Lib/tempfile.py

Source:

cpython 3.14 @ ab2d84fe1023/Lib/tempfile.py ↗

tempfile creates temporary files and directories that are automatically removed when closed or when a context manager exits.

Map

Lines	Symbol	Role
1-80	_get_candidate_names	Generate random suffixes for temp names
81-200	mkstemp, mkdtemp	Low-level: create and return (fd, path) or path
201-350	TemporaryFile	Anonymous file (unlinked immediately on POSIX)
351-500	NamedTemporaryFile	Visible file with delete=True by default
501-620	SpooledTemporaryFile	In-memory until max_size bytes, then spills to disk
621-800	TemporaryDirectory	Directory removed on __exit__ or cleanup()

Reading

Secure name generation

# CPython: Lib/tempfile.py:75 _get_candidate_names
class _RandomNameSequence:
    """An instance of _RandomNameSequence generates an endless
    sequence of unpredictable strings which can safely be incorporated
    into file names.  Each string is eight characters long."""
    characters = "abcdefghijklmnopqrstuvwxyz0123456789_"
    @property
    def rng(self):
        cur_pid = os.getpid()
        if cur_pid != getattr(self, '_rng_pid', None):
            self._rng = Random()
            self._rng_pid = cur_pid
        return self._rng
    def __iter__(self):
        c = self.characters
        choose = self.rng.choice
        letters = [choose(c) for _ in range(8)]
        yield ''.join(letters)

A fresh Random() is seeded from OS entropy. The PID check ensures correctness after os.fork().

mkstemp

# CPython: Lib/tempfile.py:155 mkstemp
def mkstemp(suffix=None, prefix=None, dir=None, text=False):
    """Create and return a unique temporary file.
    The return value is a pair (fd, name).
    fd — an OS-level file descriptor (int), suitable for os.fdopen()
    name — the absolute path
    The file is not deleted automatically.
    """
    prefix, suffix, dir, output_type = _sanitize_params(prefix, suffix, dir)
    file, name = _mkstemp_inner(dir, prefix, suffix, flags, output_type)
    return file, name

mkstemp is the low-level function; callers are responsible for deletion. NamedTemporaryFile wraps it with auto-delete.

TemporaryFile

# CPython: Lib/tempfile.py:240 TemporaryFile
def TemporaryFile(mode='w+b', buffering=-1, encoding=None,
                  newline=None, suffix=None, prefix=None, dir=None, *,
                  errors=None):
    """On POSIX, the file is created and immediately unlinked so it has
    no directory entry and is invisible to other processes."""
    (fd, name) = _mkstemp_inner(dir, prefix, suffix, flags, output_type)
    try:
        os.unlink(name)   # POSIX: remove directory entry immediately
        return io.open(fd, mode, buffering, encoding, newline, errors=errors)
    except:
        os.close(fd)
        raise

On POSIX, unlink after open means the file exists until the last fd is closed. On Windows, a DELETE_ON_CLOSE flag achieves the same effect.

SpooledTemporaryFile

# CPython: Lib/tempfile.py:530 SpooledTemporaryFile
class SpooledTemporaryFile:
    """A file-like object that starts as an in-memory BytesIO/StringIO
    and spills to a real TemporaryFile once it exceeds max_size bytes."""
    def write(self, s):
        if self._rolled:
            return self._file.write(s)
        buf = self._file
        rv = buf.write(s)
        if self._max_size and buf.tell() > self._max_size:
            self.rollover()  # spill to disk
        return rv

TemporaryDirectory

# CPython: Lib/tempfile.py:680 TemporaryDirectory
class TemporaryDirectory:
    def __init__(self, suffix=None, prefix=None, dir=None,
                 ignore_cleanup_errors=False, *, delete=True):
        self.name = mkdtemp(suffix, prefix, dir)
        self._delete = delete

    def cleanup(self):
        if self._delete and os.path.exists(self.name):
            shutil.rmtree(self.name)

    def __exit__(self, exc, value, tb):
        self.cleanup()

gopy notes

tempfile is pure Python and importable in gopy when os, io, shutil, and random work. mkstemp calls os.open with O_CREAT|O_EXCL. TemporaryFile relies on os.unlink while the fd is still open — POSIX semantics that gopy passes through to the OS via syscall.Unlink.