Introduction to Python Basics

2011 ANSYS, Inc. November 29, 20121

Python Basics


What is Python

Python Programming

Python console External to WB

Python Command Window in WB

Outline


Python is a object-oriented, interpreted, and interactive programming language

Python code is interpreted and portable between platforms

Python combines remarkable power with very clear syntax

It has modules, classes, exceptions, very high level dynamic data types, and dynamic typing

There are interfaces to many system calls and libraries

Python is also used as an extension language for applications written in other languages that need easy-to-use scripting or automation interfaces

IronPython is the Python Workbench uses IronPython is an implementation of the popular programming language Python for

.NET, by Microsoft

It brings new possibilities to .NET as well as Python programmers

It uses Python 2.6 on .NET 2.0

What is Python?


Free materials

http://www.python.org/ Python download all formats

Tutorial and documentation

http://ironpython.codeplex.com/ IronPython studio is free Microsoft SDK that allows you to manage your projects

and develop using native windows forms

http://www.tutorialspoint.com/python/index.htm Free book - http://greenteapress.com/thinkpython/thinkCSpy.pdf

Recommended books

Learning Python by Mark Lutz and David Ascher Python Pocket Reference by Mark Lutz IronPython in Action by Michael J.Ford and Christian Muirhead

For people wanting to use Iron python to take advantage of the .NET framework

ANSYS 14.5 Help Workbench Scripting Guide

Recommended References


Notepad++

Supports several languages (Python, Jscript, XML, )

IDLE

Standard Python editor that comes with Python. Good for most small programs.

SPE

Advanced non-commercial development environment

Erik

Powerful development environment that helps managing big projects with many files, as well as testing and debugging them

SharpDevelop

Development Environment for .NET (e.g IronPython based custom GUI)

Python Editors


You can install Python on your machine or use the IronPythonversion installed with ANSYS

Invoke the ipy.exe in command prompt to have a Python console

Path: C:\Program Files\ANSYS Inc\v145\commonfiles\IronPython\ipy.exe

Python console External to WB

You can also just drag and drop the ipy.exe file to a standard command prompt!


Overview:

You can use any Python command from the interactive Python command line:

Everything works in exactly the same way as it would in a program.

You can define code blocks by writing extra lines:

Tips: You can leave the command line by Ctrl-Z

(Windows) or Ctrl-D (Linux).

The CLI works great as a pocket calculator. Writing code blocks with 2+ lines in the CLI

gets painful quickly.

From IDLE, you can execute a program in the command line by pressing F5.

Python Command Line (CLI)


Essentials:

All program files should have the extension .py

Indentation is a central element of Python syntax, marking code blocks. Code blocks should be indented by spaces/tab.

Indentation must not be used for decorative purposes

Only one command per line is allowed

Python does not have:

Memory allocation

Declaration of variables and types

Writing Python Programs


Python Programming


A variable: Dont need to be pre declared

As Python scripts are run via an interpreter it will work out for itself the type of information and memory required

The name must start with an alphabetic character Can be any length

Variable Types: Numbers String List Tuple Dictionary

Python doesnt enforce variable types A variable can change type

Variables

Using a good editor helps a lot!


Colon Required at the end of compound statement headers (the first

line of an if, while, for, etc.)

Semicolon Don't terminate all of your statements with a semicolon(;) It is not required unless you're placing more than one

statement on a single line

Whitespace Important only for the indentation level (i.e. the whitespace at

the very left of your statements). Everywhere else, whitespace is not significant

Comments Syntax # 1: # Comment

Text after # is ignored in a single line Syntax # 2: Comment

Text between pairs is ignored

Case-sensitivity Python is case-sensitive Variable names may mix upper- and lower-case Calling code must match the case exactly Python keywords are case-sensitive too

Syntax


Arithmetic operators Add, subtract, multiply, division , modulus, exponent, Floor division

Assignment operators Simple assignment Multiple assignments to same value Compound assignment

Logical operators and, or, not

Relational operators Comparisons return Boolean values Equal to, not equal to Less than, greater than Less than or equal to, greater than or equal to

Membership operators To test for membership in a sequence, such as strings, lists, or tuples in, not in

Identity Operators To compare the memory locations of two objects is, is not

Operators


If-Else conditional

Variations if,

if...else,

elif,

nested if

Conditions Boolean or non-zero

String Comparison

Complex comparison

Flow Control

!

Indentation:The level of indentation determines the end of a conditionColon:Required at the end of compound statement headers


while loop

The while loop continues until the expression becomes false.

The expression has to be a logical expression and must return either a true or a false value

for loop

iterate over the items of any sequence, such as a list or a string

The first item in the sequence is assigned to the iterating variable

An alternative way of iterating through each item is by index

Flow Control (2)


break statement

terminates the current loop and resumes execution at the next statement

continue statement

returns the control to the beginning of the loop

else statement

executed when the loop has exhausted iterating the list (for loop)

is executed when the condition becomes false (while loop)

pass statement

used when a statement is required syntactically but you do not want any command or code to execute

Flow Control (3)


Function declaration begin with the keyword def followed by the function name and parentheses

Input parameters or arguments should be placed within these parentheses

Can have default arguments

The first statement of a function can be an optional statement

the documentation string of the function or docstring.

The code block within every function starts with a colon (:) and is indented.

The statement return [expression] exits a function, A return statement with no arguments is the same as

return None.

Functions


Python supports four different numerical types: int, float, long, complex

Change number explicitly from one type to another int(x) float(x)

Built-in Number Functions Mathematical Functions

abs(x), min(x1, x2, ..),

Trigonometric Functions Import math module to avail these

sin(x), acos(x),

Random Functions

Mathematical Constants Import math module to avail these pi, e

Numbers


Strings are stored as a list of single characters strings

Built-in String Methods len(string) join() split()

String Special Operators Concatenation (+) Range Slice [ : ] Suppress actual meaning of Escape

characters (r/R)

Membership (in, not in)

String and number concatenation Convert the number to string for

concatenation

Strings


Variables and strings can be combined, using formatting characters. This works also within a print statement. In both cases, the number of values and formatting characters must be equal.

s = 'Result: %i'%(number) print 'Hello %s!'%('Roger') print (%6.3f/%6.3f)%(a,b)

The formatting characters include: %i an integer. %4i an integer formatted to length 4. %6.2f a float number with length 6 and 2 after the comma. %10s a right-oriented string with length 10.

Escape characters Strings may contain also the symbols: \t (tabulator), \n (newline), \r (carriage return),

and \\ (backslash)

To read and use a staring containing special characters, use r before string

E.g. filePath = rE:\temp # w/o the r, it will be treated as E: *tab] emp

String Formatting


The list is a most versatile datatype available in Python

written as a list of comma-separated values (items) between square brackets.

Accessing Values in Lists use the square brackets for slicing along with the

index or

indices to obtain value available at that index

List modification Append elements Delete elements

Basic List Operations Lists respond to the + and * operators much like

strings

Built-in List Functions & Methods len(), max(), min(), sort(), reverse(), append(), remove(),

Lists


The Dictionary is a container type that can store any number of Python objects, including other container types

Dictionaries consist of pairs (called items) of keys and their corresponding values Also known as associative array or hash table

Syntax: Each key is separated from its value by a colon (:) Items are separated by commas whole thing is enclosed in curly braces

Accessing values Use square brackets along with the key to obtain its value Trying to access a data item with a key which is not part of the dictionary, gives error

Adding new entries Deleting entries

Properties of Dictionary Keys No duplicate keys allowed Can use strings, numbers, or tuples as dictionary keys

Built-in Dictionary Functions & Methods len(), str(), cmp(), dict.copy(), dict.items(), dict.values()

Dictionaries


An object: Is a complex variable that has:

Data (often called properties)

Functions (often called methods)

Is an instance of a class A class defines a category of objects

Syntax Python uses a dot notation

object . property

The dot connects the object to its properties and methods

No whitespace!

Property and method names are case-sensitive!

Properties:

A property is any valid variable type Methods:

Methods follow the same rules as functions

Classes and Objects

class: Person

property: name

property: age

name = Mary

age = 30

name = John

age = 55

name = Susan

age = 22

# Propertiesperson.name = MarynewPerson = person.childnewPerson.name = John

# Methodsperson.Talk()person.Relocate( New York )


The class statement creates a new class definition

The name of the class immediately follows the keyword class followed by a colon

The first method __init__() called class constructor or initialization method

Creating an instance objects:

call the class name and pass in whatever arguments its __init__ method accepts

self points to the new object Use self to define properties for your class

Defining a Class


A module is a file containing Python definitions and statements

A module can define functions, classes, and variables You can benefit from different modules by importing them to your code!

import Statement:

Imports a module It is customary but not required to place all import statements at the

beginning of the code

from...import Statement

imports specific attributes from a module into the code

fromimport * Statement

import all names from a module into the current namespace

Modules


Getting the current time and date:

The time module offers functions for getting the current time and date.

Finding out what is in a module

The contents of any module can be examined with:dir( name_of_module )

help( name_of_module )

Useful Python modules


Exceptions are the Python mechanism to make sure that code do not blow up in the wrong moment, so that important data is saved

Except, else and finally: Whenever the according kind of error occurs within a

try clause, the except code block will be executed. If no exception occurs, the else clause will be executed instead. After any of the two, the code block after finally is executed.

else and finally are required for building subtle cleanup operations after an error. In most situations, they are not necessary.

Typical Exceptions: ZeroDivisionError When dividing by zero. KeyError A key in a dictionary does not exist. ValueError A type conversion failed. IOError A file could not be opened.

Exceptions


Opening files for reading Text files can be accessed using the open() function. It returns an open file from which its

contents can be extracted as a string.

f = open('my_file.txt')

text = f.read()

Opening files for writing Writing text to files is very similar. The only difference is the 'w' parameter.f = open('my_file.txt','w')

f.write(text)

Appending to files It is possible to add text to an existing file, too.f = open('my_file.txt','a)

f.write(text)

Closing filesf.close()

File Operations


Writing directory names in Python

Replace the backslash '\' by a double backslash (because '\' is also used for '\n' and '\t')f = open('..\\my_file.txt')

f = open('C:\\python\\my_file.txt')

Managing file paths, directories etc.

With the os module, we can change to a different directory:import os

os.chdir(''..\\python'')

os.path.join(C:\Temp, abc.txt) # path = C:\Temp\abc.txt

To get a list with all files:os.listdir(''..\\python'')

Function to check whether a file exists:os.path.exists('my_file.txt')

File Operations (2)


Python Command Window in WB

1

2

3


Command Window supports:

Command completion Command history Keyboard shortcuts for cursor navigation and editing

Command Window


Project & Data Model Concepts


Project & Data Model Concepts (2)

System:A collection of components that together provide a workflow to achieve an engineering simulation goal.

Systems are created from System Templates.



Component:A collection of data and a data editor that work together to achieve a CAE-related task.

A Component is represented by a Cell in the Workbench Project Schematic.



Component Data Container: Data unique to an individual component, and the services to manage and manipulate it.



Data Entity:A data structure defined within a data container. A data container often has several data entities.


Try out

Record a journal from WB and using any text editor, extract the user inputs to the top

Replay the journal file

Introduction to Python Basics

Documents

Transcript of Introduction to Python Basics