# 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`: ```python 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). *** ### 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 ```python 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'] ``` *** **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** ```python 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) ``` *** **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:** ```python 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:** ```python 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 *** ### `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:** ```python 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:** ```python 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. *** **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: ```python [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: ```python 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) ``` *** **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:** ```python 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:** ```python 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.