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     "print_function",
  57     "unicode_literals",
  58 ]
  59
  60 __all__ = ["all_feature_names"] + all_feature_names
  61
  62 # The CO_xxx symbols are defined here under the same names used by
  63 # compile.h, so that an editor search will find them here.  However,
  64 # they're not exported in __all__, because they don't really belong to
  65 # this module.
  66 CO_NESTED            = 0x0010   # nested_scopes
  67 CO_GENERATOR_ALLOWED = 0        # generators (obsolete, was 0x1000)
  68 CO_FUTURE_DIVISION   = 0x2000   # division
  69 CO_FUTURE_ABSOLUTE_IMPORT = 0x4000 # perform absolute imports by default
  70 CO_FUTURE_WITH_STATEMENT  = 0x8000   # with statement
  71 CO_FUTURE_PRINT_FUNCTION  = 0x10000   # print function
  72 CO_FUTURE_UNICODE_LITERALS = 0x20000 # unicode string literals
  73
  74 class _Feature:
  75     def __init__(self, optionalRelease, mandatoryRelease, compiler_flag):
  76         self.optional = optionalRelease
  77         self.mandatory = mandatoryRelease
  78         self.compiler_flag = compiler_flag
  79
  80     def getOptionalRelease(self):
  81         """Return first release in which this feature was recognized.
  82
  83         This is a 5-tuple, of the same form as sys.version_info.
  84         """
  85
  86         return self.optional
  87
  88     def getMandatoryRelease(self):
  89         """Return release in which this feature will become mandatory.
  90
  91         This is a 5-tuple, of the same form as sys.version_info, or, if
  92         the feature was dropped, is None.
  93         """
  94
  95         return self.mandatory
  96
  97     def __repr__(self):
  98         return "_Feature" + repr((self.optional,
  99                                   self.mandatory,
 100                                   self.compiler_flag))
 101
 102 nested_scopes = _Feature((2, 1, 0, "beta",  1),
 103                          (2, 2, 0, "alpha", 0),
 104                          CO_NESTED)
 105
 106 generators = _Feature((2, 2, 0, "alpha", 1),
 107                       (2, 3, 0, "final", 0),
 108                       CO_GENERATOR_ALLOWED)
 109
 110 division = _Feature((2, 2, 0, "alpha", 2),
 111                     (3, 0, 0, "alpha", 0),
 112                     CO_FUTURE_DIVISION)
 113
 114 absolute_import = _Feature((2, 5, 0, "alpha", 1),
 115                            (2, 7, 0, "alpha", 0),
 116                            CO_FUTURE_ABSOLUTE_IMPORT)
 117
 118 with_statement = _Feature((2, 5, 0, "alpha", 1),
 119                           (2, 6, 0, "alpha", 0),
 120                           CO_FUTURE_WITH_STATEMENT)
 121
 122 print_function = _Feature((2, 6, 0, "alpha", 2),
 123                           (3, 0, 0, "alpha", 0),
 124                           CO_FUTURE_PRINT_FUNCTION)
 125
 126 unicode_literals = _Feature((2, 6, 0, "alpha", 2),
 127                             (3, 0, 0, "alpha", 0),
 128                             CO_FUTURE_UNICODE_LITERALS)