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UNIT 02: BASICS OF PYTHON
PROGRAMMING
Introduction-Python Interpreter-Interactive and
script mode -Values and types, variables,
operators, expressions, statements, precedence
of operators, Multiple assignments, comments,
input function, print function, Formatting
numbers and strings, implicit/explicit type
conversion.

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 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++,Java
script ,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.

Python Interpreter
• A python interpreter is a computer program that converts each
high-level program statement into machine code.
• Translating it one line at a time
• Compiler: To translate a program written in a high-level language
into a low-level language all at once

Difference between Interpreter and
Compiler
Compilers Interpreters
Compilers translate the entire source code into
machine code before execution.
Interpreters translate and execute the source
code line by line.
Compiled code runs faster because it's already
translated into machine code.
Interpreted code runs slower because it must be
translated on the fly.
Compilers generate an executable file that can
be run independently.
Interpreters require the source code to be
present at runtime.
Compilers display all errors at once after
compilation.
Interpreters display errors one at a time during
execution.
Compiled languages include C, C++, and Java. Interpreted languages include Python, Ruby, and
JavaScript.
Compilers have a longer development cycle due
to the compilation step.
Interpreters have a shorter development cycle as
code can be tested immediately.
Compiled code is platform-dependent. Interpreted code is platform-independent.

MODES OF PYTHON INTERPRETER
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

Python unit 2 is added. Has python related programming content

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.

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.
• Auto completion with smart indentation.
• Python shell to display output with syntax highlighting.

Values and types
Value: Value can be any letter ,number or string.
Eg, Values are 2, 42.0, and 'Hello, World!'. (These values belong to
different data types.)
Data type: Every value in Python has a data type. It is a set of values,
and the allowable operations on those values.

Numeric Data Types
type() function is used to determine the type of Python data type.
• Integers – This value is represented by int class. It contains positive or
negative whole numbers (without fractions or decimals). In Python,
there is no limit to how long an integer value can be.
• Float – This value is represented by the float class. It is a real number
with a floating-point representation. It is specified by a decimal point.
Optionally, the character e or E followed by a positive or negative
integer may be appended to specify scientific notation.
• Complex Numbers – A complex number is represented by a complex
class. It is specified as (real part) + (imaginary part)j . For example – 2+3j

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) data types.
1.Strings (Immutable)
2. Lists( mutable)
3. Tuples(Immutable)

Strings
• A String in Python consists of a sequence of characters - letters, numbers, and special
characters.
• Strings are marked by quotes:
• single quotes (' ') Eg, 'This a string in single quotes'
• double quotes (" ") Eg, "'This a string in double quotes'"
• triple quotes(""" """) Eg, This is a paragraph. It is made up of multiple lines and
sentences.""“
• Individual character in a string is accessed using a subscript (index).
• Characters can be accessed using indexing and slicing operations.
• Strings are immutable i.e. the contents of the string cannot be changed after it is
created.

Indexing
String A H E L L 0
Positive Index 0 1 2 3 4
Negative Index -5 -4 -3 -2 -1
Example: A[0] or A[-5] will display “H”
Example: A[1] or A[-4] will display “E”
Str=‘Python Program’
Str[-3]
Str[3]
Str[6]
Str[7]

Operations on string
• Indexing
• Slicing
• Concatenation
• Repetitions
• Member ship

Indexing Accessing the item in the position
Slicing Slice operator is used to extract part of a data type
Concatenation Adding and printing the characters of two strings.
Repetition multiple copies of the same string
in, not in
(membership
operator)
Using membership operators to check a particular
character is in string or not. Returns true if present.

• str='hello w'
• print(len(str))
• 7
• print(str[:])
• hello w
• print(str[::2])
• Hlow
• print(str[::-1])
• w olleh

Example
• Consider the string S=“Python Programming”
• Predict the output:
• s[-1]
• S[6:12]
• S[:4]
• S[:]
• S[5:5] , s[9:] ,s[0:5] , len(s)

in, not in (membership operator)

Lists
• List is an ordered sequence of items. Values in the list
are called elements / items.
• It can be written as a list of comma-separated items
(values) between square brackets[ ].
• Items in the lists can be of different data types.

Operations on lists
• Indexing
• Slicing
• Concatenation
• Repetitions
• Updation, Insertion, Deletion

Indexing Accessing the item in the particular position
Slicing Slice operator is used to extract part of a string, or some
part of a list Python
Concatenation Adding and printing the items of two lists.
Repetitions multiple copies of the same string
Updating the list Updating the list using index value
Inserting an element Inserting an element in 2nd position
Removing an element Removing an element by giving the element directly

Updating the list
Inserting an element
Removing an element
Note:
Update,Insert:Need
to give Position
Remove:give value
alone

Tuple
• A tuple is same as list, except that the set of elements is enclosed in
parentheses instead of square brackets.
• A tuple is an immutable list. i.e. once a tuple has been created, you can't
add elements to a tuple or remove elements from the tuple.
• Tuples are faster than lists

Basic Operations
• Indexing
• Slicing
• Concatenation
• Repetitions
Note:
concatenate
tuple (not "int")
to tuple

Dictionaries
• Lists are ordered sets of objects, whereas dictionaries are
unordered sets.
• Dictionary is created by using curly brackets. i,e. {}
• Dictionaries are accessed via keys and not via their
position.

Variables
• Rules:
• A variable allows us to store a value by assigning it to a name,
which can be used later.
• Named memory locations to store values.
• Programmers generally choose names for their variables that are
meaningful.
• It can be of any length. No space is allowed.
• We don't need to declare a variable before using it. In Python, we
simply assign a value to a variable and it will exist.

Assigning a single value to several variables simultaneously:
Assigning multiple values to multiple variables
a=b=c=10,20,"Ram"
print(c)
(10, 20, 'Ram')
print(a)
(10, 20, 'Ram')
a=b=c=100
print(a)
100
print(c)
100

Expressions and Statements
• Statements:
• Instructions that a Python interpreter can executes are called statements.
• A statement is a unit of code like creating a variable or displaying a value.
• Expressions:
• An expression is a combination of values, variables, and operators.
>>> n = 17
>>> print(n)
a=2
a+3+2
7
str=("Good"+"Morning")
print(str)
GoodMorning

Multiple assignments
• same value to multiple variables
• Assign multiple values to multiple variables
a=b=c=10
print(a)
10
print(b)
10
x, y, z = "Orange", "Banana", "Cherry"
print(x)
Orange

Comments
• Comments are the kind of statements that are written in the
program for program understanding purpose.
• In Python, we use the hash (#) symbol to start writing a comment.
• Python Interpreter ignores comment.
• If we have comments that extend multiple lines, one way of doing it
is to use hash (#) in the beginning of each line.
# This is comment line
print(“I love my country”)
percentage = (minute *
100) / 60 # calculating
percentage of an hour
#This is
#another example
#of comment statement

OPERATORS
• Operators are the constructs which can manipulate the value of operands.
• Consider the expression 4 + 5 = 9.
• Here, 4 and 5 are called operands and + is called operator

Types of Operators
• Arithmetic Operators
• Comparison (Relational) Operators
• Assignment Operators
• Logical Operators
• Bitwise Operators
• Membership Operators
• Identity Operators

Arithmetic operators
• They are used to perform mathematical operations like addition,
subtraction, multiplication etc

Operator Description
+ Addition Adds values on either side of the operator
- Subtraction Subtracts right hand operand from left hand operand.
* Multiplication Multiplies values on either side of the operator
/ Division Divides left hand operand by right hand operand
% Modulus Divides left hand operand by right hand operand and
returns remainder
** Exponent Performs exponential (power) calculation on operators
// Floor Division - The division of operands where the result is
the quotient in which the digits after the decimal point are
removed

Comparison (Relational) Operators
• Comparison operators are used to compare values.
• It either returns True or False according to the condition. Assume, a=10 and b=5
==,<
>
<=
>=
!=

Assignment Operators
• Assignment operators are used in Python to
assign values to variables.

Operator Description Example
= Assigns values from right side operands to
left side operand
c = a + b assigns value of a
+ b into c
+= Add
AND
It adds right operand to the left operand
and assign the result to left operand
c += a
is equivalent to c = c + a
-= Subtract
AND
It subtracts right operand from the left
operand and assign the result to left
operand
c -= a
is equivalent to c = c - a
*= Multiply
AND
It multiplies right operand with the left
operand and assign the result to left
operand
c *= a
is equivalent to c = c * a
**=
Exponent
AND
Performs exponential (power) calculation
on operators and assign value to the left
operand
c **= a
is equivalent to c = c ** a
//= Floor
Division
It performs floor division on operators and
assign value to the left operand
c //= a is equivalent to c = c
// a

Logical Operators
• Logical operators are the and, or, not operators
And True if both the operands are True
Or True if either of the operands is true
not True if operands is false

Bitwise Operators
• A bitwise operation operates on one or more bit patterns
at the level of individual bits
• Let x = 10 (0000 1010 in binary) and
y = 4 (0000 0100 in binary)

x = 10 (0000 1010 in binary) and
y = 4 (0000 0100 in binary)
& Bitwise AND X&Y= (0000 0000)
| Bitwise OR X|y= (0000 1110)
~ Bitwise Not -x=(1111 0101)
^ Bitwise XOR x ^ y =(1111 0001)
>> Bitwise right shift X >>2=(0000 0010)
<< Bitwise left shift X <<2=(0010 1000)

Membership Operators
• Evaluates to find a value or a variable is in the specified sequence
of string, list, tuple, dictionary or not.
• Let, x=[5,3,6,4,1]. To check particular item in list or not, in and not in
operators are used.

Identity Operators
• They are used to check if two values (or variables) are
located on the same part of the memory.
• If the two values are identical: True

Precedence of operators
• When an expression contains more than one operator, the order of
evaluation depends on the order of operations.
• PEMDAS (Parentheses, Exponentiation, Multiplication, Division, Addition,
Subtraction)

Input function
• Input is data entered by user (end user) in the program.
• input () function
x=input("enter the name:")
enter the name:hhh
y=int(input("enter the number"))
enter the number 3

Output function
• Output can be displayed to the user using Print statement
print (expression/constant/variable)
print("Hello")
Hello
print(2+4)
6
print(6)
6

Type Casting(Type Conversion)
• Is the process of converting the value of one data type to another
Python Implicit Type Conversion
Python Explicit Type Conversion

Implicit Type Conversion
• In this, method, Python converts the data type into
another data type automatically. Users don’t have to
involve in this process.
a=10
b=12.0
c=a+b
print(c)
22.0

Explicit Type Conversion
• This involves converting a data type explicitly using predefined
functions like int(), float(), str(), etc., where the programmer
specifically directs the type of conversion required.
a=10
print(type(a))
<class 'int'>
print(float(a))
10.0
b=12.24
print(type(b))
<class 'float'>
print(int(b))
12
c=15.78
print(int(c))
15

• Convert string to int: (Value Error)
• Converting string to int datatype in Python with int() function. If the given
string is not number, then it will throw an error.
a="Hema"
print(int(a))
Traceback (most recent call last):
File "<pyshell#16>", line 1, in <module>
print(int(a))
ValueError: invalid literal for int() with base
10: 'Hema'
a="5"
print(int(a))
5

Formatting numbers and strings
price = 49
txt ="The price is {price} dollars"
print(txt)
Output:
The price is {price} dollars
price = 49
txt =f"The price is {price} dollars"
print(txt)
Output:
The price is 49 dollars

• Celsius to Fahrenheit:
F = [(C*9/5) +32]
• convert kilometers to miles
Miles=0.62*km

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