author | Anton Shestakov <av6@dwimlabs.net> |
Sun, 02 Sep 2018 08:40:57 +0800 | |
changeset 39399 | c54d4607e8aa |
parent 37495 | b1fb341d8a61 |
child 40121 | 73fef626dae3 |
permissions | -rw-r--r-- |
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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) |