1 Outline 7.1 Introduction 7.2 Implementing a Time Abstract Data Type with a Class 7.3 Special...

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Outline7.1 Introduction7.2 Implementing a Time Abstract Data Type with a Class 7.3 Special Attributes 7.4 Controlling Access to Attributes

7.4.1 Get and Set Methods 7.4.2 Private Attributes

7.5 Using Default Arguments With Constructors 7.6 Destructors7.7 Class Attributes 7.8 Composition: Object References as Members of Classes 7.9 Data Abstraction and Information Hiding 7.10 Software Reusability

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Python, short Python, short introductionintroduction

Python, short Python, short introductionintroduction

CSC 667/867CSC 667/867San Francisco State Univ.San Francisco State Univ.

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Abstract• Python Tutorials at http://docs.python.org/tut/• Python is an easy to learn, powerful programming

language. It has efficient high-level data structures and a simple but effective approach to object-oriented programming. Python's elegant syntax and dynamic typing, together with its interpreted nature, make it an ideal language for scripting and rapid application development in many areas on most platforms.

• The Python interpreter is easily extended with new functions and data types implemented in C or C++ (or other languages callable from C). Python is also suitable as an extension language for customizable applications.

• For a description of standard objects and modules, see the Python Library Reference document. The Python Reference Manual gives a more formal definition of the language.

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Features and Strength I• You could write a Unix shell script or Windows

batch files for some of these tasks, but shell scripts are best at moving around files and changing text data, not well-suited for GUI applications or games. You could write a C/C++/Java program, but it can take a lot of development time to get even a first-draft program. Python is simpler to use, available on Windows, MacOS X, and Unix operating systems, and will help you get the job done more quickly.

• Python is simple to use, but it is a real programming language, offering much more structure and support for large programs than shell scripts or batch files can offer.

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Features and Strength II

• high-level data types built in, such as flexible arrays and dictionaries

• Because of its more general data types Python is applicable to a much larger problem domain than Awk or even Perl, yet many things are at least as easy in Python as in those languages.

• Built in modules -file I/O, system calls, sockets, and even interfaces to graphical user interface toolkits like Tk.

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Features & Strength III• Python enables programs to be written

compactly and readably. – the high-level data types allow you to

express complex operations in a single statement;

– statement grouping is done by indentation instead of beginning and ending brackets;

– no variable or argument declarations are necessary.

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Control Flow – if statement

>>> x = int(raw_input("Please enter an integer: ")) >>> if x < 0: ... x = 0 ... print 'Negative changed to zero' ... elif x == 0: ... print 'Zero' ... elif x == 1: ... print 'Single' ... else: ... print 'More' ...

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Control Flow – for statement

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More control statements

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Defining Functions

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Defining Function II

There are more information to read about functions related to scoping, arguments, etc. Check “4.7 More on Defining Functions” from the tutorial

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Data Structures

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More data structures• Tuples• Sequences• Sets• Dictionaries• So, where to look at? Check the

tutorial!

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Modules• A module is a file containing Python definitions and

statements. • The file name is the module name with the suffix .py

appended. • If fibo.py contains fib() function and fib2() function,

then user can invoke them using– Import fibo– fibo.fib()– fibo.fib2()

• Or– from fibo import fib, fib2 – fib()– fib2()

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Modules• The module Search Path using

environment variable, PYTHONPATH– on Unix, this is usually .:/usr/local/lib/python

• ``Compiled'' Python files (for speeding up the modules)– .pyc files– .pyo files (optimized compilation is used)

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Standard Modules

• Python Library Reference at http://docs.python.org/lib/lib.html

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Packages

• Packages are a way of structuring Python's module namespace by using ``dotted module names''.

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Packages• When importing the package, Python searches

through the directories on sys.path looking for the package subdirectory.

• The __init__.py files are required to make Python treat the directories as containing packages;

• Users of the package can import individual modules from the package, for example: – import Sound.Effects.echo– Sound.Effects.echo.echofilter(input, output,

delay=0.7, atten=4)

• An alternative way of importing the submodule is: – from Sound.Effects import echo – from Sound.Effects import *

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Classes

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Standard Library of Python

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Python CGI (1)

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Python CGI (2)

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Python CGI (3)