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---
format: rst
toc: no
...
======================
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. Use it like::
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
-------------
Runsnake seems to be unmaintained... `snakeviz` is the new thing?
Example session::
$ python -m cProfile -o ./dump.profile myscript.py --script-option blah
$ # run to completion or Ctrl-C, then
$ runsnakerun ./dump.profile
# or
$ snakeviz ./dump.profile
nosetests
-------------
NOTE: by default I now use pytest instead of nose
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.
Debian Default Python
----------------------
Keep in mind that this can break some system things (eg, arandr, some cups
things).
To make Python 3.4 the default for `python` system-wide, do something like:
sudo update-alternatives --install /usr/bin/python python /usr/bin/python3.4 2
For an individual user you can also just create a `python` alias. See also:
http://linuxconfig.org/how-to-change-from-default-to-alternative-python-version-on-debian-linux
Nice Packages
--------------
subprocess/pexpect: https://github.com/kennethreitz/delegator.py
time/datetime: https://github.com/crsmithdev/arrow
tsv: https://github.com/kennethreitz/tablib
simple HTML scraping: https://github.com/michaelhelmick/lassie
sqlite3dbm is a library to back a python dict with sqlite3 on disk
pytest
-----------
pytest sort of "just works" if you put test files under `./tests/`. If you want
crude file imports, skipping directories, and including `test_*` functions from
any python file (not just those with `test_*.py`, install `pytest-pythonpath`
and create a `pytest.ini` like:
[pytest]
python_paths = .
python_files = *.py
norecursedirs = .svn _build tmp*
Need to mock? <https://blog.fugue.co/2016-02-11-python-mocking-101.html>
Debugging Memory Usage
------------------------
Most helpful tools I found were `psutil` and `pympler` (both need to be
installed).
import os, psutil
process = psutil.Process(os.getpid())
print(process.memory_info().rss)
# ... do some stuff ...
print(process.memory_info().rss)
and
from pympler import tracker
tr = tracker.SummaryTracker()
tr.print_diff()
# ... do some stuff ...
tr.print_diff()
|
