python

PYTHON

Volkan Tüfekçi – Gülcan Aydın26.12.2007

History Philosphy UsageGuido van Rossum 1989 Hobby LanguageABC – Modula 3 – Unix/C – Common Lisp - HaskellDislikes:

Difficulty of adding new "primitive" operationsMonolithic, "closed system“, basic I/O operationsIdeosyncratic syntax (all uppercase keywords!)

Aims:ReadabilityRely on the Unix infrastructure and conventions,

without being Unix-boundImportance of programmer effort over computer

effort

12.04.23CSE 494 Volkan TÜFEKÇİ - Gülcan AYDIN 2

History Philosphy Usage(cont.)1991Syntax and semantics are minimalist, while the

standard library is large and comprehensivemulti-paradigm programming language:

object orientation and structured programming -> fully functional programming and aspect-oriented

programming -> by language featurespyDBC and Contracts for Python which allow Design by

Contractdynamic name resolution (late binding)New built-in modules are easily written in C or C++Python philosophy rejects exuberant syntax, such as in PerlPyQt, PyGTK, PyCon, PyPy


History Philosphy Usage(cont.)Nasa, Google, YouTube, BitTorrent, Air

Canada’s Reservation ManagementTurboGears, Django(NewYork Times’ web

site)Maya, BlenderFedora, Gentoo, PardusJython, IronPython



Introduction to O-O PythonPython is an object-oriented programming language. Supports procedural programming with modules and

functions. Generally, the O-O paradigm is suitable when you

want to group state (data) and behavior (code) together in handy packets of functionality.

The procedural paradigm, based on modules and functions, tends to be simpler and is more suitable when you don't need any of the benefits of object-oriented programming.


Syntax All values in Python can be used as logic values. Some of the more

“empty” ones, like [], 0, “” and None represent logical falsity, while most other values (like [0], 1 or “Hello, world”) represent logical truth.

if 0 < month <= 12:doSomething()

Dictionaries 1


• A dictionary in Python is like an instance of the Hashtable class in Java• No duplicate member• No order• Mutable

Dictionaries 2


Lists 1


Lists 2


Lists 3


List & Dictionary Examples


L=[1,2,3,4,5] IMPORTANT: The value will be stored into a range of memory blocks, and what if we do

this? L2=L

It make L2 refers to the same memory blocks where L points to. Example;


List Comprehensions

Tuples


• A tuple is an immutable list. A tuple can not be changed in any way once it is created• Tuples are faster than lists• It makes your code safer if you “write-protect” data• Tuples can be converted into lists, and vice-versa.

Assigning Variables


String Formatting & Concatenating


# 1 membered Tuple!!!

# Strong typed

Importing Modules & Getting Help



String Operation Examples

Modulesfrom UserDict import UserDict


ConstructorA constructor is a method that initializes a newly

created object.The overridden derived-class constructor usually

calls the base-class constructor, to initialize base-class attributes before initializing derived-class attributes.

If a derived class does not define a constructor, the class’s base-class constructor executes when the client creates a new object of the class.


Destructor & Static Variable

Does not actually destroy the object

# Static variable

# 0

# 2

# 0


Static Methods

Property Descriptor


Slots Attribute


>>>8


InheritanceInheritance is a form of software reusability in which

new classes are created from existing classes by absorbing their attributes and behaviors.The new class is referred to as a derived class, inherit

from the class referred to as base class.With single inheritance,a class is derived from one

base class.With multiple inheritance, a derived class inherits from

several base classes.


(cont.)We distinguish between “is-a” relationships and

“has-a” relationships:“Is a” is inheritance. In an “is a” relationship, an object

of a derived-class type may also be treated as an object of the base-class type.

“Has a” is composition. In a “has a” relationship, an object has references to one or more objects of other classes as members.


“is a”Inheritance hierarchy for university community members :


Multiple Inheritance and Name Clash Problem

class Base1: def amethod(self): print "Base1“

class Base2(Base1): pass # pass!!!class Base3:

def amethod(self): print "Base3"

class Derived(Base2, Base3): pass aninstance = Derived( ) aninstance.amethod( ) # prints: "Base1"


Data AbstractionOne of the fundamental principles of good software

engineering is that a client should not need toknow how a class is implemented to use that class.

Python’s use of modules facilitates this dataabstraction—a program can import a class definition and use the class without knowing how theclass is implemented.


EncapsulationNo methods or member variables are protected (or

private or the like) in Python. Encapsulation is pretty much a matter of

programming style. If you really need it, there are naming-conventions that

will allow some privacy. such as; _ _ident Python compiler implicitly changes the identifier into

_classname_ _ident, where classname is the name of the class.


Example of Private Data Access


Abstract Classes

Traceback (most recent call last): b.earnings() raise NotImplementedError, "Cannot call abstract method"NotImplementedError: Cannot call abstract method

Polymorphism


Polymorphism 2


Polymorphism 3


Polymorphism 4


Polymorphism 5


Composition vs. Inheritance

composition of existing classesEmployee is a BirthDate or that an

Employee is a TelephoneNumberEmployee has a BirthDate and that an

Employee has a TelephoneNumber.


“Uses A” and “Knows A” Relationshipsa person object is not a car and a person

object does not contain a car, a person object certainly uses a car

A program uses an object simply by calling a method of that object through a reference.

one object is said to have a knows a relationship with the other object; this is sometimes called an association.


python

Business

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