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Issue #20208: Clarify some things in the Python porting HOWTO. 

Thanks to Rodrigo Bernardo Pimentel, Ondřej Čertík, and Dmitry
Shachnev for the feedback leading to the changes.
This commit is contained in:
Brett Cannon 2014-01-17 11:45:01 -05:00
parent c089f70b54
commit f0996a9970
1 changed files with 11 additions and 9 deletions
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Doc/howto/pyporting.rst
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@ -151,15 +151,17 @@ older).
``from __future__ import unicode_literals`` ``from __future__ import unicode_literals``
''''''''''''''''''''''''''''''''''''''''''' '''''''''''''''''''''''''''''''''''''''''''
If you choose not to use this future statement you should then mark all of your If you choose to use this future statement then all string literals in
Python 2 will be assumed to be Unicode (as is already the case in Python 3).
If you choose not to use this future statement then you should mark all of your
text strings with a ``u`` prefix and only support Python 3.3 or newer. But you text strings with a ``u`` prefix and only support Python 3.3 or newer. But you
are **strongly** advised to do one or the other (six_ provides a function in are **strongly** advised to do one or the other (six_ provides a function in
case you don't want to use the future statement **and** you want to support case you don't want to use the future statement **and** you want to support
Python 3.2 or older). Python 3.2 or older).
Bytes literals Bytes/string literals
'''''''''''''' '''''''''''''''''''''
This is a **very** important one. Prefix Python 2 strings that This is a **very** important one. Prefix Python 2 strings that
are meant to contain bytes with a ``b`` prefix to very clearly delineate are meant to contain bytes with a ``b`` prefix to very clearly delineate
@ -504,12 +506,13 @@ your time and effort to port your tests to :mod:`unittest`.
Update ``map`` for imbalanced input sequences Update ``map`` for imbalanced input sequences
''''''''''''''''''''''''''''''''''''''''''''' '''''''''''''''''''''''''''''''''''''''''''''
With Python 2, ``map`` would pad input sequences of unequal length with With Python 2, when ``map`` was given more than one input sequence it would pad
`None` values, returning a sequence as long as the longest input sequence. the shorter sequences with `None` values, returning a sequence as long as the
longest input sequence.
With Python 3, if the input sequences to ``map`` are of unequal length, ``map`` With Python 3, if the input sequences to ``map`` are of unequal length, ``map``
will stop at the termination of the shortest of the sequences. For full will stop at the termination of the shortest of the sequences. For full
compatibility with ``map`` from Python 2.x, also wrap the sequences in compatibility with ``map`` from Python 2.x, wrap the sequence arguments in
:func:`itertools.zip_longest`, e.g. ``map(func, *sequences)`` becomes :func:`itertools.zip_longest`, e.g. ``map(func, *sequences)`` becomes
``list(map(func, itertools.zip_longest(*sequences)))``. ``list(map(func, itertools.zip_longest(*sequences)))``.
@ -518,9 +521,8 @@ Eliminate ``-3`` Warnings
When you run your application's test suite, run it using the ``-3`` flag passed When you run your application's test suite, run it using the ``-3`` flag passed
to Python. This will cause various warnings to be raised during execution about to Python. This will cause various warnings to be raised during execution about
things that 2to3 cannot handle automatically (e.g., modules that have been things that are semantic changes between Python 2 and 3. Try to eliminate those
removed). Try to eliminate those warnings to make your code even more portable warnings to make your code even more portable to Python 3.
to Python 3.
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