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function sanitize_filename

Maturity: 51

Sanitizes a filename string by replacing invalid filesystem characters with underscores and ensuring a valid output.

File:
/tf/active/vicechatdev/CDocs/utils/__init__.py
Lines:
87 - 104
Complexity:
simple

Purpose

This function ensures filenames are safe for use across different operating systems by removing or replacing characters that are invalid in Windows, Linux, or macOS filesystems. It handles edge cases like empty strings and whitespace, making it suitable for user-generated filenames, downloaded files, or dynamically created file paths. Common use cases include processing uploaded files, generating report filenames, or creating safe document names in content management systems.

Source Code

def sanitize_filename(filename: str) -> str:
    """
    Sanitize filename to remove invalid characters.
    
    Args:
        filename: Original filename
        
    Returns:
        Sanitized filename
    """
    # Replace characters that are invalid in filenames
    sanitized = re.sub(r'[\\/*?:"<>|]', "_", filename)
    # Remove leading/trailing whitespace
    sanitized = sanitized.strip()
    # Ensure we have a valid filename
    if not sanitized:
        sanitized = "document"
    return sanitized

Parameters

Name Type Default Kind
filename str - positional_or_keyword

Parameter Details

filename: The original filename string that needs to be sanitized. Can contain any characters including invalid filesystem characters like slashes, colons, asterisks, quotes, angle brackets, pipes, and backslashes. May also contain leading/trailing whitespace or be an empty string.

Return Value

Type: str

Returns a sanitized string safe for use as a filename. Invalid characters (\/*?:"<>|) are replaced with underscores. Leading and trailing whitespace is removed. If the resulting string is empty after sanitization, returns the default string 'document'. The return value is guaranteed to be a non-empty string suitable for filesystem operations.

Dependencies

  • re

Required Imports

import re

Usage Example

import re

def sanitize_filename(filename: str) -> str:
    sanitized = re.sub(r'[\\/*?:"<>|]', "_", filename)
    sanitized = sanitized.strip()
    if not sanitized:
        sanitized = "document"
    return sanitized

# Example usage
original = "my/file:name*.txt"
safe_name = sanitize_filename(original)
print(safe_name)  # Output: my_file_name_.txt

# Handle empty or whitespace-only strings
empty_result = sanitize_filename("   ")
print(empty_result)  # Output: document

# Handle special characters
special = "report<2024>|final?.pdf"
safe_special = sanitize_filename(special)
print(safe_special)  # Output: report_2024__final_.pdf

Best Practices

  • Always sanitize user-provided filenames before saving to filesystem to prevent path traversal attacks
  • Be aware that this function only handles character replacement and does not validate filename length limits (typically 255 characters on most systems)
  • Consider additional validation for reserved filenames on Windows (CON, PRN, AUX, NUL, COM1-9, LPT1-9)
  • The function preserves file extensions, but does not validate them - consider separate extension validation if needed
  • For internationalization, be aware that this function preserves Unicode characters which may not be supported on all filesystems
  • Consider combining with path validation to ensure the sanitized filename is used only as a basename, not a full path

Tags

filename sanitization validation filesystem string-processing file-handling security cross-platform utility text-cleaning

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