Apprenez à programmer en Python

Foreword

Notes. Python 3. From Le Livre du Zéro, Simple IT, 2011.

---

Shebang Line

_{shebang, top, file, environment, language, kernel, python2, python 2, python3, python 3, utf, utf8, utf-8}

Other names: sha-bang, hashbang, pound-bang, hash-pling.

At the top of scripts

• In Windows, Python 2:
  • python.
• Windows, Python 3:
  • python 3.
• UNIX, Python 2:
  • #!/usr/bin/env python.
• UNIX, Python 3:
  • #!/usr/bin/env python 3.
• Add:
  • # -*coding: utf-8 -*-.
  • # -*coding: latin-1 -*-.

Launch a script

• In Windows, Python 2:
  • python script.py.
  • py script.py.
  • py -2 script.py.
  • py -2.7 script.py.
• In UNIX, Python 2:
  • python script.py.
• In Windows, Python 3:
  • py -3 script.py.
  • py -3.5 script.py.
• In UNIX, Python 3:
  • python3 script.py.

Launch the shell/bash

• The shell, Python 2:
  • python.
  • py -2.
  • py -2.7.
• The bash, Python 2:
  • python.
  • python2.
• The shell, Python 3:
  • py -3.
  • py -3.5.
• The bash, Python 3:
  • python3.

Chapter 8, Exceptions

Basic.

• try: block.
• except errors.
• else:.
• finally:.
• assert tests and conditions.
• raise an exception.

Chapter 10, Strings

Basic.

A "string".

• str() function.
• upper() and lower() methods; upper/lower characters.
• capitalize() method; first-letter upper character.
• left(), right(), center() methods.
• strip(), lstrip(), rstrip() methods; remove white space.
• format() method.
• count() method.
• find() method.
• replace() method.
• [:] to subset a string.
• while loop on a string.

Chapter 11, Lists and Tuples 1

Basic.

_{delete, length, size}

Lists are mutable; can add or remove elements from a list; can change the order of elements.

A [list].

• insert() method.
• append() method.
• extends() method.
• del() function; delete an indexed element.
• remove() method; remove an occurrence.
• len() function; length.
• for loop, in a list.
• enumerate() function; return the index and elements.

Tuples are immutable; cannot be modified.

(tuple).

Chapter 12, Lists and Tuples 2

Basic.

_{flexible, function, flexibility, parameter}

With lists, functions can have an undetermined number of parameters (very flexible!):

• def my_function(*parameter):.
• def my_function(a, b, *parameter):.

Strings and lists. Create, split, loop through a sequence. Even in a list of list.

• split() method.
• join() method.
• for loop, in a list.

Find the type() of a variable (integer, float, boolean, etc.)

Chapter 13, Dictionaries

Basic.

_{dictionary, flexible, function, flexibility, parameter}

Dictionaries are mutable; you can add or remove elements from a dictionary; order of elements is unimportant.

One-entry dictionary: {'key': 'value'}.

With dictionaries, functions can have an undetermined number of parameters (very flexible!):

• def my_function(**parameter):.
• def my_function(a, b, **parameter):.

Combine lists and dictionaries in a function with an undetermined number of parameters:

• def my_function(*, parameter, **parameter):.

• def my_function(a, b, *parameter, **parameter):.

• del dict['key'] function; delete.

• pop() method; pop out an element.
• for loop, in a dictionary.
• in dict.keys() method; extract the dictionary dict in order.
• in dict.values() method; extract the values from dictionary dict.
• in dict.items() method to extract the keys and values from dictionary dict.

Chapter 14, Files

Basic.

os module. Perform bash, shell operations such as opening, closing, reading, and writing files. Manage relative and absolute path. In UNIX and Windows.

• open() method.
• close() method.
• read() method.

• write() method.

• with/as method; create aliases.

pickle module. Record objects in a file and retrieve them.

• Pickler() method.

Chapter 17, Classes and docstrings

Basic.

_{class, instance, self}

docstring module. Under a Class, a docstring documents the class. Under def __init__():, a docstring documents the attributes. Under def function():, a docstring documents the use of the function or class method, under variable, a docstring documents the use of the variable.

object.__doc__ method; accesses the docstring.

__all__ function; displays the list of public names (of objects).

pydoc module. Displays information about an object with the help(object) function.

dir(object) function; returns an object’s parameters (all the attributes, methods, functions).

object.__dict__ method; returns an object’s attributes.

object.__dict__["att_a"] = "att_b" changes an object’s attribute.

Chapter 18, (Class) Properties

Basic.

_{instance, constructor}

More about the def __init__(): constructor.

Chapter 19, Special Methods

Basic.

_{mathematics, display results}

• def __repr__(self): modifies the way an object is displayed when called.

• def __str__(self): method modifies the way an object is displayed when printed.

• def __getattr__(): defines a message when an inexistent object’s attributes is called (like a try block) vs the built-in object.__dict__

• def __setattr__(): does the same when an object’s attribute is modified vs the built-in object.__dict__["att_a"] = "att_b"
• def __delattr__(): does the same when an object’s attribute is deleted.

• def __hasattr__(): returns true or false if the attribute exists.

• def __getitem__():, def __setitem__():, and def __delitem__(): all define what to do when we write, respectively: object[index], object[index] = value, and del object[index].

• object.__contains__ checks out if a list contains a specific element; like in

• object.__len__() shows the size of an object.

• object.__add__(4) is equivalent to object + 4;

• def __add(): as well.
• object.__sub__() or -.
• __mul__ or *.
• __truediv__ or /.
• __floordiv__ or //.
• __mod__ or %.
• __pow__ or **.
• __radd__, __iadd__, etc.
• def __eq__(): or ==.
• __ne__ or !=.
• __gt__ or >.
• __ge__ or >=.
• __lt__ or <.

• __le__ or <=.

• pickle module. Record objects in a file and retrieve them.

• __getstate__ method.

• __setstate__ method.

Chapter 20, Heritage

Basic.

_except

Class heritage transfers all attributes, parameters and methods from a class to a subclass.

• issubclass verifies (true or false) if a class is a subclass of another class.
• isinstance verifies if an object comes from a class.

A subclass can inherit from two or more classes (multiple heritage).

More exceptions in a try block, except, heritage, AttributeError, Exception, BaseException, and resolution.

Exceptions are classes with hierarchy.

Chapter 21, The for Loop Again

Basic.

Related to the for loop and how to dig deeper into the iterator with __iter__ and __next__.

Iterator can also skip items in a list: iterate from 1 to 5, them jump to 10 and go on. A sort of conditional break. For that, we must generate intervals with yield.

Chapter 23, Decorators

Advanced!

_{simplify code}

A decorator simplifies:

def function(...):
    ...
...
function = decorator (function)

With:

@decorator
def function(...):
    ...

There are decorators without parameters, with parameters, applied to classes; chained together.

Use:

1. Limit a class instance to only one instance or one object (a singleton).
2. Add more control on the type of data going into functions.

Chapter 24, Metaclasses

Advanced!

__init__ initiates an object with attributes, but does not create the object itself.

It is done by coding a new instance or with __new__. The method is useful to create immutable objects that cannot be modified.

Create dynamic classes with type.

Chapter 25, Regular Expressions

Basic.

_{regex, string, search, beginning, end, replace, occurrence, character, class, group, number, numbered group, name, named}

re module.

Chapter 26, Time

Basic.

_{date, time, year, month, day, hour, minute, second, time zone, timezone, time delta, timedelta, time stamp, timestamp, format}

time module and datetime module.

Chapter 27, System Programming

Basic.

_{input, output, stdin, stdout, open, close, read, write, directory, file}

sys module and os module. Access system variables and control the operating system.

signal module. Read process signals sent to programs (such as stopping and exiting).

Access and control the OS console, enter CLI arguments, program actions usually done with the mouse and the keyboard.

system module, related to os.

• os.system('ls') on Linux.
• os.system('dir') on Windows.

For example:

import os

cmd = os.popen('ls')

cmd
cmd.read()

Chapter 28, Maths

Basic.

math module.

Enables new methods in arithmetics, trigonometry, rounding: pow(), sqrt(), exp(), fabs(), radians(), degrees(), ceil(), floor(), trunc(), etc

fractions module.

Fraction(), from_float(), etc.

random module.

random(), randrange(), randint(), choice(), etc.

Chapter 29, Password Management

Web framework.

getpass module.

Receive a password, cypher a password, etc.

Chapter 30, Network

Web framework.

_{tcp, protocol, client, server, connection, http, port, socket, connect,}

socket module and select module.

Chapter 31, Tkinter

Software, application.

_{gui, graphic, interface, window, button, interactive, box, toggle, widget, labels, square, checkbox, list, command}

Tkinter module.

Chapter 33, Distribute Scripts and Programs

Basic.

Method 1: Executable File

cx_freeze creates a standalone executable file. cx_Freeze is portable (Windows, Linux, Mac OS X), compatible with Py -2 and Py -3, simple, fast, flexible.

Download, install, use the cxfreeze script

Alternative: py2exe (Windows only).

Method 2: Setup File

The traditional way of distributing a code and a more powerful approach.

Chapter 34, PEP

Basic.

• PEP 20: The Zen of Python.
• PEP 8: coding conventions.
  • identation, tabulation, line length, line spacing, encoding, importing, spacing, commenting, naming, coding comparisons.
• PEP 257: documentation and docstrings.

Chapter 35, More…

Basic.

• References.
• Wiki.
• PEP.
• Documentation.
• Basic library
• Additional libraries.
  • graphical interfaces: Tk, PyQT, PyGTK, wx Python.
  • web framworks: Django, CherryPy.
  • networks: Twisted.
• Index.