146a7f8ff6
The metaclass boilerplate is safe to apply en masse. The future import boilerplate needs code to be inspected to be sure that there aren't any py2isms that need to be fixed. Split these two checks so that we can fix them independently Be explicit about which files are grandfathered so we can fix them up one by one
51 lines
2.1 KiB
ReStructuredText
51 lines
2.1 KiB
ReStructuredText
Sanity Tests » from __future__ boilerplate
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==========================================
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Most Python files should include the following boilerplate at the top of the file, right after the
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comment header:
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.. code-block:: python
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from __future__ import (absolute_import, division, print_function)
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This uses Python 3 semantics for absolute vs relative imports, division, and print. By doing this,
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we can write code which is portable between Python 2 and Python 3 by following the Python 3 semantics.
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absolute_import
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---------------
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When Python 2 encounters an import of a name in a file like ``import copy`` it attempts to load
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``copy.py`` from the same directory as the file is in. This can cause problems if there is a python
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file of that name in the directory and also a python module in ``sys.path`` with that same name. In
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that case, Python 2 would load the one in the same directory and there would be no way to load the
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one on ``sys.path``. Python 3 fixes this by making imports absolute by default. ``import copy``
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will find ``copy.py`` from ``sys.path``. If you want to import ``copy.py`` from the same directory,
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the code needs to be changed to perform a relative import: ``from . import copy``.
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.. seealso::
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* `Absolute and relative imports <https://www.python.org/dev/peps/pep-0328>`_
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division
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--------
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In Python 2, the division operator (``/``) returns integer values when used with integers. If there
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was a remainder, this part would be left off (aka, `floor division`). In Python 3, the division
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operator (``/``) always returns a floating point number. Code that needs to calculate the integer
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portion of the quotient needs to switch to using the floor division operator (`//`) instead.
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.. seealso::
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* `Changing the division operator <https://www.python.org/dev/peps/pep-0238>`_
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print_function
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--------------
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In Python 2, :func:`python:print` is a keyword. In Python 3, :func:`python3:print` is a function with different
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parameters. Using this ``__future__`` allows using the Python 3 print semantics everywhere.
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.. seealso::
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* `Make print a function <https://www.python.org/dev/peps/pep-3105>`_
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