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annotate hgdemandimport/demandimportpy3.py @ 48946:642e31cb55f0

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py3: use class X: instead of class X(object): The inheritance from object is implied in Python 3. So this should be equivalent. This change was generated via an automated search and replace. So there may have been some accidental changes. Differential Revision: https://phab.mercurial-scm.org/D12352
author Gregory Szorc <gregory.szorc@gmail.com>
date Mon, 21 Feb 2022 13:08:28 -0700
parents 6000f5b25c9b
children b8eb29ab3906
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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
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28 import contextlib
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29 import importlib.util
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30 import sys
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31
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32 from . import tracing
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33
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34 _deactivated = False
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35
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36 # Python 3.5's LazyLoader doesn't work for some reason.
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37 # https://bugs.python.org/issue26186 is a known issue with extension
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38 # importing. But it appears to not have a meaningful effect with
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39 # Mercurial.
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40 _supported = sys.version_info[0:2] >= (3, 6)
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41
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42
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43 class _lazyloaderex(importlib.util.LazyLoader):
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44 """This is a LazyLoader except it also follows the _deactivated global and
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45 the ignore list.
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46 """
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47
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48 def exec_module(self, module):
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49 """Make the module load lazily."""
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50 with tracing.log('demandimport %s', module):
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51 if _deactivated or module.__name__ in ignores:
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52 self.loader.exec_module(module)
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53 else:
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54 super().exec_module(module)
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56
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57 class LazyFinder:
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58 """A wrapper around a ``MetaPathFinder`` that makes loaders lazy.
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59
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60 ``sys.meta_path`` finders have their ``find_spec()`` called to locate a
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61 module. This returns a ``ModuleSpec`` if found or ``None``. The
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62 ``ModuleSpec`` has a ``loader`` attribute, which is called to actually
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63 load a module.
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64
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65 Our class wraps an existing finder and overloads its ``find_spec()`` to
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66 replace the ``loader`` with our lazy loader proxy.
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67
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68 We have to use __getattribute__ to proxy the instance because some meta
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69 path finders don't support monkeypatching.
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70 """
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71
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72 __slots__ = ("_finder",)
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73
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74 def __init__(self, finder):
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75 object.__setattr__(self, "_finder", finder)
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76
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77 def __repr__(self):
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78 return "<LazyFinder for %r>" % object.__getattribute__(self, "_finder")
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79
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80 # __bool__ is canonical Python 3. But check-code insists on __nonzero__ being
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81 # defined via `def`.
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82 def __nonzero__(self):
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83 return bool(object.__getattribute__(self, "_finder"))
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84
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85 __bool__ = __nonzero__
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86
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87 def __getattribute__(self, name):
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88 if name in ("_finder", "find_spec"):
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89 return object.__getattribute__(self, name)
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90
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91 return getattr(object.__getattribute__(self, "_finder"), name)
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92
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93 def __delattr__(self, name):
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94 return delattr(object.__getattribute__(self, "_finder"))
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95
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96 def __setattr__(self, name, value):
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97 return setattr(object.__getattribute__(self, "_finder"), name, value)
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98
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99 def find_spec(self, fullname, path, target=None):
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100 finder = object.__getattribute__(self, "_finder")
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101 try:
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102 find_spec = finder.find_spec
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103 except AttributeError:
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104 loader = finder.find_module(fullname, path)
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105 if loader is None:
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106 spec = None
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107 else:
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108 spec = importlib.util.spec_from_loader(fullname, loader)
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109 else:
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110 spec = find_spec(fullname, path, target)
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111
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112 # Lazy loader requires exec_module().
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113 if (
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114 spec is not None
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115 and spec.loader is not None
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116 and getattr(spec.loader, "exec_module", None)
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117 ):
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118 spec.loader = _lazyloaderex(spec.loader)
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119
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120 return spec
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121
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122
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123 ignores = set()
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124
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125
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126 def init(ignoreset):
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127 global ignores
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128 ignores = ignoreset
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129
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130
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131 def isenabled():
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132 return not _deactivated and any(
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133 isinstance(finder, LazyFinder) for finder in sys.meta_path
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134 )
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135
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136
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137 def disable():
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138 new_finders = []
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139 for finder in sys.meta_path:
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140 new_finders.append(
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141 finder._finder if isinstance(finder, LazyFinder) else finder
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142 )
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143 sys.meta_path[:] = new_finders
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144
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145
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146 def enable():
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147 if not _supported:
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148 return
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149
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150 new_finders = []
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151 for finder in sys.meta_path:
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152 new_finders.append(
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153 LazyFinder(finder) if not isinstance(finder, LazyFinder) else finder
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154 )
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155 sys.meta_path[:] = new_finders
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156
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157
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158 @contextlib.contextmanager
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159 def deactivated():
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160 # This implementation is a bit different from Python 2's. Python 3
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161 # maintains a per-package finder cache in sys.path_importer_cache (see
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162 # PEP 302). This means that we can't just call disable + enable.
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163 # If we do that, in situations like:
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164 #
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165 # demandimport.enable()
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166 # ...
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167 # from foo.bar import mod1
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168 # with demandimport.deactivated():
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169 # from foo.bar import mod2
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170 #
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171 # mod2 will be imported lazily. (The converse also holds -- whatever finder
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172 # first gets cached will be used.)
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173 #
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174 # Instead, have a global flag the LazyLoader can use.
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175 global _deactivated
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176 demandenabled = isenabled()
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177 if demandenabled:
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178 _deactivated = True
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179 try:
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180 yield
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181 finally:
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182 if demandenabled:
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183 _deactivated = False