Python Reference

This is a quick reference, or cheat sheet, to Python (the programming language)

Humour

<Sonium> someone speak python here?
<lucky> HHHHHSSSSSHSSS
<lucky> SSSSS
<Sonium> the programming language

• Flying with Python

Installing Modules

Eggs

If the module comes with a .egg file, this is the preferred installation option

• Visit eggs setup
• (Windows) Add C:\Python25\Scripts to your PATH
• Run easy_install [package] e.g. easy_install MySQL-python

Traditional

• Download the package
• Run python setup.py install

Output

• print = quick and dirty, but adds spaces
• import sys
• sys.stdout.write = best

Strings

• len(s) = length of string

Formatting

• 'format' % ( values )

Conversion characters

• d,i = signed decimal
• u = unsigned decimal
• f,F = floating point
• c = character
• s = string

Modifiers

•  %mc where m is the modifier
• 0 = zero padded
• .3 = 3 decimal places
• - = left justified
• + = precede with + or -

Regexp

• import re
• r = re.compile( r'search' )
• s = r.sub( r'replace', src )

GUI - Tkinter

• A good reference
• Handy tips
• Another good reference (PDF)

tkMessageBox

Quick example:

import tkMessageBox

• Messageboxes for questions

answer = tkMessageBox.askyesno("askyesno", "Hello from askyesno\n1 of 7")

• Change default button. Can be ABORT, RETRY, IGNORE, OK, CANCEL, YES, NO

answer = tkMessageBox.askquestion(title="askquestion", message="Hello from askquestion\n2 of 7", fault=tkMessageBox.NO) 
answer = tkMessageBox.askokcancel("askokcancel", "Hello from askokcancel\n3 of 7") 
answer = tkMessageBox.askretrycancel("askretrycancel", "Hello from askretrycancel\n4 of 7") 

• Messageboxes for info

answer = tkMessageBox.showinfo("showinfo", "Hello from showinfo\n5 of 7") 
answer = tkMessageBox.showerror("showerror", "Hello from showerror\n6 of 7") 
warningMsg = "showwarning" 
answer = tkMessageBox.showwarning("showwarning","Final hello from:\n(%s)\n7 of 7" % warningMsg)

• reference

Canvas

Resizing

• use winfo_width() and winfo_height() to get an up to date widget size

Logging

• import logging
• logging.getLogger().setLevel( logging.DEBUG );
• logging.debug( "note %s", note )

Distributables

py2exe

• classifiers

Multimedia

Audio - tkSnack

• snack manual

Numerical Processing

• Use Numpy, it rocks.

Other Tasks

Base64

import base64
infile = file( "infile", "rb" )
outfile = file( "outfile", "w" )
base64.encode( infile, outfile )
outfile.close()

i18n and l10n

Supporting i18n

• In every string, use _( "string" )
• Call the following function from your main python script:

import gettext
import locale
import logging

def init_localization():
  prepare l10n
  locale.setlocale(locale.LC_ALL, ) # use user's preferred locale
  # take first two characters of country code (?)
  loc = locale.getlocale()
  filename = "res/messages_%s.mo" % locale.getlocale()[0][0:2]

  try:
    logging.debug( "Opening message file %s for locale %s", filename, loc[0] )
    trans = gettext.GNUTranslations(open( filename, "r" ) )
  except IOError:
    logging.debug( "Locale not found. Using default messages" )
    trans = gettext.NullTranslations()

  global _
  _ = trans.gettext

Preparing for translation

• Generate a messages.pot file:

pygettext *.py

• Copy this to a messages.po file
• Send this to translator.
• Translator uses a tool like poedit to fill in the empty strings.

Style

• style guide