Python_Unit1_Introduction.pptx

UNIT I – Part 1
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UNIT 1

Python - Introduction
- widely used general-purpose, high level
programming language
- Python Programming was created by Dutch
Programmer, and released in
1991.
- Further developed by the Python Software
Foundation
- emphasises on code readability, and syntax
- allows programmers to express their concepts in
fewer lines of code.
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Guido van Rossum,

Why is Python called Python?
- Guido van Rossum named it after the television
comedy show Monty Python's Flying Circus
- between 1969 and 1974, which is still well-known
and watched around the world.
- Many Python examples and tutorials include jokes
from the show.
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History of Python
- Python laid its foundation in the late 1980s.
- The implementation of Python was started in
December 1989 by Guido Van Rossum at CWI
(Centrum Wiskunde & Informatica )in Netherland.
- In February 1991, Guido Van Rossum published
the code (labeled version 0.9.0)
- In 1994, Python 1.0 was released with new features
like lambda, map, filter, and reduce.
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UNIT 1

History of Python (Continued)
- Python 2.0 added new features such as list
comprehensions, garbage collection systems.
- On December 3, 2008, Python 3.0 (also called
"Py3K") was released. It was designed to rectify the
fundamental flaw of the language.
- ABC programming language is said to be the
predecessor of Python language, which was capable
of Exception Handling and interfacing with the
Amoeba Operating System.
- The following programming languages influence
Python:
– ABC language.
– Modula-3
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Python – Version List
Version Released Date
Python 1.0 January 1994
Python 1.5 December 31, 1997
Python 1.6 September 5, 2000
Python 2.0 October 16, 2000
Python 2.1 April 17, 2001
Python 2.3 July 29, 2003
Python 2.4 November 30, 2004
Python 2.7 July 3, 2010
Version Released Date
Python 3.1 June 27, 2009
Python 3.2 February 20, 2011
Python 3.4 March 16, 2014
Python 3.7 June 27, 2018
Python 3.9.6 June 28, 2021
Python 3.10.2 January 10,2022
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Features of Python
1) Easy to Learn and Use
- Its syntax is straightforward and same as the
English language.
- There is no use of the semicolon or curly-bracket,
the indentation defines the code block.
2) Expressive Language
- can perform complex tasks using a few lines of
code.
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Features of Python (Continued)
3) Interpreted Language
- is an interpreted language;(i.e) the Python program
is executed one line at a time which makes
debugging easy
4) Cross-platform Language
- can run equally on different platforms such as
Windows, Linux, UNIX, and Macintosh, etc by
writing a program only once.
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5) Free and Open Source
- It is freely available on its official
website www.python.org.
- "Anyone can download its source code without
paying any penny."
6) Object-Oriented Language
- Python supports object-oriented language and
concepts of classes and objects come into existence.
- supports inheritance, polymorphism, and
encapsulation, etc.
- helps to write reusable code and develop applications
in less code.
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7) Extensible
- implies that other languages such as C/C++ can be
used to compile the code and thus it can be used
further in our Python code.
- converts the program into byte code, and any
platform can use that byte code.
8) Large Standard Library
- provides a vast range of libraries for the various
fields such as machine learning, web developer, and
also for the scripting.
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9) GUI Programming Support
- Graphical User Interface is used for the developing
Desktop application.
10. Dynamic Memory Allocation
- need not specify the data-type of the variable.
- When value is assigned to a variable, it automatically
allocates the memory to the variable at run time. Suppose
integer value 15 is assigned to x , no need to write int x =
15. Just write x = 15.
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UNIT 1

Writing and Executing First Python
Python can be installed using Python Console.
www.python.org.
Python console can be used in several ways:
Two ways mentioned:
1. Using Command line and running interpreter directly
2. GUI software comes with installed python called as
Python’s Integrated Development and Learning
Environment (IDLE)
- Running the IDLE gives a prompt window of three
right rows
- Instructions are typed at the prompt and press ENTER
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The >>> symbol denotes the Python Prompt
- Python IDLE works on different platforms (windows,
Unix , MacOS)
- IDLE contains:
• Shell window,
• interactive interpreter,
• debugger,
• multi-window text editor (features like colorizing,
smart indent, call tips and auto completion)
- REPL editors can also be used.
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UNIT 1
(Read,Evaluate, Print, Loop)

Standard way to save & run a python program:
Step 1: Open an Editor.
Step 2: Write the instructions
Step 3: Save it as a file with the filename having the
extension .py
Step 4: Run the interpreter using python
program_name.py or using IDLE can run
Execute the program in python shell , press F5 (click
RUN menu & select RUN Module)
Exit from IDLE: File-> Exit or ctrl+Q or type quit() at
command prompt
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First Python Program
To print a message:
print (“Hello”)
To add two integers:
print (2 + 3)
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Literal Constants - NUMBERS
Literal Constants:
Literal – means literally .
- Value of literal constant can be used in programs
directly Eg: 7, 3.9,’A’,”Hello” - value cannot be
changed.
Numbers:
Refers to numeric value.
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COMPLEX NUMBERS
-3+7i
INTEGER eg: 5,7
LONG INTEGERS eg:
53546788999L
FLOATING POINT
3.23, 91.5E-2
NUMBER
- Commas are not used in numeric literals or
numeric values
- Floating point range 16 to 17 digits

Issues in dealing with floating point numbers:
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Arithmetic
overflow problem
Loss of Precision
Arithmetic
underflow
problem
- Multiply two very
large floating point
numbers is called as
arithmetic overflow.
- It is called as infinity.
- Division of two
floating numbers
resulting in small
magnitiude is called as
arithmetic underflow.
- Loss of precision
repeated infinitely
- Eg:1/3 = .333333

Built-in format()
- Any floating-point value may contain an arbitrary
number of decimal places hence should use built-
in format().
- float(16/float(3))) 5.3333333333333
- float(16/float(3))), ‘.2f’) 5.3
- format(3**50,’.5e’) 7.17898e+23
- format(123456, ‘,’) 123,456
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Simple Operations on Numbers
- Python carry out simple operations on numbers and type the operations
to be performed on to python console.
Eg: 50 + 40 – 35 55
- Division by Zero
Generates an error & no output is produced.
Eg:
Python 3.11.1 (tags/v3.11.1:a7a450f, Dec 6 2022, 19:58:39) [MSC v.1934
64 bit (AMD64)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> 15/0
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
ZeroDivisionError: division by zero
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- Dividing two integers:
if any two integer values are divided it produce a
floating point number.
- Python automatically converts integer to float called
as implicit conversion (type coercion).
Example:
>>> 5*3.0
15.0
>>> 19+3.5
22.5
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- Quotient and Remainder:
To find the quotient of two numbers floor division(//) is used.
To find the remainder of two numbers division modulo operator(%)
is used.
Exponentiation:
Python also supports ** operator.
Eg:
22.5
>>> 5**3
125
>>> 121**0.5
11.0
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Literal Constants - STRINGS
A STRING is a group of characters.
- Using Single Quotes(‘)
- Using Double Quotes(“)
- Using Triple Quotes(‘’ ‘ ‘’ ‘) – multi-line strings
Eg;
''' Good Morning everyone
... "welcome to CSDA'python'."happy reading'''
' Good Morning everyonen"welcome to
CSDA'python'."happy reading'
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Escape Sequences:
Eg:>>> print('what's your name?')
File "<stdin>", line 1
print('what's your name?')
^^^^^^^
SyntaxError: invalid syntax. Perhaps you forgot a
comma?
>>> print('What's your name?')
What's your name?
>>>
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Escape
Sequences
Purpose Example Output
Print Backslash Print(“”)
’ Print single-quote Print(“’”) ‘
” Print double-quote Print(“” ”) “
a Ring bell Print(“a”) Bell rings
f Print form feed
character
Print(“Hellof
World”)
Hello World
n Prints newline
character
Print(“Hellon
world”)
Hello World
t Prints a tab Print(“Hellot
World”)
Hello World
o Print octal values Print(“o56”) .
x Print hex values Print(“x87”) +
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Raw Strings:
A string that should display exactly as specified is
called as raw string.
It is specified by prefixing r or R to the string.
Example:
>>> print(R"what 's ur name")
what 's ur name
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String Formatting:
To format the floating point number built-in format
function is used.
Syntax:
Format(value, format_specifier)
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Value or the string Combination of
formatting options

Example
>>> format ('hello', '<30')
'hello '
>>> format ('hello','>30')
' hello'
>>> format("hello", "^30")
' hello '
>>>print("hello",format('-','-<10'),"world")
hello ---------- world
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Variables
- A Python variable is a reserved memory location to
store values.
- In other words, a variable in python program gives
data to the computer for processing.
- Its value can be varied.
- A Python identifier is a name used to identify a
variable, function, class, module or other object.
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Identifiers
-
Rules for Python identifiers:
- An identifier starts with a letter A to Z or a to z or an
underscore ( _ ) followed by zero or more letters,
underscores and digits (0 to 9).
- Python does not allow punctuation characters such as @,
$, and % within identifiers.
- Python is a case sensitive programming language.
Thus, Manpower and manpower are two different
identifiers in Python.
- Eg: valid identifier:sum, _my_var, num1, r , var_20, First
- Invalid indentifier: 1num, my-var, %check, Basic Sal 29
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Identifiers (Continued)
Here are naming conventions for Python identifiers :
- Class names start with an uppercase letter. All other
identifiers start with a lowercase letter.
Srcas is Valid and SRCAS is not valid
- 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 underscores,
the identifier is a language-defined special name.
- Reserved key words cannot be an identifier
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Data Types
- Variables can hold values of different types called as
datatypes.
- Different datatypes is required to store different types
of values in the variables.
- Divided into two categories
Immutable Data Types:
(i) Numeric, (ii) String (iii) Tuple
Mutable Data Types:
(i) List, (ii) Dictionary (iii) Set
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UNIT 1

Data Types (Continued)
1) Numeric
A numeric value is any representation of data
which has a numeric value. Python identifies three
types of numbers:
(a) Integer: Positive or negative whole numbers
(without a fractional part)
(b) Float: Any real number with a floating point
representation in which a fractional component is
denoted by a decimal symbol or scientific notation
(c) Complex number: A number with a real and
imaginary component represented as x+yj.
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2) String
- String literals in python are surrounded by either
single quotation marks, or double quotation marks.
'hello' is the same as "hello".
3) List
- collection which is ordered and changeable.
Allows duplicate members.
Example:
fruit = [“apple”, “Banana”, “Orange”]
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4) Tuple:
- collection which is ordered and unchangeable.
Allows duplicate members.
Example:
fruit = (“apple”, “Banana”, “Orange”)
5) Dictionary:
- collection which is unordered, changeable and
indexed, and they have keys and values.
Example:
Student = {“name”: “Raju”, “Age”:18,
“city”:”Kovai”}
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6) Set
- collection which is unordered and unindexed.
Example:
fruit = {“apple”, “Banana”, “Orange”}
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Data Types –Assigning or
initializing values to variable
- Python need not require explicitly to declare variables
to reserve memory space.
- Declaration done automatically when a value is
assigned with =.
- LHS of operand is the name of the variable;
- RHS of operand is the value stored in that variable.
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In python reassigning variables can be done as many times.
• Output:
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Python IDLE remembers variable names and values.
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MULTIPLE ASSIGNMENT
- Python allows programmers to assign a single value
to more than one variables simultaneously
Eg; sum=flag=b=a=0
- Different values to multiple variables simultaneously
Eg; sum, a, b, mesg=0,3,5, “result”
Note: Referencing a variable that has not assigned any
value result to error.
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UNIT 1

MULTIPLE ASSIGNMENT
str="hello"
num=10
print(str)
hello
print(age)
Traceback (most recent call
last):
File "<pyshell#3>", line 1, in
<module>
print(age)
NameError: name 'age' is not
defined
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str="hello"
num=10
age=10
print(str)
hello
print(num)
10
print(age)
10
del num
print(num)
Traceback (most recent call last):
File "<pyshell#12>", line 1, in <module>
print(num)
NameError: name 'num' is not defined.
Did you mean: 'sum'?
UNIT 1

MULTIPLE ASSIGNMENT
Program code two types:
Physical line –
what we see while writing the program
Logical line –
what python sees as a single statement
- More than one statement in a single line
semicolon should be used ;
Eg: all the below syntax are same
med="hello"; med="hello" med="hello“;
print(med); print(med) print(med)
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Boolean
- Another datatype in python
- It can contain two values TRUE or FALSE.
- It is created while assigning a value or with
relational operator.
- It is also created by comparing values using the
== operator.
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Boolean - Examples
boolean_var= True
print(boolean_var)
True
20!= 20
False
90<=90
True
87<87.0
False
20==30
False
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"python"!="python3.4"
True
87==87.0
True
87>=87.0
True
"PYTHON"=="PYTHON"
True
30> 50
False
UNIT 1

Input Operation
Python is interactive: To get input or information
from the user.
input() function is used.
- Prompts the user to provide some information,
process and the provide the result.
- This function takes user’s input as a string
Hence a number is taken as input it treats as
string only
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UNIT 1

Input Operation
Program:
name=input("What's your name?")
age=input("Enter your age")
print(name +",you are" + age + years old")
Output:
What's your
name?vidhya
Enter your
age39
vidhya,you
are39years
old
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Older versions used raw_input() as input function
UNIT 1

Comments
- Comments are non-executable statements in a program.
- They are added to describe the statements in the
program code.
- Comments make the program easily readable &
understandable .
- Interpreter simply ignore the comments.
- # indicate the comment line.
Example:
# this is a comment
Print(“hello”) # to display
# program ends here
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Reserved Keywords
- Reserved words (also called keywords) are
defined with predefined meaning and syntax in
the language.
- Reserved words can’t be used as
identifiers like
name of variable,
function etc.
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UNIT 1
and except lambda with
as finally nonlocal while
assert false none yield
break for not
class from or
continue global pass
def if raise
del import return
elif in true
else is TRY

Indentation
- White space at the beginning of the line is called
as Indentation.
- White space or the indentation is important.
- In python indentation is used to associate and
group statements.
- EXAMPLE
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UNIT 1

Indentation
- The level of indentation groups
statements to form a block of
statements
- In a block same indentation level to be
maintained for that group of
statements.
- Indent not correct is denoted by ^.
- Indent in python does not use {….}
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UNIT 1

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