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annotate hgdemandimport/demandimportpy3.py @ 49536:87516dd774d0

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demandimport: remove an obsolete comment about importing from future See 6000f5b25c9b.
author Anton Shestakov <av6@dwimlabs.net>
date Mon, 31 Oct 2022 16:36:00 +0400
parents b8eb29ab3906
children 7236f11db0c3
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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 import contextlib
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27 import importlib.util
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28 import sys
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29
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30 from . import tracing
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31
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32 _deactivated = False
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33
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34
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35 class _lazyloaderex(importlib.util.LazyLoader):
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36 """This is a LazyLoader except it also follows the _deactivated global and
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37 the ignore list.
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38 """
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39
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40 def exec_module(self, module):
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41 """Make the module load lazily."""
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42 with tracing.log('demandimport %s', module):
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43 if _deactivated or module.__name__ in ignores:
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44 self.loader.exec_module(module)
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45 else:
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46 super().exec_module(module)
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47
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48
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49 class LazyFinder:
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50 """A wrapper around a ``MetaPathFinder`` that makes loaders lazy.
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51
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52 ``sys.meta_path`` finders have their ``find_spec()`` called to locate a
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53 module. This returns a ``ModuleSpec`` if found or ``None``. The
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54 ``ModuleSpec`` has a ``loader`` attribute, which is called to actually
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55 load a module.
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56
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57 Our class wraps an existing finder and overloads its ``find_spec()`` to
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58 replace the ``loader`` with our lazy loader proxy.
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59
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60 We have to use __getattribute__ to proxy the instance because some meta
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61 path finders don't support monkeypatching.
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62 """
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63
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64 __slots__ = ("_finder",)
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65
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66 def __init__(self, finder):
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67 object.__setattr__(self, "_finder", finder)
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68
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69 def __repr__(self):
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70 return "<LazyFinder for %r>" % object.__getattribute__(self, "_finder")
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71
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72 # __bool__ is canonical Python 3. But check-code insists on __nonzero__ being
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73 # defined via `def`.
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74 def __nonzero__(self):
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75 return bool(object.__getattribute__(self, "_finder"))
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76
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77 __bool__ = __nonzero__
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78
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79 def __getattribute__(self, name):
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80 if name in ("_finder", "find_spec"):
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81 return object.__getattribute__(self, name)
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82
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83 return getattr(object.__getattribute__(self, "_finder"), name)
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84
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85 def __delattr__(self, name):
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86 return delattr(object.__getattribute__(self, "_finder"))
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87
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88 def __setattr__(self, name, value):
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89 return setattr(object.__getattribute__(self, "_finder"), name, value)
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90
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91 def find_spec(self, fullname, path, target=None):
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92 finder = object.__getattribute__(self, "_finder")
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93 try:
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94 find_spec = finder.find_spec
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95 except AttributeError:
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96 loader = finder.find_module(fullname, path)
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97 if loader is None:
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98 spec = None
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99 else:
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100 spec = importlib.util.spec_from_loader(fullname, loader)
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101 else:
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102 spec = find_spec(fullname, path, target)
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103
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104 # Lazy loader requires exec_module().
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105 if (
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106 spec is not None
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107 and spec.loader is not None
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108 and getattr(spec.loader, "exec_module", None)
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109 ):
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110 spec.loader = _lazyloaderex(spec.loader)
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111
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112 return spec
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113
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114
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115 ignores = set()
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116
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117
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118 def init(ignoreset):
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119 global ignores
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120 ignores = ignoreset
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121
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122
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123 def isenabled():
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124 return not _deactivated and any(
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125 isinstance(finder, LazyFinder) for finder in sys.meta_path
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126 )
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127
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128
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129 def disable():
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130 new_finders = []
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131 for finder in sys.meta_path:
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132 new_finders.append(
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133 finder._finder if isinstance(finder, LazyFinder) else finder
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134 )
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135 sys.meta_path[:] = new_finders
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136
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137
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138 def enable():
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139 new_finders = []
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140 for finder in sys.meta_path:
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141 new_finders.append(
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142 LazyFinder(finder) if not isinstance(finder, LazyFinder) else finder
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143 )
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144 sys.meta_path[:] = new_finders
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145
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146
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147 @contextlib.contextmanager
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148 def deactivated():
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149 # This implementation is a bit different from Python 2's. Python 3
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150 # maintains a per-package finder cache in sys.path_importer_cache (see
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151 # PEP 302). This means that we can't just call disable + enable.
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152 # If we do that, in situations like:
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153 #
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154 # demandimport.enable()
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155 # ...
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156 # from foo.bar import mod1
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157 # with demandimport.deactivated():
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158 # from foo.bar import mod2
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159 #
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160 # mod2 will be imported lazily. (The converse also holds -- whatever finder
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161 # first gets cached will be used.)
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162 #
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163 # Instead, have a global flag the LazyLoader can use.
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164 global _deactivated
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165 demandenabled = isenabled()
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166 if demandenabled:
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167 _deactivated = True
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168 try:
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169 yield
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170 finally:
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171 if demandenabled:
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172 _deactivated = False