[Python-checkins] r88348 - python/branches/py3k/Doc/howto/pyporting.rst
antoine.pitrou
python-checkins at python.org
Sat Feb 5 13:13:38 CET 2011
Author: antoine.pitrou
Date: Sat Feb 5 13:13:38 2011
New Revision: 88348
Log:
Everybody hates this one :) (bytes indexing)
Modified:
python/branches/py3k/Doc/howto/pyporting.rst
Modified: python/branches/py3k/Doc/howto/pyporting.rst
==============================================================================
--- python/branches/py3k/Doc/howto/pyporting.rst (original)
+++ python/branches/py3k/Doc/howto/pyporting.rst Sat Feb 5 13:13:38 2011
@@ -367,6 +367,37 @@
BytesWarning: Comparison between bytes and string
+Indexing bytes objects
+''''''''''''''''''''''
+
+Another potentially surprising change is the indexing behaviour of bytes
+objects in Python 3::
+
+ >>> b"xyz"[0]
+ 120
+
+Indeed, Python 3 bytes objects (as well as :class:`bytearray` objects)
+are sequences of integers. But code converted from Python 2 will often
+assume that indexing a bytestring produces another bytestring, not an
+integer. To reconcile both behaviours, use slicing::
+
+ >>> b"xyz"[0:1]
+ b'x'
+ >>> n = 1
+ >>> b"xyz"[n:n+1]
+ b'y'
+
+The only remaining gotcha is that an out-of-bounds slice returns an empty
+bytes object instead of raising ``IndexError``:
+
+ >>> b"xyz"[3]
+ Traceback (most recent call last):
+ File "<stdin>", line 1, in <module>
+ IndexError: index out of range
+ >>> b"xyz"[3:4]
+ b''
+
+
``__str__()``/``__unicode__()``
'''''''''''''''''''''''''''''''
In Python 2, objects can specify both a string and unicode representation of
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