UNIT II
DATA, EXPRESSIONS, STATEMENTS
Python interpreter and interactive mode; values and types: int, float, boolean, string, and list; variables,
expressions, statements, tuple assignment, precedence of operators, comments; Modules and functions,
function definition and use, flow of execution, parameters and arguments; Illustrative programs: exchange
the values of two variables, circulate the values of n variables, distance between two points.
1. INTRODUCTION TO PYTHON:
Python is a general-purpose interpreted, interactive, object-oriented, and high-level
programming language.
It was created by Guido van Rossum during 1985- 1990.
Python got its name from “Monty Python’s flying circus”. Python was released in the year 2000.
• Python is interpreted: Python is processed at runtime by the interpreter. You do not need to
compile your program before executing it.
• Python is Interactive: You can actually sit at a Python prompt and interact with the interpreter
directly to write your programs.
• Python is Object-Oriented: Python supports Object-Oriented style or technique of programming
that encapsulates code within objects.
• Python is a Beginner's Language: Python is a great language for the beginner-
Level programmers and supports the development of a wide range of applications.
Python Features:
• Easy-to-learn: Python is clearly defined and easily readable. The structure of the program is very
simple. It uses few keywords.
• Easy-to-maintain: Python's source code is fairly easy-to-maintain.
• Portable: Python can run on a wide variety of hardware platforms and has the same interface on all
platforms.
• Interpreted: Python is processed at runtime by the interpreter. So, there is no need to compile a
program before executing it. You can simply run the program.
• Extensible: Programmers can embed python within their C,C++,JavaScript
, ActiveX, etc.
• Free and Open Source: Anyone can freely distribute it, read the source code, and edit it.
• High Level Language: When writing programs, programmers concentrate on solutions of the
current problem, no need to worry about the low level details.
• Scalable: Python provides a better structure and support for large programs than shell scripting.
Applications:
Bit Torrent file sharing
Google search engine, YouTube
Intel, Cisco, HP,IBM
i–Robot
NASA
Face book, Drop box
31
,Python interpreter:
Interpreter: To execute a program in a high-level language by translating it one line ata time.
Compiler: To translate a program written in a high-level language into a low-level language all at once, in
preparation for later execution.
Compiler Interpreter
Compiler Takes Entire program as input Interpreter Takes Single instruction as input
No Intermediate is Object Code
Intermediate Object Code is Generated
Generated
Conditional Control Statements are Conditional Control Statements are
Executes faster Executes slower
Memory Requirement is More(Since Object Memory Requirement is Less
Code is Generated)
Program need not be compiled every time Every time higher level program is
converted into lower level program
Errors are displayed after entire program is checked Errors are displayed for every instruction
interpreted (if any)
Example : C Compiler Example : PYTHON
Modes of python interpreter:
Python Interpreter is a program that reads and executes Python code. It uses 2 modes of Execution.
1. Interactive mode
2. Script mode
Interactive mode:
Interactive Mode, as the name suggests, allows us to interact with OS.
When we type Python statement, interpreter displays the result(s) immediately.
Advantages:
Python, in interactive mode, is good enough to learn, experiment or explore.
Working in interactive mode is convenient for beginners and for testing small pieces of code.
Drawback:
We cannot save the statements and have to retype all the statements once again to re-run them.
In interactive mode, you type Python programs and the interpreter displays the result:
>>> 1 + 1
2
The chevron, >>>, is the prompt the interpreter uses to indicate that it is ready for you to enter code. If you
type 1 + 1, the interpreter replies 2.
>>> print ('Hello, World!')
Hello, World!
32
,This is an example of a print statement. It displays a result on the screen. In this case, the result is the words.
Script mode:
In script mode, we type python program in a file and then use interpreter to execute the content of the
file.
Scripts can be saved to disk for future use. Python scripts have the
extension .py, meaning that the filename ends with.py
Save the code with filename.py and run the interpreter in script mode to execute the script.
Interactive mode Script mode
A way of using the Python interpreter by A way of using the Python interpreter to read and
typing commands and expressions at the prompt. execute statements in a script.
Can’t save and edit the code Can save and edit the code
If we want to experiment with the code, If we are very clear about the code, we can
we can use interactive mode. use script mode.
we cannot save the statements for further use and we we can save the statements for further use and we no
have to retype all the statements to re-run them. need to retype all the statements to re-run them.
We can see the results immediately. We can’t see the code immediately.
Integrated Development Learning Environment(IDLE):
Is a graphical user interface which is completely written in Python.
It is bundled with the default implementation of the python language and also comes with optional
part of the Python packaging.
Features of IDLE:
Multi-window text editor with syntax highlighting.
33
, Auto completion with smart indentation.
Python shell to display output with syntax highlighting.
2.VALUES AND DATATYPES
Value:
Value can be any letter, number or string.
Eg, Values are 2, 42.0, and 'Hello, World!'. (These values belong to different datatypes.)
Data type:
Every value in Python has a data type.
It is a set of values, and the allowable operations on those values.
Python has four standard data types:
Numbers:
Number data type stores Numerical Values.
This data type is immutable [i.e. values/items cannot be changed].
Python supports integers, floating point numbers and complex numbers. They are defined as,
Sequence:
A sequence is an ordered collection of items, indexed by positive integers.
It is a combination of mutable (value can be changed) and immutable (values cannot be changed)
datatypes.
34
DATA, EXPRESSIONS, STATEMENTS
Python interpreter and interactive mode; values and types: int, float, boolean, string, and list; variables,
expressions, statements, tuple assignment, precedence of operators, comments; Modules and functions,
function definition and use, flow of execution, parameters and arguments; Illustrative programs: exchange
the values of two variables, circulate the values of n variables, distance between two points.
1. INTRODUCTION TO PYTHON:
Python is a general-purpose interpreted, interactive, object-oriented, and high-level
programming language.
It was created by Guido van Rossum during 1985- 1990.
Python got its name from “Monty Python’s flying circus”. Python was released in the year 2000.
• Python is interpreted: Python is processed at runtime by the interpreter. You do not need to
compile your program before executing it.
• Python is Interactive: You can actually sit at a Python prompt and interact with the interpreter
directly to write your programs.
• Python is Object-Oriented: Python supports Object-Oriented style or technique of programming
that encapsulates code within objects.
• Python is a Beginner's Language: Python is a great language for the beginner-
Level programmers and supports the development of a wide range of applications.
Python Features:
• Easy-to-learn: Python is clearly defined and easily readable. The structure of the program is very
simple. It uses few keywords.
• Easy-to-maintain: Python's source code is fairly easy-to-maintain.
• Portable: Python can run on a wide variety of hardware platforms and has the same interface on all
platforms.
• Interpreted: Python is processed at runtime by the interpreter. So, there is no need to compile a
program before executing it. You can simply run the program.
• Extensible: Programmers can embed python within their C,C++,JavaScript
, ActiveX, etc.
• Free and Open Source: Anyone can freely distribute it, read the source code, and edit it.
• High Level Language: When writing programs, programmers concentrate on solutions of the
current problem, no need to worry about the low level details.
• Scalable: Python provides a better structure and support for large programs than shell scripting.
Applications:
Bit Torrent file sharing
Google search engine, YouTube
Intel, Cisco, HP,IBM
i–Robot
NASA
Face book, Drop box
31
,Python interpreter:
Interpreter: To execute a program in a high-level language by translating it one line ata time.
Compiler: To translate a program written in a high-level language into a low-level language all at once, in
preparation for later execution.
Compiler Interpreter
Compiler Takes Entire program as input Interpreter Takes Single instruction as input
No Intermediate is Object Code
Intermediate Object Code is Generated
Generated
Conditional Control Statements are Conditional Control Statements are
Executes faster Executes slower
Memory Requirement is More(Since Object Memory Requirement is Less
Code is Generated)
Program need not be compiled every time Every time higher level program is
converted into lower level program
Errors are displayed after entire program is checked Errors are displayed for every instruction
interpreted (if any)
Example : C Compiler Example : PYTHON
Modes of python interpreter:
Python Interpreter is a program that reads and executes Python code. It uses 2 modes of Execution.
1. Interactive mode
2. Script mode
Interactive mode:
Interactive Mode, as the name suggests, allows us to interact with OS.
When we type Python statement, interpreter displays the result(s) immediately.
Advantages:
Python, in interactive mode, is good enough to learn, experiment or explore.
Working in interactive mode is convenient for beginners and for testing small pieces of code.
Drawback:
We cannot save the statements and have to retype all the statements once again to re-run them.
In interactive mode, you type Python programs and the interpreter displays the result:
>>> 1 + 1
2
The chevron, >>>, is the prompt the interpreter uses to indicate that it is ready for you to enter code. If you
type 1 + 1, the interpreter replies 2.
>>> print ('Hello, World!')
Hello, World!
32
,This is an example of a print statement. It displays a result on the screen. In this case, the result is the words.
Script mode:
In script mode, we type python program in a file and then use interpreter to execute the content of the
file.
Scripts can be saved to disk for future use. Python scripts have the
extension .py, meaning that the filename ends with.py
Save the code with filename.py and run the interpreter in script mode to execute the script.
Interactive mode Script mode
A way of using the Python interpreter by A way of using the Python interpreter to read and
typing commands and expressions at the prompt. execute statements in a script.
Can’t save and edit the code Can save and edit the code
If we want to experiment with the code, If we are very clear about the code, we can
we can use interactive mode. use script mode.
we cannot save the statements for further use and we we can save the statements for further use and we no
have to retype all the statements to re-run them. need to retype all the statements to re-run them.
We can see the results immediately. We can’t see the code immediately.
Integrated Development Learning Environment(IDLE):
Is a graphical user interface which is completely written in Python.
It is bundled with the default implementation of the python language and also comes with optional
part of the Python packaging.
Features of IDLE:
Multi-window text editor with syntax highlighting.
33
, Auto completion with smart indentation.
Python shell to display output with syntax highlighting.
2.VALUES AND DATATYPES
Value:
Value can be any letter, number or string.
Eg, Values are 2, 42.0, and 'Hello, World!'. (These values belong to different datatypes.)
Data type:
Every value in Python has a data type.
It is a set of values, and the allowable operations on those values.
Python has four standard data types:
Numbers:
Number data type stores Numerical Values.
This data type is immutable [i.e. values/items cannot be changed].
Python supports integers, floating point numbers and complex numbers. They are defined as,
Sequence:
A sequence is an ordered collection of items, indexed by positive integers.
It is a combination of mutable (value can be changed) and immutable (values cannot be changed)
datatypes.
34
