1 from __future__ import absolute_import, division, print_function

     2 

     3 import sys

     4 import types

     5 

     6 

     7 PY2 = sys.version_info[0] == 2

     8 

     9 

    10 if PY2:

    11     from UserDict import IterableUserDict

    12 

    13     # We 'bundle' isclass instead of using inspect as importing inspect is

    14     # fairly expensive (order of 10-15 ms for a modern machine in 2016)

    15     def isclass(klass):

    16         return isinstance(klass, (type, types.ClassType))

    17 

    18     # TYPE is used in exceptions, repr(int) is different on Python 2 and 3.

    19     TYPE = "type"

    20 

    21     def iteritems(d):

    22         return d.iteritems()

    23 

    24     def iterkeys(d):

    25         return d.iterkeys()

    26 

    27     # Python 2 is bereft of a read-only dict proxy, so we make one!

    28     class ReadOnlyDict(IterableUserDict):

    29         """

    30         Best-effort read-only dict wrapper.

    31         """

    32 

    33         def __setitem__(self, key, val):

    34             # We gently pretend we're a Python 3 mappingproxy.

    35             raise TypeError("'mappingproxy' object does not support item "

    36                             "assignment")

    37 

    38         def update(self, _):

    39             # We gently pretend we're a Python 3 mappingproxy.

    40             raise AttributeError("'mappingproxy' object has no attribute "

    41                                  "'update'")

    42 

    43         def __delitem__(self, _):

    44             # We gently pretend we're a Python 3 mappingproxy.

    45             raise TypeError("'mappingproxy' object does not support item "

    46                             "deletion")

    47 

    48         def clear(self):

    49             # We gently pretend we're a Python 3 mappingproxy.

    50             raise AttributeError("'mappingproxy' object has no attribute "

    51                                  "'clear'")

    52 

    53         def pop(self, key, default=None):

    54             # We gently pretend we're a Python 3 mappingproxy.

    55             raise AttributeError("'mappingproxy' object has no attribute "

    56                                  "'pop'")

    57 

    58         def popitem(self):

    59             # We gently pretend we're a Python 3 mappingproxy.

    60             raise AttributeError("'mappingproxy' object has no attribute "

    61                                  "'popitem'")

    62 

    63         def setdefault(self, key, default=None):

    64             # We gently pretend we're a Python 3 mappingproxy.

    65             raise AttributeError("'mappingproxy' object has no attribute "

    66                                  "'setdefault'")

    67 

    68         def __repr__(self):

    69             # Override to be identical to the Python 3 version.

    70             return "mappingproxy(" + repr(self.data) + ")"

    71 

    72     def metadata_proxy(d):

    73         res = ReadOnlyDict()

    74         res.data.update(d)  # We blocked update, so we have to do it like this.

    75         return res

    76 

    77 else:

    78     def isclass(klass):

    79         return isinstance(klass, type)

    80 

    81     TYPE = "class"

    82 

    83     def iteritems(d):

    84         return d.items()

    85 

    86     def iterkeys(d):

    87         return d.keys()

    88 

    89     def metadata_proxy(d):

    90         return types.MappingProxyType(dict(d))