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annotate contrib/python-zstandard/zstandard/__init__.py @ 44493:02c47b74366c

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git: key off `git` in .hg/requires rather than separate file Differential Revision: https://phab.mercurial-scm.org/D8265
author Augie Fackler <raf@durin42.com>
date Tue, 10 Mar 2020 13:10:53 -0400
parents de7838053207
children 6000f5b25c9b
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1 # Copyright (c) 2017-present, Gregory Szorc
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2 # All rights reserved.
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3 #
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4 # This software may be modified and distributed under the terms
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5 # of the BSD license. See the LICENSE file for details.
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6
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7 """Python interface to the Zstandard (zstd) compression library."""
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8
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9 from __future__ import absolute_import, unicode_literals
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10
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11 # This module serves 2 roles:
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12 #
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13 # 1) Export the C or CFFI "backend" through a central module.
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14 # 2) Implement additional functionality built on top of C or CFFI backend.
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15
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16 import os
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17 import platform
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18
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19 # Some Python implementations don't support C extensions. That's why we have
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20 # a CFFI implementation in the first place. The code here import one of our
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21 # "backends" then re-exports the symbols from this module. For convenience,
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22 # we support falling back to the CFFI backend if the C extension can't be
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23 # imported. But for performance reasons, we only do this on unknown Python
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24 # implementation. Notably, for CPython we require the C extension by default.
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25 # Because someone will inevitably want special behavior, the behavior is
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26 # configurable via an environment variable. A potentially better way to handle
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27 # this is to import a special ``__importpolicy__`` module or something
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28 # defining a variable and `setup.py` could write the file with whatever
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29 # policy was specified at build time. Until someone needs it, we go with
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30 # the hacky but simple environment variable approach.
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31 _module_policy = os.environ.get("PYTHON_ZSTANDARD_IMPORT_POLICY", "default")
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32
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33 if _module_policy == "default":
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34 if platform.python_implementation() in ("CPython",):
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35 from zstd import *
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36
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37 backend = "cext"
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38 elif platform.python_implementation() in ("PyPy",):
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39 from .cffi import *
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40
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41 backend = "cffi"
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42 else:
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43 try:
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44 from zstd import *
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45
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46 backend = "cext"
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47 except ImportError:
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48 from .cffi import *
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49
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50 backend = "cffi"
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51 elif _module_policy == "cffi_fallback":
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52 try:
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53 from zstd import *
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54
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55 backend = "cext"
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56 except ImportError:
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57 from .cffi import *
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58
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59 backend = "cffi"
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60 elif _module_policy == "cext":
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61 from zstd import *
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62
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63 backend = "cext"
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64 elif _module_policy == "cffi":
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65 from .cffi import *
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66
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67 backend = "cffi"
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68 else:
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69 raise ImportError(
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70 "unknown module import policy: %s; use default, cffi_fallback, "
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71 "cext, or cffi" % _module_policy
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72 )
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73
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74 # Keep this in sync with python-zstandard.h.
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75 __version__ = "0.13.0"