contrib/python-zstandard/zstandard/__init__.py

dirstate: add a `set_tracked` method for "hg add"-like usage

This is a step further toward clarifying the semantic of various dirstate call.

Having a dedicated function comes with a couple of benefits:

1) we can move duplicated logic about how to handle the previous state within
the dirstate. Since we are sure this is always called in the same situation, we
can implement that logic once in the dirstate.

2) having a dedicated method for this case unlock also having a dedicated
method for the other case and recording more information at that time. All this
leading having more code within the dirstate and higher level API that are less
error prone.

Differential Revision: https://phab.mercurial-scm.org/D11013

# Copyright (c) 2017-present, Gregory Szorc
# All rights reserved.
#
# This software may be modified and distributed under the terms
# of the BSD license. See the LICENSE file for details.

"""Python interface to the Zstandard (zstd) compression library."""

from __future__ import absolute_import, unicode_literals

# This module serves 2 roles:
#
# 1) Export the C or CFFI "backend" through a central module.
# 2) Implement additional functionality built on top of C or CFFI backend.

import os
import platform

# Some Python implementations don't support C extensions. That's why we have
# a CFFI implementation in the first place. The code here import one of our
# "backends" then re-exports the symbols from this module. For convenience,
# we support falling back to the CFFI backend if the C extension can't be
# imported. But for performance reasons, we only do this on unknown Python
# implementation. Notably, for CPython we require the C extension by default.
# Because someone will inevitably want special behavior, the behavior is
# configurable via an environment variable. A potentially better way to handle
# this is to import a special ``__importpolicy__`` module or something
# defining a variable and `setup.py` could write the file with whatever
# policy was specified at build time. Until someone needs it, we go with
# the hacky but simple environment variable approach.
_module_policy = os.environ.get("PYTHON_ZSTANDARD_IMPORT_POLICY", "default")

if _module_policy == "default":
    if platform.python_implementation() in ("CPython",):
        from zstd import *

        backend = "cext"
    elif platform.python_implementation() in ("PyPy",):
        from .cffi import *

        backend = "cffi"
    else:
        try:
            from zstd import *

            backend = "cext"
        except ImportError:
            from .cffi import *

            backend = "cffi"
elif _module_policy == "cffi_fallback":
    try:
        from zstd import *

        backend = "cext"
    except ImportError:
        from .cffi import *

        backend = "cffi"
elif _module_policy == "cext":
    from zstd import *

    backend = "cext"
elif _module_policy == "cffi":
    from .cffi import *

    backend = "cffi"
else:
    raise ImportError(
        "unknown module import policy: %s; use default, cffi_fallback, "
        "cext, or cffi" % _module_policy
    )

# Keep this in sync with python-zstandard.h.
__version__ = "0.13.0"