Lib/fnmatch.py

Source:

cpython 3.14 @ ab2d84fe1023/Lib/fnmatch.py ↗

fnmatch matches filenames against Unix shell-style glob patterns. It is used by pathlib, glob, shutil, and tarfile.

Map

Lines	Symbol	Role
1-30	fnmatch	Case-insensitive on Windows, case-sensitive on POSIX
31-60	fnmatchcase	Always case-sensitive
61-100	translate	Convert glob pattern to a regex string
101-130	filter	[name for name in names if fnmatch(name, pat)]

Reading

fnmatch

# CPython: Lib/fnmatch.py:28 fnmatch
def fnmatch(name, pat):
    """Test whether NAME matches PAT.
    Pattern language:
      *      — matches everything (not path separators in most contexts)
      ?      — matches any single character
      [seq]  — matches any character in seq
      [!seq] — matches any character not in seq
    """
    name = os.path.normcase(name)
    pat  = os.path.normcase(pat)
    return fnmatchcase(name, pat)

os.path.normcase lowercases on Windows; is a no-op on POSIX.

translate

# CPython: Lib/fnmatch.py:65 translate
def translate(pat):
    """Translate a shell PATTERN to a regular expression.
    There is no way to quote meta-characters.
    """
    i, n = 0, len(pat)
    res = ''
    while i < n:
        c = pat[i]
        i += 1
        if c == '*':
            res += '.*'
        elif c == '?':
            res += '.'
        elif c == '[':
            # Character class — find matching ']'
            j = i
            if j < n and pat[j] == '!': j += 1
            if j < n and pat[j] == ']': j += 1
            while j < n and pat[j] != ']': j += 1
            if j >= n:
                res += r'\['
            else:
                stuff = pat[i:j].replace('\\', '\\\\')
                i = j + 1
                if stuff[0] == '!':
                    stuff = '^' + stuff[1:]
                elif stuff[0] == '^':
                    stuff = '\\' + stuff
                res += '[' + stuff + ']'
        else:
            res += re.escape(c)
    return r'(?s:%s)\Z' % res

fnmatch.translate('*.py') → '(?s:.*\\.py)\\Z'. The (?s:...) flag makes . match newlines.

filter

# CPython: Lib/fnmatch.py:115 filter
def filter(names, pat):
    """Construct a list of all names matching pat."""
    result = []
    pat = os.path.normcase(pat)
    match = _compile_pattern(pat)
    if os.path is posixpath:
        for name in names:
            if match(name):
                result.append(name)
    else:
        for name in names:
            if match(os.path.normcase(name)):
                result.append(name)
    return result

_compile_pattern caches compiled regexes using functools.lru_cache.

gopy notes

fnmatch is pure Python and importable when re, os, and functools work. The translate function's regex output is used directly by pathlib.Path.glob() via fnmatch.translate. The LRU cache for compiled patterns avoids re-compilation on repeated use with the same pattern.