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# Copyright (c) 2017-present, Gregory Szorc
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# All rights reserved.
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#
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# This software may be modified and distributed under the terms
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# of the BSD license. See the LICENSE file for details.
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"""Python interface to the Zstandard (zstd) compression library."""
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from __future__ import absolute_import, unicode_literals
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# This module serves 2 roles:
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#
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# 1) Export the C or CFFI "backend" through a central module.
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# 2) Implement additional functionality built on top of C or CFFI backend.
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import os
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import platform
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# Some Python implementations don't support C extensions. That's why we have
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# a CFFI implementation in the first place. The code here import one of our
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# "backends" then re-exports the symbols from this module. For convenience,
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# we support falling back to the CFFI backend if the C extension can't be
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# imported. But for performance reasons, we only do this on unknown Python
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# implementation. Notably, for CPython we require the C extension by default.
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# Because someone will inevitably want special behavior, the behavior is
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# configurable via an environment variable. A potentially better way to handle
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# this is to import a special ``__importpolicy__`` module or something
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# defining a variable and `setup.py` could write the file with whatever
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# policy was specified at build time. Until someone needs it, we go with
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# the hacky but simple environment variable approach.
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_module_policy = os.environ.get('PYTHON_ZSTANDARD_IMPORT_POLICY', 'default')
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if _module_policy == 'default':
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if platform.python_implementation() in ('CPython',):
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from zstd import *
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backend = 'cext'
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elif platform.python_implementation() in ('PyPy',):
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from zstd_cffi import *
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backend = 'cffi'
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else:
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try:
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from zstd import *
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backend = 'cext'
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except ImportError:
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from zstd_cffi import *
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backend = 'cffi'
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elif _module_policy == 'cffi_fallback':
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try:
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from zstd import *
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backend = 'cext'
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except ImportError:
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from zstd_cffi import *
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backend = 'cffi'
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elif _module_policy == 'cext':
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from zstd import *
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backend = 'cext'
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elif _module_policy == 'cffi':
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from zstd_cffi import *
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backend = 'cffi'
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else:
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raise ImportError('unknown module import policy: %s; use default, cffi_fallback, '
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'cext, or cffi' % _module_policy)
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