Phần 26 KHÓA ĐÀO TẠO TÍNH TOÁN ỔN ĐỊNH VÀ ỨNG DỤNG TRÊN PHẦN MỀM PSSE CHO KỸ SƯ HỆ THỐNG ĐIỆN (Ngôn ngữ lập trình Python và ứng dụng trên Phần mềm PSSE)

KHÓA ĐÀO TẠO TÍNH TOÁN ỔN ĐỊNH VÀ ỨNG DỤNG TRÊN PHẦN MỀM PSSE CHO KỸ SƯ HỆ THỐNG ĐIỆN (Ngôn ngữ lập trình Python và ứng dụng trên Phần mềm PSSE): • Basic Syntax• Variables• Control Flow Tools• BuiltIn Functions and Methods• UserDefined Functions• Files and Directories

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POWER SYSTEM STABILITY CALCULATION TRAINING

D 13 I t d ti t P th Day 13 - Introduction to Python

December 4, 2013 Prepared by: Mohamed El Chehaly

OUTLINE OUTLINE

• Basic Syntax

• Variables

• Control Flow Tools

• Built-In Functions and Methods

• User-Defined Functions

• Files and Directories

BASIC SYNTAX eBook for You

Introduction

 Easy to learn, powerful programming tool

 Efficient high level data structures

 Simple but effective approach to

object-oriented programming

 Programs in Python much shorter than

equivalent C C++ or Java programs:

 Complex operations can be expressed in a single

statement

 Statement grouping is done by indentation instead

of beginning and ending brackets

Introduction

the interpreter and you do not need to

the interpreter and you do not need to

compile your program before executing it

Python prompt and interact with the

 Object-oriented: Python supports style or

technique of programming that

encapsulates code within Objects

beginner programmers

Python Basic Syntax

Python Basic Syntax

 Interactive mode programming

 Open IDLE (Python GUI)

Python Basic Syntax

Python Basic Syntax

 Interactive mode programming

 Write the following

 Write the following

print “Hello; Python!”

Python Basic Syntax

Python Basic Syntax

 Script mode programming

 Open new window

 Open new window

Python Basic Syntax

Python Basic Syntax

 Script mode programming

 Write the following

 Write the following

print “Hello, Python!”

Python Basic Syntax

Python Basic Syntax

 Script mode programming

 Save as “Hello Python py”

 Save as “Hello Python.py”

 Run module

 No punctuation characters such as @,$,%

Python Identifiers

Python Identifiers

 Python is case sensitive (name and Name)

 Convention for Python

 Class names start with an uppercase letter

 Starting an identifier with a single leading

 Starting an identifier with a single leading

underscore “_” indicates that the identifier is

private

 Starting an identifier with two leading underscores

“ ”indicates a strongly private identifier

 If the identifier also ends with two trailing

 If the identifier also ends with two trailing

underscores, the identifier is a language-defined

special name

Lines and Indentation

Lines and Indentation

 Blocks of code for class and function

definitions or flow control denoted by line

definitions or flow control denoted by line

indentation

 No use of braces “{ }”

 No use of braces { }

 Test the following code

 Test the following code

Multi Line Statements

Multi-Line Statements

 Statements in Python typically end with a

new line

 Continuation on next line allowed with “\”

 Statements contained within [ ], { } and ( )

do not need to use the line continuation

character

Quotation in Python

Quotation in Python

 Python accepts single (‘), double (“) and

triple (‘’’ or “””) quotes to denote string

 The same types of quote should start and

end the string

 The triple quotes can be used to span the

Comments in Python

Comments in Python

 A hash sign “#” that is not inside a string

lateral begins a comment

 All characters after the # and up to the

physical line end are part of the comment

 A line can be commented by ALT+3 and

t d b ALT+4

Waiting for the User

Waiting for the User

 The following line of the program displays

the prompt “Press the enter key to exist.”

 The program will wait for the user to

press the Enter key

 Here “\n\n” are being used to create two

new lines before displaying the actual line

 This is a nice trick to keep a console

window open until the user is done with an

window open until the user is done with an

application

VARIABLES eBook for You

Standard Data Type

Standard Data Type

Assigning Values to Variables

Assigning Values to Variables

 Python variables do not have to be

explicitly declared

 The declaration happens automatically

when you assign a value to a variable

Numbers

 Python supports four different numerical

types

 int: signed integers

octal and hexadecimal)

 float: floating point real values

 complex: complex numbers

 Numbers with different base can be

represented

 Binary: start with 0B or 0b

 Octal: start with 0O or 0o

 Hexadecimal: start with 0x or 0X

>>>print str1*2 # Prints string two times

Hello World! Hello World!

>>> print str1 + "TEST" # Prints concatenated string

Hello World!TEST

Lists

 Most versatile of Python’s compound data

types

 A list contains items separated by

commas and enclosed within square

commas and enclosed within square

brackets “[ ]”

 All the items belonging to a list can be of

 All the items belonging to a list can be of

different data type

 The values stored in a list can be

 The values stored in a list can be

accessed using the slice operator “[ ]”

with indexes starting at 0 in the beginning

of the list

>>> print list1 [1:3] # Prints elements starting from 2 nd till 3 rd

>>> print list1 [1:3] # Prints elements starting from 2 nd till 3 rd

>>>print list1 + tinylist # Prints concatenated lists

>>>print list1 + tinylist # Prints concatenated lists

[ ‘abcd’, 786, 2.23, ‘john’, 70.2, 123, 'john‘]

Tuples

 A tuple is another sequence data type that

is similar to the list

 A tuple contains items separated by

commas and enclosed within parentheses

commas and enclosed within parentheses

“( )”

 The main difference between lists and

 The main difference between lists and

tuples is that the elements and the size of

the list can be changed while tuples

cannot be updated

Dictionaries

 Kind of hash table type

 Consist of key-value pairs

 A dictionary key can be almost any Python

type but are usually numbers or strings

 Values can be an arbitrary values

 Dictionaries are enclosed by curly braces

“{ }” and values can be accessed using

Dictionaries

 Example

>>> dict1 = { ‘name’: ‘john’ ‘code’: 6734 ‘dept’: ‘sales’ }

>>> print dict1 # Prints complete dictio nary

{'dept': 'sales', 'code': 6734, 'name': 'john'}

>>>print dict1[‘name’] # Prints value for ‘name’ key

>>>print dict1[ name ] # Prints value for name key

john

>>> print dict1.keys() # Prints all the keys

['dept' 'code' 'name']

>>>print dict1.values() # Prints all the values

['sales', 6734, 'john']

>>> dict2 = {}

>>> dict2[‘one’] = “This is one”

>>> dict2[2] = “This is two”

>>>print dict2[‘one’]

>>>print dict2[2]

CONTROL FLOW TOOLS eBook for You

Operators

 Python arithmetic operators

Operators

 Python arithmetic operators

Operators

 Python logical operators

a=True and b=True

Operators

 Python membership operators

Decision Making

Decision Making

 Decision making structures require that

the programmer specify one or more

the programmer specify one or more

conditions to be evaluated or tested by the

program

 If the condition is true, the program will

 Optionally, other statements may be

executed if the condition is false

 Python programming language assumes

any non-zero and non-null values as true

Decision Making

Decision Making

 IF statements

 Write the following code and test it

Decision Making

Decision Making

 IF…ELSE statements

 Write the following code and test it

Decision Making

Decision Making

 ELIF statements

 Write the following code and test it

Decision Making

Decision Making

 Nested IF statements

 Write the following code and test it

Loops

 Needed when a block of statements needs

to be executed several times

Loops

 While loop statements

 Block repeatedly executed as long as the given

 Block repeatedly executed as long as the given

condition is true

Loops

 For loop statements

 Block repeatedly executed for a defined number

 Block repeatedly executed for a defined number

of times

Loops

 Break statements

 Terminates the current loop and resumes

 Terminates the current loop and resumes

execution at the next statement

Loops

 Continue statements

 Returns the control to the beginning of the while

 Returns the control to the beginning of the while

loop

BUILT-IN FUNCTIONS AND

BUILT-IN FUNCTIONS AND

METHODS

Number Functions

Number Functions

 Mathematical functions (import math)

Number Functions

Number Functions

 Trigonometric functions (import math)

 Mathematical constants (import math)

String Functions and Methods

String Functions and Methods

String Functions and Methods

String Functions and Methods

String Functions and Methods

String Functions and Methods

String Functions and Methods

String Functions and Methods

List Functions

List Functions

List Methods

List Methods

USER-DEFINED FUNCTIONS eBook for You

Definition

 A function is a block of organized,

reusable code that is used to perform a

reusable code that is used to perform a

single, related action

 Functions provide better modularity and a

 Functions provide better modularity and a

high degree of code reusing

 Python gives many built-in functions like

 Python gives many built in functions like

print()

 Programmers can create their own

 Programmers can create their own

functions

Defining a Function

Defining a Function

 Simple rules to define a function

 Function blocks begin with the keyword def

followed by the function name and parentheses

“()”

 Any input parameters or arguments should be

placed within these parentheses

 The first statement of a function can be an

optional statement – the documentation string or

docstring

 The code block within every functions starts with a

colon “:” and is indented

Defining a Function

Defining a Function

 Example

 Simplest form of a Python function

Calling a Function

Calling a Function

 Once the basic structure of a function is

finalized you can execute it by calling it

finalized, you can execute it by calling it

from another function or from the Python

prompt

Pass by Reference

Pass by Reference

 All parameters are passed by reference

Function Arguments

Function Arguments

 You can call a function by using the

following types of formal arguments

Function Arguments

Function Arguments

 Required arguments

 Arguments passed to a function in the correct

 Arguments passed to a function in the correct

order

Function Arguments

Function Arguments

 Keyword arguments

 When you use keyword arguments in a function

 When you use keyword arguments in a function

call, the caller identifies the arguments by the

parameter name

Function Arguments

Function Arguments

 Default arguments

 Argument that assumes a default value if a value

 Argument that assumes a default value if a value

is not provided in the function call

Function Arguments

Function Arguments

 Variable-length arguments

 You may need to process a function for more

 You may need to process a function for more

arguments than you specified while defining the

function

Function Arguments

Function Arguments

 Return statement

 The return statement exists a function optionally

 The return statement exists a function, optionally

passing back an expression

FILES AND DIRECTORIES eBook for You

Reading Keyboard Input

Reading Keyboard Input

 Python provides two built-in functions to

read a line of text from standard input

read a line of text from standard input

which by default comes from the keyboard

 raw_input

 input

Reading Keyboard Input

Reading Keyboard Input

 The raw_input function

 This function reads one line from standard input

and returns it as a string

 It removes the trailing newline

Reading Keyboard Input

Reading Keyboard Input

 The input function

Opening and Closing Files

Opening and Closing Files

 The open function

 Before you can read or write a file, you have to

open it using Python’s built-in open() function

 S t

 Syntax

 file name: string value that contains the name of

 file_name: string value that contains the name of

the file that you want to access

 access_mode: determines the mode in which the

file has to be opened

Opening and Closing Files

Opening and Closing Files

 The open function

 The access_mode

Opening and Closing Files

Opening and Closing Files

 The file object attributes

 Once a file is opened and you have one file object

you can get various information related to that file

The Module OS

The Module OS

 Python “os” module provides methods

that help you perform file-processing

operations, such as renaming and deleting

fil

files

 Renaming and deleting files

 rename(): takes two arguments, the current

filename and the new filename

 remove(): to delete files by supplying the name of

 remove(): to delete files by supplying the name of

the file to be deleted as the argument

 chdir(): to change the current directory

 getcwd(): to display the current directory

 rmdir(): to delete the directory Before removing a

 rmdir(): to delete the directory Before removing a

directory, all the contents in it should be removed

QUESTIONS?

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