Python programming language introduction unit

Python Programming
UNIT I
Introduction: History of Python,
Need of Python Programming, Applications,
Basics of PythonProgramming Using the REPL(Shell),
Running Python Scripts, Variables,
Assignment, Keywords, Input-Output,Indentation.

python
•Python was developed by Guido van
Rossum in the late eighties and early
nineties at the National Research Institute
for Mathematics and Computer Science in
the Netherlands
•Python is derived from many other
languages, including ABC, Modula-3,
C, C++, Algol-68, SmallTalk, Unix shell,
and other scripting languages
•At the time when he began implementing Python, Guido van Rossum was
also reading the published scripts from "Monty Python's Flying Circus" (a
BBC comedy series from the seventies, in the unlikely case you didn't know).
It occurred to him that he needed a name that was short, unique, and
slightly mysterious, so he decided to call the language Python.

Python
• Python is a high-level, interpreted, interactive
and object-oriented scripting language.
Python is designed to be highly readable

Need of Python Programming
• Easy-to-read: Python code is more clearly
defined and visible to the eyes.
• Easy-to-maintain: Python's source code is
fairly easy-to-maintain.

Interactive Mode: Python has support for an
interactive mode which allows interactive
testing and debugging of snippets of code.

Extendable
• You can add low-level
modules to the
Python interpreter.
• These modules enable
programmers to add
to or customize their
tools to be more
efficient.

• GUI Programming: Python supports GUI
applications that can be created and ported to
many system calls, libraries, and windows
systems, such as Windows MFC, Macintosh,
and the X Window system of UNIX.

• Scalable: Python provides a better structure
and support for large programs than shell
scripting.

• Software quality
Python code is designed to be
readable, and hence reusable
and maintainable— much more
so than traditional scripting
languages. The uniformity of
Python code makes it easy to
understand, even if you did not
write it.

Developer productivity
Python boosts developer productivity many
times beyond compiled or statically typed
languages such as C, C++, and Java.
Python code is typically one-third to less to debug, and less to maintain after the fact.
Python programs also run immediately, without the lengthy compile and link steps
required by some other tools

• Support libraries
Python comes with a large collection of prebuilt and
portable functionality, known as the standard
library. This library supports an array of application-
level programming tasks, from text pattern
matching to network scripting.

It's Object-Oriented
Python is an object-
oriented language, from
the ground up. Its class
model supports
advanced notions such
as polymorphism,
operator overloading,
and multiple inheritance

• It's Free
Python is freeware—Its open source software.
Download and use it.

• It's Portable
Python is written in portable ANSI C, and
compiles and runs on virtually every major
platform in use today. For example, it runs on
UNIX systems, Linux, MS-DOS, MS-Windows (95,
98, NT), Macintosh, Amiga, Be-OS, OS/2, VMS,
QNX, and more

• It's Powerful
From a features perspective, Python is
something of a hybrid. Its tool set places it
between traditional scripting languages (such as
Tcl, Scheme, and Perl), and systems languages
(such as C, C++, and Java).

Automatic memory management
Python automatically allocates
and reclaims ("garbage collects")
objects when no longer used, and
most grow and shrink on demand.

It's Easy to Use
simplicity make
programming more fun
than work.
To run a Python program, you simply type it
and run it. There are no intermediate
compile and link steps (as when using
languages such as C or C++).
It's Easy to Learn
Compared to other
programming languages,
the core Python
language is amazingly
easy to learn.

Internet Scripting
Python comes with standard Internet utility
modules that allow Python programs to
communicate over sockets, extract form
information sent to a server-side CGI script,
parse HTML, transfer files by FTP, process XML
files, and much more.

Database Programming
Python provides a simple object-persistence
system: it allows programs to easily save and
restore entire Python objects to files. For more
traditional database demands, there are Python
interfaces to Sybase, Oracle, Informix, ODBC, and
more.

• Image Processing, AI, Distributed Objects, Etc.
• Python is commonly applied in more domains
than can be mentioned here.
• For instance, image processing for Python is
implemented as a set of library components
implemented in a compiled language such as C,
along with a Python frontend layer on top used to
configure and launch the compiled components.
• Machine Learning,AI,IOT….

Who Uses Python Today?
• Google makes extensive use of Python in its web search systems.
• The popular YouTube video sharing service is largely written in
Python.
• The Raspberry Pi single-board computer promotes Python as its
educational language.
• The widespread BitTorrent peer-to-peer file sharing system began
its life as a Python program.
• Google‘s App Engine web development framework uses Python as
an application language.
• Maya, a powerful integrated 3D modeling and animation system,
provides a Python scripting API.
• Intel, Cisco, Hewlett-Packard, Seagate, Qualcomm, and IBM use
Python for hardware testing.
• NASA, Los Alamos, Fermilab, JPL, and others use Python for
scientific programming tasks.
• And many more……………….

The Python Virtual Machine:
• Once your program has been compiled to byte
code (or the byte code has been loaded from
existing .pyc file), it is shipped off for
execution to something generally known as
the python virtual machine (PVM).

Applications of Python:
• Systems Programming
• GUIs
• Internet Scripting
• Database Programming
• Rapid Prototyping
• Numeric and Scientific
Programming
• …………

Python’s Technical Strengths?
• It‘s Object-Oriented and Functional
• It‘s Free
• It‘s Portable
• It‘s Powerful
• It‘s Mixable
• It‘s Relatively Easy to Use
• It‘s Relatively Easy to Learn

Installation in ubuntu
• commands:
1)cd /usr/src sudo wget
2)https://www.python.org/ftp/python/3.7.3/Py
thon-3.7.3.tgz
3)sudo tar xzf Python-3.7.3.tgz
4)cd Python-3.7.3

Running Python:
Running Python Interpreter:
Python comes with an interactive interpreter.
When you type python in your shell or
command prompt, the python interpreter
becomes active with a >>> prompt and waits
for your commands.

Running Python:
Running Python Scripts in IDLE:
•Goto File menu click on New File (CTRL+N) and write the code
and save add.py a=input("Enter a value ")
b=input("Enter b value ") c=a+b
print "The sum is",c
•And run the program by pressing F5 or Run Run Module.

Running python scripts in Command Prompt:
Before going to run we have to check the PATH in
environment variables.
Open your text editor, type the following text and
save it as hello.py.
print "hello"
And run this program by calling python hello.py. Make
sure you change to the directory where you saved
the file before doing it.
Running Python:

Variables
Variables in a computer program
are similar to buckets
where information can be maintained

Python Variables
• Variables are nothing but reserved memory
locations to store values. when you create a
variable you reserve some space in memory.
• Variables are containers for storing data values.
• Based on the data type of a variable, the
interpreter allocates memory and decides what
can be stored in the reserved memory. Therefore,
by assigning different data types to variables, you
can store integers, decimals or characters in these
variables

int x;
float y;
x=10
y=20.5
Variables
x=10
y=20.5
C/C++ python
x is automatically
treated as int because
10 is integer value
y is automatically
Treated as float
because 20.5 is
float value
x is
declared
as integer
y is
declared
as float
In Python,there is no need to declare a variable.A variable is created the moment
you first assign a value to it

Variable Names
• A variable can have a short name (like x and y) or a
more descriptive name (age, carname, total_volume).
Rules for Python variables:
• A variable name must start with a letter or the
underscore character
• A variable name cannot start with a number
• A variable name can only contain alpha-numeric
characters and underscores (A-z, 0-9, and _ )
• Variable names are case-sensitive (age, Age and AGE
are three different variables)

Assigning Values to Variables
• Python variables do not need explicit
declaration to reserve memory space. The
declaration happens automatically when you
assign a value to a variable. The equal sign (=)
is used to assign values to variables.
• The operand to the left of the = operator is
the name of the variable and the operand to
the right of the = operator is the value stored
in the variable.

Multiple Assignments to variables
• Python allows you to assign a single value to several
variables simultaneously.
• For example –
• a = b = c = 1
• Here, an integer object is created with the value 1, and all
three variables are assigned to the same memory location.
You can also assign multiple objects to multiple variables.
• For example –
• a, b, c = 1, 2.5, ”lakshman”
• Here, two integer objects with values 1 and 2 are assigned
to variables a and b respectively, and one string object with
the value “lakshman" is assigned to the variable c.

KEYWORDS
• The following list shows the Python keywords. These are reserved
words and you cannot use them as constant or variable or any
other identifier names. All the Python keywords contain lowercase
letters only.

INPUT Function
• To get input from the user you can use the
input function.
• When the input function is called the program
stops running the program, prompts the user
to enter something at the keyboard Python
provides the function input().
• input has an optional parameter, which is the
prompt string.

OUTPUT function:
We use the print() function or print keyword to output
data to the standard output device (screen). This
function prints the object/string written in function.
The actual syntax of the print() function is
print(*objects, sep=' ', end='n', file=sys.stdout,
flush=False)
Here, objects is the value(s) to be printed.
The sep separator is used between the values. It
defaults into a space character. After all values are
printed, end is printed. It defaults into a new line ( n ).

Indentation
• Like c or c++ ,there are no { , } in python.
• Python blocks are divided based on
indentation.
• A code block (body of a function, loop etc.) starts with indentation
and ends with the first unindented line. The amount of indentation
is up to you, but it must be consistent throughout that block.

Python programming language introduction unit

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