add byte2int (fixes #26)

4 files changed, 17 insertions, 0 deletions

diff --git a/CHANGES b/CHANGES
index 9387ce6..f721a40 100644
--- a/CHANGES
+++ b/CHANGES
@@ -6,6 +6,8 @@ This file lists the changes in each six version.
 Development version
 -------------------
 
+- Issue #26: Add byte2int function which complements int2byte.
+
 - Add a PY2 constant with obvious semantics.
 
 - Add helpers for indexing and iterating over bytes: iterbytes and indexbytes.
diff --git a/documentation/index.rst b/documentation/index.rst
index d60328a..3755d52 100644
--- a/documentation/index.rst
+++ b/documentation/index.rst
@@ -330,6 +330,12 @@ string data in all Python versions.
    equivalent to :func:`py2:chr` in Python 2 and ``bytes((i,))`` in Python 3.
 
 
+.. function:: byte2int(bs)
+
+   Converts the first byte of *bs* to an integer.  This is equivalent to
+   ``ord(bs[0])`` on Python 2 and ``bs[0]`` on Python 3.
+
+
 .. function:: indexbytes(buf, i)
 
    Return the byte at index *i* of *buf* as an integer.  This is equivalent to
diff --git a/six.py b/six.py
index 127036e..831d5f7 100644
--- a/six.py
+++ b/six.py
@@ -311,6 +311,7 @@ if PY3:
     else:
         # This is about 2x faster than the implementation above on 3.2+
         int2byte = operator.methodcaller("to_bytes", 1, "big")
+    byte2int = operator.itemgetter(0)
     indexbytes = operator.getitem
     iterbytes = iter
     import io
@@ -322,6 +323,8 @@ else:
     def u(s):
         return unicode(s, "unicode_escape")
     int2byte = chr
+    def byte2int(bs):
+        return ord(bs[0])
     def indexbytes(buf, i):
         return ord(buf[i])
     def iterbytes(buf):
diff --git a/test_six.py b/test_six.py
index 7e15a1c..3983528 100644
--- a/test_six.py
+++ b/test_six.py
@@ -356,6 +356,12 @@ def test_int2byte():
     py.test.raises((OverflowError, ValueError), six.int2byte, 256)
 
 
+def test_byte2int():
+    assert six.byte2int(six.b("\x03")) == 3
+    assert six.byte2int(six.b("\x03\x04")) == 3
+    py.test.raises(IndexError, six.byte2int, six.b(""))
+
+
 def test_bytesindex():
     assert six.indexbytes(six.b("hello"), 3) == ord("l")