Compatibility wrapper module to make rsa work with various versions of Python.

2 files changed, 116 insertions, 0 deletions

diff --git a/rsa/_compat.py b/rsa/_compat.py
new file mode 100644
index 0000000..162f47e
--- /dev/null
+++ b/rsa/_compat.py
@@ -0,0 +1,99 @@
+# -*- coding: utf-8 -*-
+#
+#  Copyright 2011 Sybren A. Stüvel <sybren@stuvel.eu>
+#
+#  Licensed under the Apache License, Version 2.0 (the "License");
+#  you may not use this file except in compliance with the License.
+#  You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+#  Unless required by applicable law or agreed to in writing, software
+#  distributed under the License is distributed on an "AS IS" BASIS,
+#  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+#  See the License for the specific language governing permissions and
+#  limitations under the License.
+
+'''Python compatibility wrappers.'''
+
+
+from __future__ import absolute_import
+
+from struct import pack
+
+try:
+    # < Python3
+    unicode_type = unicode
+    have_python3 = False
+except NameError:
+    # Python3.
+    unicode_type = str
+    have_python3 = True
+
+# Fake byte literals.
+if str is unicode_type:
+    def byte_literal(s):
+        return s.encode('latin1')
+else:
+    def byte_literal(s):
+        return s
+
+# ``long`` is no more. Do type detection using this instead.
+try:
+    integer_types = (int, long)
+except NameError:
+    integer_types = (int,)
+
+b = byte_literal
+
+try:
+    # Python 2.6 or higher.
+    bytes_type = bytes
+except NameError:
+    # Python 2.5
+    bytes_type = str
+
+
+def is_bytes(obj):
+    """
+    Determines whether the given value is a byte string.
+
+    :param obj:
+        The value to test.
+    :returns:
+        ``True`` if ``value`` is a byte string; ``False`` otherwise.
+    """
+    return isinstance(obj, bytes_type)
+
+
+def is_integer(obj):
+    """
+    Determines whether the given value is an integer.
+
+    :param obj:
+        The value to test.
+    :returns:
+        ``True`` if ``value`` is an integer; ``False`` otherwise.
+    """
+    return isinstance(obj, integer_types)
+
+
+def byte(num):
+    """
+    Converts a number between 0 and 255 (both inclusive) to a base-256 (byte)
+    representation.
+
+    Use it as a replacement for ``chr`` where you are expecting a byte
+    because this will work on all current versions of Python::
+
+        >>> byte(0)
+        '\x00'
+        >>> byte(255)
+        '\xff'
+
+    :param num:
+        An unsigned integer between 0 and 255 (both inclusive).
+    :returns:
+        A single byte.
+    """
+    return pack("B", num)
diff --git a/tests/test_compat.py b/tests/test_compat.py
new file mode 100644
index 0000000..3652c82
--- /dev/null
+++ b/tests/test_compat.py
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+# -*- coding: utf-8 -*-
+
+import unittest2
+import struct
+
+from rsa._compat import is_bytes, byte
+
+class Test_byte(unittest2.TestCase):
+    def test_byte(self):
+        for i in range(256):
+            byt = byte(i)
+            self.assertTrue(is_bytes(byt))
+            self.assertEqual(ord(byt), i)
+
+    def test_raises_StructError_on_overflow(self):
+        self.assertRaises(struct.error, byte, 256)
+        self.assertRaises(struct.error, byte, -1)