UNIT-1 : 20ACS04 – PROBLEM SOLVING AND PROGRAMMING USING PYTHON

20ACS04 –
PROBLEM SOLVING AND
PROGRAMMING USING
PYTHON
PREPARED BY
Mr. P. NANDAKUMAR
ASSISTANT PROFESSOR,
DEPARTMENT OF INFORMATION TECHNOLOGY,
SVCET.

COURSE CONTENT
UNIT-I
INTRODUCTION TO PROBLEM SOLVING, EXPRESSION AND DATA
TYPES
Fundamentals: what is computer science - Computer Algorithms - Computer
Hardware - Computer software - Computational problem solving using the Python
programming language - Overview of Python, Environmental Setup, First program
in Python, Python I/O Statement. Expressions and Data Types: Literals, Identifiers
and Variables, Operators, Expressions. Data types, Numbers, Type Conversion,
Random Number.
Problem solving: Restaurant Tab calculation and Age in seconds.

FUNDAMENTALS OF COMPUTERSCIENCE
 Computer Science is the study of computers and computational
systems.
 Unlike electrical and computer engineers, computer scientists deal
mostly with software and software systems; this includes their
theory, design, development, and application.
 Computer algorithms
 Computer hardware
 Computer software

COMPUTER ALGORITHMS
 An algorithm is a procedure used for solving a problem or
performing a computation.
 Algorithms act as an exact list of instructions that conduct specified
actions step by step in either hardware- or software-based routines.
 Algorithms are widely used throughout all areas of IT.

COMPUTER HARDWARE
 Computer hardware is the physical components that a computer
system requires to function.
 It encompasses everything with a circuit board that operates within a
PC or laptop; including the motherboard, graphics card, CPU
(Central Processing Unit), ventilation fans, webcam, power supply,
and so on.

FUNDAMENTAL HARDWARE COMPONENTS

COMPUTER SOFTWARE
 Software is a set of instructions, data or programs used to operate
computers and execute specific tasks.
 It is the opposite of hardware, which describes the physical aspects
of a computer.
 Computer software examples include operating systems, which
allow for easy use of a computer's processing power, as well as
applications like Notepad and Firefox.
 Software is a generic term used to refer to applications, scripts and
programs that run on a device.

Ada Lovelace “The First Computer
Programmer”

COMPUTATIONAL PROBLEM SOLVING USING THE PYTHON PROGRAMMING LANGUAGE
 Problem Solving with Python is a module where students learn
Computational Thinking strategies, problem solving techniques, and
fundamental coding concepts using the Python programming
language.
 Computational problem solving is the iterative process of
developing computational solutions to problems.
 These solutions are expressed as a logical sequence of steps (i.e.
programs) for others to understand and for computers to execute.

PROCESS OF COMPUTATIONAL PROBLEM SOLVING

INTRODUCTIONTO PYTHON
 Python is a
 cross-platform programming language
 free and open source
 general-purpose interpreted, interactive, object-oriented, and
high-level programming language
 Python was created by “Guido Van Rossum” in the year 1991
(late 1980’s)
 Designed to be easy as well as fun, the name "Python" is a nod to
the British comedy group Monty Python.

Python Environmental Setup
 Getting Python
 The most up-to-date and current source code, binaries, documentation,
news, etc., is available on the official website of Python
https://www.python.org/
 Windows Installation
 Here are the steps to install Python on Windows machine.
 Open a Web browser and go to https://www.python.org/downloads/.
 Run the downloaded file. This brings up the Python install wizard,
which is really easy to use. Just accept the default settings, wait until the
install is finished, and you are done.
https://www.tutorialspoint.com/python/python_environment.htm

 Python Features:
Easy-to-learn
Easy-to-read
Easy-to-maintain
A broad standard library
Interactive mode
Portable
Extendable
Databases
GUI Programming
Scalable

 Applications of Python:
Web Development
Game Development
Machine Learning and Artificial Intelligence
Data Science and Data Visualization
Desktop GUI
Web Scraping Applications
Business Applications
Audio and Video Applications
CAD Applications
Embedded Applications
Top Python Applications
(2023)

Starting the Python
 Two ways:
1. Immediate mode
Typing python code in the command line >>>
2. Script mode
 Typing python code in a file, such a file is called script.
 Save script as filename.py (ends with .py extension – denotes
python file)

The IDLE Python Development Environment
 IDLE is an integrated development environment ( IDE ).
 An IDE is a bundled set of software tools for program development.
 This typically includes an editor for creating and modifying
programs, a translator for executing programs, and a program
debugger.
 A debugger provides a means of taking control of the execution of a
program to aid in finding program errors.

The Python Standard Library
 The Python Standard Library is a collection of built-in modules ,
each providing specific functionality beyond what is included in the
“core” part of Python.
 In order to utilize the capabilities of a given module in a specific
program, an import statement is used in the below figure.

A Bit of Python
Variables
 A simple description of a variable is “a name that is assigned to a
value,” as shown below,
 n = 5, variable n is assigned the value 5
Some Basic Arithmetic Operators
 The common arithmetic operators in Python are + (addition), -
(subtraction), * (multiplication), / (division), and **
(exponentiation).
 10 + 20 25 - 15 20 / 10
 5 * 10 (5 times 10) 2 ** 4 (2 to the 4th power)
 10 * (20+1 5) CORRECT 10(20+1 5) INCORRECT

Basic Input and Output
 In Python, the input function is used for this purpose,
name = input('What is your name?: ')
 Characters within quotes are called strings. This particular use of a
string, for requesting input from the user, is called a prompt.
 The input function displays the string on the screen to prompt the user
for input,
What is your name?: Charles
The underline is used here to indicate the user’s input.
 The print function is used to display information on the screen in
Python. This may be used to display a message,
>>> print('Welcome to My First Program!’)
Welcome to My First Program!
In Python, input is used to request and get information from the
user, and print is used to display information on the screen.

Learning How to Use IDLE
 This program utilizes the following concepts:
 creating and executing Python programs
 input and print
 First, to create a Python program file, select New Window from the
File menu in the Python shell as shown in Figure.

 When finished, save the program file by selecting Save As under the
File menu, and save in the appropriate folder with the name
MyFirstProgram.py.

 To run the program, select Run Module from the Run menu (or simply
hit function key F5.
 If you have entered the program code correctly, the program should
execute as shown in below Figure.

 If, however, you have mistyped part of the program resulting in a
syntax error (such as mistyping print), you will get an error message
similar to that in the following Figure.

FIRST PYTHON PROGRAM
Let us execute a Python "Hello, World!" Programs in different modes of
programming.
 Python - Interactive Mode Programming
 We can invoke a Python interpreter from command line by typing
python at the command prompt as following −
 $ python
Python 3.6.8 (default, Mar 31 2023, 09:13:53)
Type "help", "copyright", "credits" or "license" for more information.
>>>

 Here >>> denotes a Python Command Prompt where you can
type your commands. Let's type the following text at the Python
prompt and press the Enter −
 >>> print ("Hello, World!")
Hello, World!

 Python - Script Mode Programming
 We can invoke the Python interpreter with a script parameter which
begins the execution of the script and continues until the script is
finished. When the script is finished, the interpreter is no longer
active.
 Let us write a simple Python program in a script which is simple text
file. Python files have extension .py. Type the following source code
in a sample.py file −
 print ("Hello, World!")

 We assume that you have Python interpreter path set in PATH
variable. Now, let's try to run this program as follows −
 $ python sample.py
 This produces the following result −
Hello, World!

INPUT AND OUTPUT STATEMENTS IN PYTHON
The input() function helps to enter data at run time by the user
and the output function print() is used to display the result of the
program on the screen after execution.
Syntax:
 input('prompt’)
 where prompt is an optional string that is displayed on the
string at the time of taking input.

INPUT AND OUTPUT IN PYTHON
Example 1: Python get user input with a message
# Taking input from the user
name = input("Enter your name: ")
# Output
print("Hello, " + name)
print(type(name))

INPUT AND OUTPUT IN PYTHON
Example 2: Integer input in Python
# Taking input from the user as integer
num = int(input("Enter a number: "))
add = num + 1
# Output
print(add)

Data and Expressions
FUNDAMENTAL CONCEPTS
Literals
 A literal is a sequence of one of more characters that stands for itself,
such as the literal 12.
 A literal is a sequence of one or more characters that stands for
itself.
Numeric Literals
 A numeric literal is a literal containing only the digits 0–9, an optional
sign character ( 1 or 2 ), and a possible decimal point.

Built-in format Function
 The built-in format function can be used to produce a numeric string
version of the value containing a specific number of decimal places.
>>>12/5 >>>5/7
2.4 0.7142857142857143
>>> format(12/5, '.2f’) >>>format(5/7, '.2f’)
'2.40’ '0.71'
 The built-in format function can be used to produce a numeric
string of a given floating-point value rounded to a specific number
of decimal places.

String Literals
 Numerical values are not the only literal values in programming. String
literals , or “ strings ,” represent a sequence of characters,
'Hello’ 'Smith, John’ "Baltimore, Maryland 21210“
 A string literal, or string, is a sequence of characters denoted by a
pair of matching single or double (and sometimes triple) quotes in
Python.
String Literal Values

Definitions
 Unicode is capable of representing over 4 billion different characters,
enough to represent the characters of all languages, past and present.
Python’s (default) character encoding uses UTF-8, an eight-bit
encoding that is part of the Unicode standard.
 Control characters are nonprinting characters used to control the
display of output (among other things).
 An escape sequence is a string of one or more characters used to
denote control characters.

Control Characters
 Control characters are special characters that are not displayed on the
screen.
 An escape sequence begins with an escape character that causes the
sequence of characters following it to “escape” their normal meaning.
 The backslash () serves as the escape character in Python.
 For example, the escape sequence 'n', represents the newline control
character , used to begin a new screen line. An example of its use is
given below,
print('HellonJennifer Smith’)
which is displayed as follows, Hello
Jennifer Smith

String Formatting
 The format function can be used to control how strings are displayed.
 the format function has the form,
format(value, format_specifier)
Example:
Left Justified: format('Hello', ' < 20') ➝ 'Hello
Right Justified: format('Hello', ' > 20') ➝ ' Hello'
 Built-in function format can be used to control how strings are
displayed.

Implicit Line Joining
 Matching parentheses, square brackets, and curly braces can be used to
span a logical program line on more than one physical line.
 For example, the following two program lines are treated as one
logical line,
print('Name:', student_name, 'Address:', student_address,
'Number of Credits:', total_credits, 'GPA:', current_gpa)
 Matching quotes (except for triple quotes, covered later) must be on
the same physical line. For example, the following will generate an
error,
print('This program will calculate a restaurant tab for a couple
with a gift certificate, and a restaurant tax of 3%')

Explicit Line Joining
 Program lines may be explicitly joined by use of the backslash ().
 In addition to implicit line joining, program lines may be explicitly joined
by use of the backslash () character.
 Program lines that end with a backslash that are not part of a literal string
(that is, within quotes) continue on the following line,
numsecs_1900_dob = ((year_birth - 1900) * avg_numsecs_year) +
((month_birth - 1) * avg_numsecs_month) +
(day_birth * numsecs_day)

VARIABLES
What Is a Variable?
 A variable is a name (identifier) that is associated with a value, as for
variable num depicted in the following.
 A variable can be assigned different values during a program’s
execution—hence, the name “variable”.
 Variables are assigned values by use of the assignment operator , =.
Variable Update

VARIABLES
 Variables must be declared before they are used in program.
 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.
 Example:
counter = 100 # An integer assignment
miles = 1000.0 # A floating point
name = "John" # A string
print (counter)
print (miles)
print (name)

VARIABLES
Variable Assignment (to another variable)
 A variable is a name that is associated with a value.
 The assignment operator, =, is used to assign values to variables.
 An immutable value is a value that cannot be changed.
 All input is returned by the input function as a string type. Built-in
functions int() and float() can be used to convert a string to a
numeric type.

IDENTIFIERS
What Is an Identifier?
 An identifier is a sequence of one or more characters used to provide a
name for a given program element.
 Variable names line, num_credits, and gpa are each identifiers.
 The underscore character, _, is also allowed to aid in the readability of
long identifier names. It should not be used as the first character
 Spaces are not allowed as part of an identifier.
Identifier Naming

Identifiers and Keywords in Python
Identifiers: Set of valid strings
Rules for identifiers in python
 Identifiers can be combination of uppercase and lowercase letters, digits or an
underscore(_). So myVariable, variable_1, variable_for_print all are valid python
identifiers.
 An Identifier can not start with digit. So while variable1 is valid, 1variable is not
valid.
 We can’t use special symbols like !,#,@,%,$ etc in our Identifier.
 Identifier can be of any length.
Keywords: Different version of python has different keywords
(Updated python 3 version has 33 keywords)
Some of them are: and elif for def from del
break print try return continue

Keywords and Other Predefined Identifiers in Python
 A keyword is an identifier that has predefined meaning in a
programming language and therefore cannot be used as a “regular”
identifier. Doing so will result in a syntax error.
>>> and = 10
SyntaxError: invalid syntax
 The keywords in Python are listed in the following Figure,

KEYWORDS AND OTHER PREDEFINED IDENTIFIERS IN
PYTHON
 There are other predefined identifiers that can be used as regular
identifiers, but should not be.
 This includes float, int, print, exit, and quit, for example.
 A simple way to check whether a given identifier is a keyword in Python
is given below,
>>> 'exit' in dir(__builtins__) >>> 'exit_program' in dir(__builtins__)
True False

OPERATORS
What Is an Operator?
 An operator is a symbol that represents an operation that may be
performed on one or more operands.
 For example, the + symbol represents the operation of addition.
 An operand is a value that a given operator is applied to, such as
operands 2 and 3 in the expression 2 + 3.
 A unary operator operates on only one operand, such as the negation
operator in -12.
 A binary operator operates on two operands, as with the addition
operator.

OPERATORS
Arithmetic Operators
 Python provides the arithmetic operators given in the following Figure.
 The + , - , * (multiplication) and / (division) arithmetic operators
perform the usual operations.
 Note that the - symbol is used both as a unary operator (for negation)
and a binary operator (for subtraction).

OPERATORS
Other Operators
 Python also includes an exponentiation (**) operator. Integer and
floating-point values can be used in both the base and the exponent.
2**4 ➝ 16
2.5 ** 4.5 ➝ 61.76323555016366
 Python provides two forms of division:
1. True division that is denoted by a single slash, /.
2. Truncating division is denoted by a double slash, //.
Division Operators in Python

OPERATORS
Other Operators
 Lastly, the modulus operator (%) gives the remainder of the division
of its operands, resulting in a cycle of values. This is shown in the
following Figure.
The Modulus Operator

OPERATORS
Summary
 The division operator, /, produces “true division” regardless of its
operand types.
 The truncating division operator, //, produces either an integer or
float truncated result based on the type of operands applied to.
 The modulus operator (%) gives the remainder of the division of its
operands.

EXPRESSIONS AND DATA TYPES
What Is an Expression?
 An expression is a combination of symbols that evaluates to a value.
 Expressions, most commonly, consist of a combination of operators and
operands,
4 + (3 * k)
 An expression can also consist of a single literal or variable.
 Expressions that evaluate to a numeric type are called arithmetic
expressions.
 A subexpression is any expression that is part of a larger expression.
 Subexpressions may be denoted by the use of parentheses ().

Operator Precedence
 The way we commonly represent expressions, in which operators appear
between their operands, is referred to as infix notation.
 For example, the expression 4 + 3 is in infix notation since the +
operator appears between its two operands, 4 and 3.
 There are other ways of representing expressions called prefix and
postfix notation, in which operators are placed before and after their
operands, respectively.
Operator Precedence of Arithmetic Operators in Python

Operator Associativity
 Operator associativity is the order that operators are applied when
having the same level of precedence, specific to each operator.
What Is a Data Type?
 A data type is a set of values, and a set of operators that may be
applied to those values.
 For example, the integer data type consists of the set of integers, and
operators for addition, subtraction, multiplication, and division, among
others.
 Integers, floats, and strings are part of a set of predefined data types
in Python called the built-in types .

There are two approaches to data typing in programming languages.
 In static typing, a variable is declared as a certain type before it is used,
and can only be assigned values of that type.
 Python, however, uses dynamic typing.
 In dynamic typing, the data type of a variable depends only on the type
of value that the variable is currently holding.
 Thus, the same variable may be assigned values of different type during
the execution of a program.
Mixed-Type Expressions
 A mixed-type expression is an expression containing operands of
different type.

 Values can be converted in one of two ways—by implicit (automatic)
conversion, called coercion , or by explicit type conversion.
Coercion vs. Type Conversion
 Coercion is the implicit (automatic) conversion of operands to a
common type.
2 + 4.5 ➝ 2.0 + 4.5 ➝ 6.5 safe (automatic conversion of int to
float)
 Type conversion is the explicit conversion of operands to a specific
type.
float(2) + 4.5 ➝ 2.0 + 4.5 ➝ 6.5
2 + int(4.5) ➝ 2 + 4 ➝ 6

Conversion Functions int() and float() in Python

“RESTAURANT TAB CALCULATION”
This program utilizes the following programming features:
 variables
 keyboard input
 built-in format function
 type conversion functions
The program in next page calculates a restaurant tab for a couple
based on the use of a gift certificate and the items ordered.

RESTAURANT TAB CALCULATION PROGRAM

UNIT-1 : 20ACS04 – PROBLEM SOLVING AND PROGRAMMING USING PYTHON

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