Lib/__future__.py

   1 """Record of phased-in incompatible language changes.
   2
   3 Each line is of the form:
   4
   5     FeatureName = "_Feature(" OptionalRelease "," MandatoryRelease ","
   6                               CompilerFlag ")"
   7
   8 where, normally, OptionalRelease < MandatoryRelease, and both are 5-tuples
   9 of the same form as sys.version_info:
  10
  11     (PY_MAJOR_VERSION, # the 2 in 2.1.0a3; an int
  12      PY_MINOR_VERSION, # the 1; an int
  13      PY_MICRO_VERSION, # the 0; an int
  14      PY_RELEASE_LEVEL, # "alpha", "beta", "candidate" or "final"; string
  15      PY_RELEASE_SERIAL # the 3; an int
  16     )
  17
  18 OptionalRelease records the first release in which
  19
  20     from __future__ import FeatureName
  21
  22 was accepted.
  23
  24 In the case of MandatoryReleases that have not yet occurred,
  25 MandatoryRelease predicts the release in which the feature will become part
  26 of the language.
  27
  28 Else MandatoryRelease records when the feature became part of the language;
  29 in releases at or after that, modules no longer need
  30
  31     from __future__ import FeatureName
  32
  33 to use the feature in question, but may continue to use such imports.
  34
  35 MandatoryRelease may also be None, meaning that a planned feature got
  36 dropped.
  37
  38 Instances of class _Feature have two corresponding methods,
  39 .getOptionalRelease() and .getMandatoryRelease().
  40
  41 CompilerFlag is the (bitfield) flag that should be passed in the fourth
  42 argument to the builtin function compile() to enable the feature in
  43 dynamically compiled code.  This flag is stored in the .compiler_flag
  44 attribute on _Future instances.  These values must match the appropriate
  45 #defines of CO_xxx flags in Include/compile.h.
  46
  47 No feature line is ever to be deleted from this file.
  48 """
  49
  50 all_feature_names = [
  51     "nested_scopes",
  52     "generators",
  53     "division",
  54     "absolute_import",
  55     "with_statement",
  56 ]
  57
  58 __all__ = ["all_feature_names"] + all_feature_names
  59
  60 # The CO_xxx symbols are defined here under the same names used by
  61 # compile.h, so that an editor search will find them here.  However,
  62 # they're not exported in __all__, because they don't really belong to
  63 # this module.
  64 CO_NESTED            = 0x0010   # nested_scopes
  65 CO_GENERATOR_ALLOWED = 0        # generators (obsolete, was 0x1000)
  66 CO_FUTURE_DIVISION   = 0x2000   # division
  67 CO_FUTURE_ABSOLUTE_IMPORT = 0x4000 # perform absolute imports by default
  68 CO_FUTURE_WITH_STATEMENT  = 0x8000   # with statement
  69
  70 class _Feature:
  71     def __init__(self, optionalRelease, mandatoryRelease, compiler_flag):
  72         self.optional = optionalRelease
  73         self.mandatory = mandatoryRelease
  74         self.compiler_flag = compiler_flag
  75
  76     def getOptionalRelease(self):
  77         """Return first release in which this feature was recognized.
  78
  79         This is a 5-tuple, of the same form as sys.version_info.
  80         """
  81
  82         return self.optional
  83
  84     def getMandatoryRelease(self):
  85         """Return release in which this feature will become mandatory.
  86
  87         This is a 5-tuple, of the same form as sys.version_info, or, if
  88         the feature was dropped, is None.
  89         """
  90
  91         return self.mandatory
  92
  93     def __repr__(self):
  94         return "_Feature" + repr((self.optional,
  95                                   self.mandatory,
  96                                   self.compiler_flag))
  97
  98 nested_scopes = _Feature((2, 1, 0, "beta",  1),
  99                          (2, 2, 0, "alpha", 0),
 100                          CO_NESTED)
 101
 102 generators = _Feature((2, 2, 0, "alpha", 1),
 103                       (2, 3, 0, "final", 0),
 104                       CO_GENERATOR_ALLOWED)
 105
 106 division = _Feature((2, 2, 0, "alpha", 2),
 107                     (3, 0, 0, "alpha", 0),
 108                     CO_FUTURE_DIVISION)
 109
 110 absolute_import = _Feature((2, 5, 0, "alpha", 1),
 111                            (2, 7, 0, "alpha", 0),
 112                            CO_FUTURE_ABSOLUTE_IMPORT)
 113
 114 with_statement = _Feature((2, 5, 0, "alpha", 1),
 115                           (2, 6, 0, "alpha", 0),
 116                           CO_FUTURE_WITH_STATEMENT)