Python Programming

PYTHON PROGRAMMING
Python Basics
Dr.T.M.SARAVANAN
Associate Professor,
Department of Computer Applications,
Kongu Engineering College,
Perundurai – 638 060.

Introduction to pythonprogramming
• High level, interpreted language
• Object-oriented
• General purpose
• Web development (like: Django, and
Bottle),
• Scientific and Mathematical Computing
(Orange, SciPy, NumPy)
• Desktop graphical user Interfaces
(Pygame, Panda3D).

Other features of python includes the following:
• Simple language which is easier to learn
• Free and open source
• Portability
• Extensible and embeddable
• Standard large library

• Created by Guido van Rossum in 1991
• Why the name Python?
• Not after a dangerous snake.
• Rossum was fan of a famous TV Show comedy
series from late Eighties.
• The name "Python" was adopted from the same
series "Monty Python's Flying Circus".

Python’s Benevolent Dictator For Life
“Python is an experiment in how
much freedom programmers
need. Too much freedom and
nobody can read another's code;
too little and expressiveness is
endangered.”
- Guido van Rossum

Reasons toChoose Python asFirstLanguage
• Simple Elegant Syntax
• Not overly strict
• Expressiveness of the language
• Great Community and Support

Installation of Python inWindows
• Go to Download Python page on the official
site (python.org/downloads/) and click
Download Python 3.9.4.
• When the download is completed, double-click
the file and follow the instructions to install it.
• When Python is installed, a program called
IDLE is also installed along with it. It provides
graphical user interface to work with Python.

• Open IDLE, Write the following code below
and press enter.
print("Hello,W
orld!")
• To create a file in IDLE, go to File > New
Window (Shortcut: Ctrl+N).
• Write Python code and save (Shortcut: Ctrl+S)
with .py file extension like: hello.py or your-
first-program.py
print("Hello,World!")
• Go to Run > Run module (Shortcut: F5) and
you can see the output.

Python Code Execution
Python’s traditional runtime execution model: source code you
type is translated to byte code, which is then run by the Python
Virtual Machine. Your code is automatically compiled, but then
it is interpreted.
Source code extension is .py
Byte code extension is .pyc (compiled python code)

Difference Between Python 2.x & 3.x

Few Important Things toRemember
• To represent a statement in Python, newline
(enter) is used.
• Use of semicolon at the end of the
statement is optional (unlike languages
like C/C++)
• In fact, it's recommended to omit
semicolon at the end of the statement
in Python
• Instead of curly braces { }, indentations are
used to represent a block

PythonKeywords
• Keywords are the reserved words(can not be
used as a identifier) in Python
• Are case sensitive

PythonIdentifiers
• Name given to entities like class, functions,
variables etc. in Python
• Rules for writing identifiers
• Can be a combination of letters in lowercase (a to
z) or uppercase (A to Z) or digits (0 to 9) or an
underscore (_)
• myClass, var_1 and print_this_to_screen, all are
valid examples
• Cannot start with a digit
• 1variable is invalid, but variable1 is perfectly fine
• Keywords cannot be used as identifiers
• Cannot use special symbols like !, @, #, $, % etc.
in our identifier
• Can be of any length.

Things to careabout
• Python is a case-sensitive language.
• Variable and variable are not the same.
• Multiple words can be separated
using an underscore,
this_is_a_long_variable

PythonStatement
• Instructions that a Python interpreter can
execute are called statements.
• Two types
• Single line statement:
• For example, a = 1 is an assignment statement
• Multiline statement:
• In Python, end of a statement is marked by a
newline character.
• So, how to make multiline statement?

• Technique1:
• make a statement extend over multiple lines
with the line continuation character ().
• For example:
a
=
1+
2+
3+

4+
5+
6+

7+8+9

• Technique2:
• make a statement extend over multiple lines
with the parentheses ( )
• For example:
a=(1+2+3+
4+5+6+
7+8+9)

• Technique3:
• make a statement extend over multiple lines with
the brackets [ ] and braces {
}.
• For example:
colors=['red',
'blue',
'green']

• We could also put multiple statements in a single
line using semicolons, as follows
a=1;b=2;c=3

PythonIndentation
• Most of the programming languages like C,
C++, Java use braces { } to define a block of
code
• Python uses indentation
• A code block (body of a function, loop etc.)
starts with indentation and ends with the
first un-indented line

Error due to incorrectindentation

PythonComments
• To make the code much more readable.
• Python Interpreter ignores comment.
• Two types of comment is possible in python:
• Single line comment and
• Multi-line comment

Single linecomment
• In Python, we use the hash (#) symbol to start
writing a comment.
• It extends up to the newline character

Multi-line comments
• Two way:
• By using # sign at the beginning of each line
• By using either ‘ ‘ ‘ or “ “ “ (most common)

PythonVariable
• a variable is a named location used to store data
in the memory.
• Alternatively, variables are container that hold
data which can be changed later throughout
programming

Declaring Variables
• In Python, variables do not need declaration to
reserve memory space.
• The "variable declaration" or "variable
initialization" happens automatically when
we assign a value to a variable.
• We use the assignment operator = to assign the
value to a variable.

Assigning same value to the multiplevariable

Assigning multiplevalues to multiplevariables

Constants
• Value that cannot be altered by the
program during normal execution.
• In Python, constants are usually declared and
assigned on a module
• And then imported to the file

Rules and Naming convention for
variables and constants
• Create a name that makes sense. Suppose,
vowel makes more sense than v.
• Use camelCase notation to declare a variable
• For example: myName, myAge, myAddress
• Use capital letters where possible to declare a
constant
• For example: PI,G,MASS etc.

• Never use special symbols like !, @, #, $, %,
etc.
• Don't start name with a digit.
• Constants are put into Python modules
• Constant and variable names should have
combination of letters in lowercase (a to z) or
uppercase (A to Z) or digits (0 to 9) or an
underscore (_).
• For example: snake_case, MACRO_CASE,
camelCase, CapWords

Literals
Literal is a raw data given in a variable or constant.
In Python, there are various types of literals they
are as follows:
1. Numeric literals – Interger, Float, Complex
2. String literals – String, Character
3. Boolean literals – True or False
4. Special literals – None(Null Value)
5. Literal collections – List, Tuple, Dictionary and Set

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Text Type: str
Numeric Types: int, float, complex
Sequence Types: list, tuple, range
Mapping Type: dict
Set Types: set, frozenset
Boolean Type: bool
Binary Types: bytes, bytearray, memoryview
Built-in Data Types
In programming, data type is an important concept.
Variables can store data of different types, and different types can do different things.
Python has the following data types built-in by default, in these categories:

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Example Data Type
x = "Hello World" str
x = 20 int
x = 20.5 float
x = 1j complex
x = ["apple", "banana", "cherry"] list
x = ("apple", "banana", "cherry") tuple
x = range(6) range
x = {"name" : "John", "age" : 36} dict
x = {"apple", "banana", "cherry"} set
x = frozenset({"apple", "banana", "cherry"}) frozenset
x = True bool
x = b"Hello" bytes
x = bytearray(5) bytearray
x = memoryview(bytes(5)) memoryview
Setting the Data Type
In Python, the data type is set when you assign a value to a
variable:

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Setting the Specific Data Type
If you want to specify the data type, you can use the following
constructor functions:
Example Data Type
x = str("Hello World") str
x = int(20) int
x = float(20.5) float
x = complex(1j) complex
x = list(("apple", "banana", "cherry")) list
x = tuple(("apple", "banana", "cherry")) tuple
x = range(6) range
x = dict(name="John", age=36) dict
x = set(("apple", "banana", "cherry")) set
x = frozenset(("apple", "banana", "cherry")) frozenset
x = bool(5) bool
x = bytes(5) bytes
x = bytearray(5) bytearray
x = memoryview(bytes(5)) memoryview

DataTypes
• In python data types are classes and variables
are instance (object) of these classes
• Different types of data types in python are:
• Python numbers
• Python lists
• Python tuples
• Python strings
• Python sets
• Python dictionary

PythonList
• Ordered sequence of items
• Can contain heterogeneous data
• Syntax:
• Items separated by commas are
enclosed within brackets [ ]
• Example: a= [1,2.2,'python']

Extracting elements from thelist

• Note: Lists are mutable, meaning, value of
elements of a list can be altered.

PythonTuple
• Same as list but immutable.
• Used to write-protect the data
• Syntax:
• Items separated by commas are
enclosed within brackets ( )
• Example:
• t = (5,'program', 1+3j)

PythonStrings
• use single quotes or double quotes to represent strings.
• Multi-line strings can be denoted using triple quotes, ''' or """.
• Strings are also immutable.

PythonSet
• Unordered collection of unique items
• defined by values separated by comma inside
braces { }

• Set have unique values. They eliminate
duplicates.
• Example:

• Since, set are unordered collection, indexing has
no meaning.
• Hence the slicing operator [] does not work.
• Example:

PythonDictionary
• An unordered collection of key-value pairs.
• Must know the key to retrieve the value.
• Are defined within braces {} with each item
being a pair in the form key: value
• Key and value can be of any type

Conversion between datatypes
• Conversion can be done by using different
types of type conversion functions like:
• int(),
• float(),
• str() etc.

Convert one sequence toanother

• To convert to dictionary, each element must be a
pair:

Python TypeConversion and TypeCasting
• The process of converting the value of one data
type (integer, string, float, etc.) to another data
type is type conversion
• Python has two types of type conversion.
• Implicit Type Conversion
• Explicit Type Conversion

• Type Conversion is the conversion of object
from one data type to another data type
• Implicit Type Conversion is automatically
performed by the Python interpreter
• Python avoids the loss of data in Implicit Type
Conversion
• Explicit Type Conversion is also called Type
Casting, the data types of object are
converted using predefined function by user
• In Type Casting loss of data may occur as
we enforce the object to specific data type

Implicit TypeConversion
• Automatically converts one data type to another
data type
• Always converts smaller data type to larger data
type to avoid the loss of data

Problem in implicit typeconversion

ExplicitTypeConversion
• Users convert the data type of an object to
required data type.
• Predefined functions like int(), float(), str(), etc.
are to perform explicit type conversion
• Is also called typecasting because the user
casts (change) the data type of the objects.
• Syntax :
• (required_datatype)(expression)
• Int(b)

Python Input, Output andImport
• Widely used functions for standard input and
output operations are:
• print() and
• input()

Python Output Using print()function

Output formatting
• Can be done by using the str.format() method
• Is visible to any string object
• Here the curly braces {} are used as
placeholders. We can specify the order in which
it is printed by using numbers (tuple index).

• We can even use keyword arguments to format
the string

• We can even format strings like the old printf()
style used in C
• We use the % operator to accomplish this

Input()function
• input() function to take the input from
the user.
• The syntax for input() is :
• input([prompt])
• where prompt is the string we wish to
display on the screen.
• It is optional

• Entered value 10 is a string, not a number.
• To convert this into a number we can use
int() or float() functions
• This same operation can be performed using the
eval(). It can evaluate expressions, provided the
input is a string.

PythonImport
• When our program grows bigger, it is a good
idea to break it into different modules.
• A module is a file containing Python definitions
and statements.
• Python modules have a filename and end with
the extension .py
• Definitions inside a module can be imported to
another module or the interactive interpreter in
Python
• We use the import keyword to do this

• import some specific attributes and functions
only, using the from keyword.

PythonOperators
• Operators are special symbols in Python that
carry out arithmetic or logical computation.
• The value that the operator operates on is
called the operand.
• For example:
>>> 2+3
5
• Here, + is the operator that performs addition.
• 2 and 3 are the operands and 5 is the output
of the operation.

Bitwiseoperators
• Bitwise operators act on operands as if they
were string of binary digits. It operates bit by
bit, hence the name.
• For example, 2 is 10 in binary and 7 is 111.
• In the table below: Let x = 10 (0000 1010 in
binary) and y = 4 (0000 0100 in binary)

Assignmentoperators
• Assignment operators are used in
Python to assign values to variables.
• a = 5 is a simple assignment operator that
assigns the value 5 on the right to the
variable a on the left.
• There are various compound operators in
Python like a += 5 that adds to the variable
and later assigns the same.
• It is equivalent to a = a + 5.

Specialoperators
• identity
operator
• membership
operator

Identity operators
• is and is not are the identity operators in Python.
• They are used to check if two values (or variables)
are located on the same part of the memory.
• Two variables that are equal does not imply that
they are identical.

Membership operators
• in and not in are the membership operators in
Python
• They are used to test whether a value or
variable is found in a sequence (string, list,
tuple, set and dictionary).
• In a dictionary we can only test for presence of
key, not the value

Python Programming

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