list of email addresses to only include those from a specific domain.

• Text processing: To identify and manipulate text that conforms to a particular pattern, such as extracting phone numbers or URLs from a document.

Improved Code Examples:

Here's a complete code implementation of how to use fnmatch.filter() to find all ".txt" files in a directory:

import fnmatch
import os

# Get the current working directory
cwd = os.getcwd()

# Create a list of all files in the directory
files = os.listdir(cwd)

# Use fnmatch.filter() to find all ".txt" files
txt_files = fnmatch.filter(files, "*.txt")

# Print the list of ".txt" files
print(txt_files)

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Function translate(pat)

Purpose:

Converts a shell-style file pattern (pat) into a regular expression that can be used with the re.match function for pattern matching.

How it works:

Imagine you have a file pattern like *.txt. This pattern means "match any file that ends with .txt." However, to use this pattern in a Python program, we need to convert it into a regular expression. The translate function does this conversion for us.

Example:

import fnmatch
import re

# Convert the file pattern "*.txt" into a regular expression
regex = fnmatch.translate("*.txt")

# Compile the regular expression into a match object
regex_object = re.compile(regex)

# Use the match object to match against a file name
match = regex_object.match("foobar.txt")

# Check if the match was successful
if match:
    print("Matched the file name")

Improved Example:

import fnmatch
import re

# Define a function to check if a file name matches a pattern
def check_file_match(file_name, pattern):
    # Convert the pattern to a regular expression
    regex = fnmatch.translate(pattern)

    # Create a match object
    regex_object = re.compile(regex)

    # Match the file name against the pattern
    match = regex_object.match(file_name)

    # Return the result of the match
    return bool(match)

# Test the function with different file names and patterns
print(check_file_match("foobar.txt", "*.txt"))  # True
print(check_file_match("foobar.cpp", "*.txt"))  # False

Potential Applications:

• File searching: Find files with specific names or extensions within a directory.

• Filename validation: Check if a user-provided file name matches a specific format.

• Pattern matching: Identify text strings that match a predefined set of characters.