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1# Copyright 2016 Google Inc. All rights reserved.
2#
3# Licensed under the Apache License, Version 2.0 (the "License");
4# you may not use this file except in compliance with the License.
5# You may obtain a copy of the License at
6#
7#     http://www.apache.org/licenses/LICENSE-2.0
8#
9# Unless required by applicable law or agreed to in writing, software
10# distributed under the License is distributed on an "AS IS" BASIS,
11# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
12# See the License for the specific language governing permissions and
13# limitations under the License.
14
15""" A tiny version of `six` to help with backwards compability. Also includes
16 compatibility helpers for numpy. """
17
18import sys
19import imp
20
21PY2 = sys.version_info[0] == 2
22PY26 = sys.version_info[0:2] == (2, 6)
23PY27 = sys.version_info[0:2] == (2, 7)
24PY275 = sys.version_info[0:3] >= (2, 7, 5)
25PY3 = sys.version_info[0] == 3
26PY34 = sys.version_info[0:2] >= (3, 4)
27
28if PY3:
29    string_types = (str,)
30    binary_types = (bytes,bytearray)
31    range_func = range
32    memoryview_type = memoryview
33    struct_bool_decl = "?"
34else:
35    string_types = (unicode,)
36    if PY26 or PY27:
37        binary_types = (str,bytearray)
38    else:
39        binary_types = (str,)
40    range_func = xrange
41    if PY26 or (PY27 and not PY275):
42        memoryview_type = buffer
43        struct_bool_decl = "<b"
44    else:
45        memoryview_type = memoryview
46        struct_bool_decl = "?"
47
48# Helper functions to facilitate making numpy optional instead of required
49
50def import_numpy():
51    """
52    Returns the numpy module if it exists on the system,
53    otherwise returns None.
54    """
55    try:
56        imp.find_module('numpy')
57        numpy_exists = True
58    except ImportError:
59        numpy_exists = False
60
61    if numpy_exists:
62        # We do this outside of try/except block in case numpy exists
63        # but is not installed correctly. We do not want to catch an
64        # incorrect installation which would manifest as an
65        # ImportError.
66        import numpy as np
67    else:
68        np = None
69
70    return np
71
72
73class NumpyRequiredForThisFeature(RuntimeError):
74    """
75    Error raised when user tries to use a feature that
76    requires numpy without having numpy installed.
77    """
78    pass
79
80
81# NOTE: Future Jython support may require code here (look at `six`).
82