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======================
Python
======================
iPython tricks
--------------
Use the ``cpaste'' command to copy in blocks of raw python code, even if the
indenting is a little weird.
Style
-------
Python PEP-008 <http://www.python.org/dev/peps/pep-0008/>: Style Guide for
Python Code
pylint <http://pypi.python.org/pypi/pylint>, a Python syntax checker. Very
verbose, use pylint -E (errors only) or at least pylint -r no (no report). Eg,
"pylint -r no file.py -d W0614 -d C -d R".
For docstring documentation, refer to
PEP-257<http://www.python.org/dev/peps/pep-0257/> and the Sphinx
documentation<http://packages.python.org/an_example_pypi_project/sphinx.html
>; specifically, document script functionality in a top level (above imports,
below any hashbang) docstring.
Use leading "#:" style comments to document important non-object/non-function
element definitions (eg, static variables) in a way that will get pulled out
into Sphinx. Use "Google-style" function argument/return documentation instead
of "Sphinx style". For example:
def public_fn_with_googley_docstring(name, state=None):
"""This function does something.
Args:
name (str): The name to use.
Kwargs:
state (bool): Current state to be in.
Returns:
int. The return code::
0 -- Success!
1 -- No good.
2 -- Try again.
Raises:
AttributeError, KeyError
A really great idea. A way you might use me is
>>> print public_fn_with_googley_docstring(name='foo', state=None)
0
BTW, this always returns 0. **NEVER** use with :class:`MyPublicClass`.
"""
return 0
autopep8 is a tool to automatically pep8-ify a file:
sudo pip install autopep8
autopep8 --in-place --select=W293,W191,W291 *.py
pep8radius is sort of similar, but only applies to code that you are going to
commit (using VCS info).
Packaging
-----------
Flask app packaging advice, including ``MANIFEST.in`` and non-PyPi dependancy
advice: http://flask.pocoo.org/docs/patterns/distribute/
Use ``console_scripts`` in ``setup.py`` to install system-wide scripts:
http://packages.python.org/distribute/setuptools.html#automatic-script-creation
For debian packaging, use [stdeb](http://pypi.python.org/pypi/stdeb)
(via [stackoverflow thread](http://stackoverflow.com/questions/7110604/standard-way-to-create-debian-packages-for-distributing-python-programs)).
For notes on pip vs. setup.py dependencies:
https://caremad.io/blog/setup-vs-requirement/
"Fucking" String Encoding
---------------------------
(str/unicode errors in python are very prevalent and give me the rage)
The ``codecs`` package has some helpers; see for example
``open(f,mode,encoding)``.
ASCII
----------------
'ord' is the function that takes a single ASCII character and returns the value
number (as an int).
RunSnakeRun
-------------
$ python -m cProfile -o ./dump.profile myscript.py --script-option blah
$ # run to completion or Ctrl-C, then
$ runsnakerun ./dump.profile
nosetests
-------------
To do minimal tests without wrapping everything in a class, import assert
functions from nose.tools, eg:
from nose.tools import assert_raises, assert_equal
To do interactive pdb debugging, simply:
$ nosetests --pdb
# or sometimes:
$ nosetests --pdb-failures
pdb
-------
To debug a script (interactive prompt on exception):
python -m pdb myscript.py
or in-line, always at a particular point:
import pdb; pdb.set_trace()
Use ipdb (debian: python-ipdb) instead of pdb to get a nicer IPython prompt.
Python 3 Porting
-------------------
To help port and support both Python 2.7 and 3.0+, start with an import::
from __future__ import absolute_import, division, print_function
str/bytes/unicode is indeed the major porting challenge. Using bytearrays
helps. Use ``b'asdf'`` style byte array definitions for most low-level
constants.
``struct.unpack()`` wants doesn't allow ``bytearray()``; use ``bytes()``
instead.
Make sure ``rase Exception ("Message here")`` style is used everywhere, instead
of ``raise Exception, "Message here"``.
There was some change in comparison between None and integers, which makes
``if args.verbose > 0`` break. Use ``if args.verbose and args.verbose > 1``
instead.
|
