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Differential Revision: https://phab.mercurial-scm.org/D153
author | Siddharth Agarwal <sid0@fb.com> |
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date | Thu, 20 Jul 2017 18:04:21 -0700 |
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1 # demandimportpy3 - global demand-loading of modules for Mercurial |
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2 # |
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3 # Copyright 2017 Facebook Inc. |
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4 # |
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5 # This software may be used and distributed according to the terms of the |
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6 # GNU General Public License version 2 or any later version. |
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7 |
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8 """Lazy loading for Python 3.6 and above. |
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9 |
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10 This uses the new importlib finder/loader functionality available in Python 3.5 |
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11 and up. The code reuses most of the mechanics implemented inside importlib.util, |
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12 but with a few additions: |
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13 |
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14 * Allow excluding certain modules from lazy imports. |
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15 * Expose an interface that's substantially the same as demandimport for |
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16 Python 2. |
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17 |
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18 This also has some limitations compared to the Python 2 implementation: |
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19 |
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20 * Much of the logic is per-package, not per-module, so any packages loaded |
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21 before demandimport is enabled will not be lazily imported in the future. In |
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22 practice, we only expect builtins to be loaded before demandimport is |
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23 enabled. |
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24 """ |
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25 |
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26 # This line is unnecessary, but it satisfies test-check-py3-compat.t. |
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27 from __future__ import absolute_import |
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28 |
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29 import contextlib |
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30 import os |
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31 import sys |
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32 |
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33 import importlib.abc |
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34 import importlib.machinery |
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35 import importlib.util |
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36 |
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37 _deactivated = False |
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38 |
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39 class _lazyloaderex(importlib.util.LazyLoader): |
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40 """This is a LazyLoader except it also follows the _deactivated global and |
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41 the ignore list. |
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42 """ |
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43 def exec_module(self, module): |
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44 """Make the module load lazily.""" |
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45 if _deactivated or module.__name__ in ignore: |
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46 self.loader.exec_module(module) |
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47 else: |
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48 super().exec_module(module) |
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49 |
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50 # This is 3.6+ because with Python 3.5 it isn't possible to lazily load |
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51 # extensions. See the discussion in https://python.org/sf/26186 for more. |
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52 _extensions_loader = _lazyloaderex.factory( |
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53 importlib.machinery.ExtensionFileLoader) |
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54 _bytecode_loader = _lazyloaderex.factory( |
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55 importlib.machinery.SourcelessFileLoader) |
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56 _source_loader = _lazyloaderex.factory(importlib.machinery.SourceFileLoader) |
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57 |
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58 def _makefinder(path): |
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59 return importlib.machinery.FileFinder( |
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60 path, |
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61 # This is the order in which loaders are passed in in core Python. |
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62 (_extensions_loader, importlib.machinery.EXTENSION_SUFFIXES), |
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63 (_source_loader, importlib.machinery.SOURCE_SUFFIXES), |
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64 (_bytecode_loader, importlib.machinery.BYTECODE_SUFFIXES), |
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65 ) |
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66 |
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67 ignore = [] |
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68 |
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69 def init(ignorelist): |
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70 global ignore |
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71 ignore = ignorelist |
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72 |
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73 def isenabled(): |
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74 return _makefinder in sys.path_hooks and not _deactivated |
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75 |
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76 def disable(): |
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77 try: |
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78 while True: |
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79 sys.path_hooks.remove(_makefinder) |
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80 except ValueError: |
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81 pass |
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82 |
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83 def enable(): |
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84 if os.environ.get('HGDEMANDIMPORT') != 'disable': |
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85 sys.path_hooks.insert(0, _makefinder) |
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86 |
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87 @contextlib.contextmanager |
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88 def deactivated(): |
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89 # This implementation is a bit different from Python 2's. Python 3 |
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90 # maintains a per-package finder cache in sys.path_importer_cache (see |
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91 # PEP 302). This means that we can't just call disable + enable. |
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92 # If we do that, in situations like: |
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93 # |
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94 # demandimport.enable() |
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95 # ... |
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96 # from foo.bar import mod1 |
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97 # with demandimport.deactivated(): |
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98 # from foo.bar import mod2 |
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99 # |
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100 # mod2 will be imported lazily. (The converse also holds -- whatever finder |
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101 # first gets cached will be used.) |
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102 # |
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103 # Instead, have a global flag the LazyLoader can use. |
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104 global _deactivated |
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105 demandenabled = isenabled() |
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106 if demandenabled: |
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107 _deactivated = True |
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108 try: |
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109 yield |
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110 finally: |
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111 if demandenabled: |
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112 _deactivated = False |