Python Basics: Strings, Comments, Variables

Introduction to Computers and Programming

• CSBP119: Algorithms & Problem Solving at CIT, UAEU is the context
• Discusses introduction, hardware, software, data storage, program execution, and Python usage

Introduction

• Computers are programmable and can perform tasks as directed by programs
• A program is a set of instructions for a computer to perform a task
• Software is commonly used to refer to programs
• A programmer designs, creates, and tests computer programs and is also known as a software developer

Hardware and Software

• Hardware comprises the physical devices of a computer
• A computer is a system of interconnected components

Typical major components of Hardware

• Central Processing Unit (CPU)
• Main memory
• Secondary storage devices
• Input and output devices

The CPU

• Central Processing Unit (CPU) runs programs and is the most important component
• Without the CPU, software cannot run
• Microprocessors are CPUs on small chips

Main Memory

• Main memory stores programs during execution and the data they use
• Also known as Random Access Memory (RAM)
• The CPU can quickly access data stored in RAM
• RAM is volatile memory for temporary storage while the program is running
• RAM contents are erased when the computer is turned off

Secondary Storage Devices

• Secondary storage holds data for extended periods
• Programs are usually stored in secondary storage and loaded into main memory when needed

Types of secondary memory

• Disk drives magnetically encode data on spinning circular disks
• Solid State Drives (SSDs) stores data in solid-state memory, is faster than disk drives, and has no moving parts
• Flash memory is portable with no physical disk
• Optical devices encode data optically

Input Devices

• Input is data collected by the computer from people and other devices
• Input devices collect data
• Keyboards, mice, touchscreens, scanners, and cameras are examples

Output Devices

• Output is data produced by the computer for users and other devices
• Output can be text, images, audio, or bit streams
• Output devices format and present the output
• Video displays and printers are examples

Software

• Software controls all computer operations
• General categories of software are application and system software
• Application software makes computers useful for everyday tasks
• Word processing, email, games, and web browsers are examples

How Computers Store Data

• All computer data is stored as sequences of 0s and 1s
• A byte is enough memory to store a letter or small number
• A byte is divided into eight bits
• A bit is an electrical component holding positive or negative charge, like an on/off switch
• The on/off pattern of bits in a byte represents the data stored

Storing Numbers

• A bit has two values: 0 and 1
• Computers use the binary numbering system
• A digit's position j has the value 2^(j-1)
• A binary number's value sums the position values of the 1s
• Byte size limits are 0 and 255
• 0 means all bits are off and 255 means all bits are on
• Multiple bytes are used to store larger numbers

Storing Characters

• Data stored in a computer must be stored as a binary number
• Characters are converted to numeric code, which is stored in memory
• ASCII is the most important coding scheme
• ASCII is limited to 128 characters
• Unicode is becoming a coding scheme standard
• Unicode is compatible with ASCII
• Unicode can represent characters for other languages

How a Program Works

• CPUs are designed to perform simple operations on data like reading, adding, subtracting, multiplying, and dividing numbers
• CPUs understand instructions written in machine language included in their instruction set
• Each CPU brand has its instruction set
• The CPU must perform many operations to carry out meaningful calculations

How a Program Works (cont'd.)

• Programs must be copied from secondary memory to RAM each time the CPU executes it
• The CPU executes programs in a cycle
• The steps include fetch, decode, and execute
• Fetch involves reading the next instruction from memory into CPU
• Decode means the CPU decodes the fetched instruction to determine operation
• Execute is performing the operation

From Machine Language to Assembly Language

• It is impractical for people to write in machine language
• Assembly language uses short words (mnemonics) for instructions, instead of binary numbers, making it easier for programmers
• Assemblers translate assembly language into machine language for execution by CPU

High-Level Languages

• Low-level language is close to machine language
• Assembly language is an example
• High-level languages allow simple creation of powerful and complex programs
• No need to know CPU specifics or write many instructions
• More intuitive to understand

Key Words, Operators, and Syntax: an Overview

• Key words are predefined words for writing programs in high-level language and each has a specific meaning
• Operators perform operations on data such as arithmetic
• Syntax is the set of rules for writing programs
• A statement is an individual instruction in a high-level language

Compilers and Interpreters

• Programs in high-level languages must be translated into machine language to be executed
• A compiler translates high-level language programs into separate machine language programs
• The Machine language programs an be executed at any time

Compilers and Interpreters (cont'd.)

• An interpreter translates and executes instructions in a high-level language program
• The Python language is interpreted
• The interpreter interprets one instruction at a time
• There is no separate machine language program
• Source code is statements written by a programmer
• A syntax error prevents code from being translated

Using Python

• Python must be installed and configured before use
• Included is the Python interpreter
• The Python interpreter can be used in two modes
• Interactive, to enter statements
• Script, to save statements in a Python Script

Interactive Mode

• A prompt indicates the interpreter is ready
• The prompt reappears after statement is executed
• Error messages are displayed after incorrectly typed statements
• Interactive mode is a good way to learn Python

Writing Python Programs and Running Them in Script Mode

• Statements entered in interactive mode are not saved as programs
• To use a program, it must use script mode
• First, save Python statements in a file
• The filename should have a ".py" extension
• Run the file, or script, by typing “python filename” at the operating system command line

Summary

• Main hardware components of the computer, and types of software
• How data is stored in a computer
• Basic CPU operations and machine language
• Fetch-decode-execute cycle
• Complex languages and their translation to machine code
• Python installation and Python interpreter modes

Input, Processing, & Output

• Designing a Program
• Input, Processing, and Output
• Displaying Output with the “print” Function
• Comments
• Variables
• Reading Input from the Keyboard
• Performing Calculations
• More About Data Output
• Named Constants
• Introduction to Turtle Graphics

Designing a Program

• Programs must be designed before written
• Program development cycle includes steps such as design, code writing, error correction, testing, and correcting logic errors
• Determine steps to perform a task then break it down into a series of steps
• An algorithm lists logical steps to be order taken

Pseudocode

• Pseudocode is fake code and an informal language without syntax rules
• It is not meant to be compiled or executed, but is used to create a model program
• There is no need to worry about syntax errors which allows one to focus on the design
• Pseudocode can be translated into actual code in any programming language
• The general order is input, processing and then output

Example Algorithm in Pseudocode

• Input the number of hours worked
• Input the hourly pay rate
• Calculate gross pay as the number of hours worked times hourly pay rate
• Display the gross pay

Flowcharts

• Flowcharts graphically depict steps in a program
• Ovals are terminal symbols
• Parallelograms are input and output symbols
• Rectangles are process symbols
• Symbols are connected by arrows that represent the flow

Input, Processing, and Output

• Computers typically perform a three-step process
• Receive input
• Perform some process on the input
• Produce output
• Input is any running program data
• Processing is what a program performs on input
• An example mathematical calculation
• Hours worked, hourly pay rate are both examples of input
• Multiply hours worked by hourly pay rate is processing
• Gross pay is the output

Functions

• A function is a section of prewritten code performing an operation
• An argument provides data to a function
• program operates on the order they appear
• The operate from top to bottom

Example: Displaying Output with the print Function

• Syntax: print(’Hello World’)
• The print function displays output to the screen
• “Hello World” is the argument which is the screen output

Strings and String Literals

• A string is a sequence of characters, being zero or more, used as data
• A string is a type of data
• A string literal is a string appearing in actual code

Rules for String Literals

• Must be enclosed in single (') or double (") quote marks
  • Example: 'Hello World', "Hello world"
• String literals can be enclosed in triple quotes (""" or ''')
• Example: print("""I can display 'single' and "double" quotes here""")
• Enclosed strings can contain both single and double quotes and can have multiple lines

Examples

• print ('Hello World')
• print ("I can display single 'quotes' here!")
• print ('I can display double "quotes" here')
• print ("""I can display 'single' and "double" quotes here""")

Output:

• Hello World
• I can display single 'quotes' here!
• I can display double "quotes" here
• I can display 'single' and "double" quotes here

Comments

• Comments are explanatory notes within the program that are ignored by the interpreter
• Start with "#" character

End Line Comments

• Display at the end of the line of code
• Example: print ('Hello World') #diaplay statement

Variables

• A variable stores a value in computer memory
• Variables are used to access and manipulate stored memory data
• Variables reference the value they represent
• An assignment statement creates a variable and makes it reference data

Using Assignment Statements

• The general format is variable = expression
  • Example: age = 29
• Assignment operators feature the "=" sign

Program with Variables

• #this program creates two variables
• width = 10
• length = 5
• print('width') #displays the string width
• print(width) #displays the variable width

Program Output

- width
- 10
- 5

Variables (cont'd.)

• Using assignment statements the receiving variables must be on the left
• Variables can be passed as an argument to a function
• Variable names must not be in quotation marks

Variable Naming Rules

1. Variable names cannot be a Python key word
2. Variable names cannot contain spaces
3. First character must be a letter or underscore
4. After the first character can use letters, digits, or underscores
5. Variable names are case sensitive
6. It should reflect its use

Displaying Multiple Items with the Print Function

• Python can display multiple items
• Items are separated by comas
• The program displays in order
• Items are automatically separated by a space
• Use "end=" to change a printed string termination
• Use "sep=" to change separator between printed string

Example

width" = 10
length =5
print ( 'the width is’, 'width’ )
print("The length is ', length)

Output:
The with is 10
The length is 5

Variable Reassignment

Variables can change values while program is running

-garbage collection removes unused values

• Variables can refer to item in type and the type can be reassigned

Numeric Data Types, Literals, and the str Data Type

• Data types categorize values in memory
• Ints store integer and floats store string
• Numeric literal are num values with in a program
• No decimal points are integers but other wise can store float
• Operations depending on the datat type

Numerical Data Types

- Value =2.6 print int (Value)

OUPUT: 2

Reading Input from the Keyboard

• Most programs utilize user input that is read from the built in keyboard
• Returns data only as a string
• Variable= Input prompt example
• Does not already displays space after prompt
• Variable is an output while prompt is the user interaction

Example

"print('Hello', name) #then displays a greeting #first displays the prompt and store the input in name name=input("what is your name? ") #then display a greeting print('Hi', name)"

OUTPUT: what is your name? Holly Holly is hi

Reading Numbers with the input Function

• The Input function returns always a string
• Built in functions are able to convert between datatypes
  • Example in < (items) converts time to int
  • Float function (items) converts item to float
• Nested functions calls have general for mat function one(funcionTwo (arguments.
  • Types conversion only works if the item is a valid number value

Performing Calculations

• math expression performals some calculations by providing a value by being
  • MATH tool
  • OPERANDS.
  • The results assign variables

The Math operators follow

(+)Addition (-)Subtraction (*)Multiplication (/)Division (**) = Raised

"Rate= (float (input ‘ is your hourly rate is’?)

rate= float (Input ‘what hourly rates?)"

Inter Vs Flat

• Inter division truncate = 5//2 #Integer Point display number

Result

Point=6/8=Float point

More example Values for display math operators

1. (+) (5+2) *4=26
2. (*) 10/(3-@) =/
3. (Float) =2
4. % remainder operators

Mixed-Type Expressions and Data Type Conversion

• Int and floa are an impory type
• A number is a temporatry can convert to the floating point
• A type conversion can store from a plot but may cases a traction

Examples

MixedType Examples

“ value=0.9 point

“print (int Value ()

1. Multiline contamination charectors

Result Val 1* (4+ val 4 *. Val

Turtle Graphic

Python graphic model displays code with a smaller cursor displays the tools

""import turtle Turtle forward (50) Turtle pensue (5) """

###Summary

• Designing programs and cycles
• Displaying multiple items with print functions-
• Using comments, variables, and name
• Perform math calculation
• Turtles graphics system

Booleans Eprression

Bool expressions use the following values

• Relationals

• equals -==Equals two the value

The Statement

" - Is the statement if condition

• Block 1 is the other statement. Bool expression "
• if score >= 90 # score is a b
• print #score equal print to a

Relational Operators

A relation operation relation weather expression is bwetwwn to values

Comparing Stings

• if name 1 name 2 print
• • Copyright c pearson value

logcial operation

“Bool operators and, O R connect Bool varible

1 If scarry and “

Optional Slides

“turtles graphics is system by adding small cursives You ca use that Turtle turtle #Import model Turtle for word (344) Turtle side true (3 points)

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