PLD EXAM (copy)

The Origin of Python

• Question: Where does the name "Python" come from?

  • Answer: The name comes from Monty Python’s Flying Circus, a comedy series enjoyed by Guido van Rossum, Python's creator.

  • Python's design philosophy emphasizes code readability and simplicity, reflecting creativity akin to the show.

Basic Definitions and Terminology

• Commands: A complete set of commands in a program is referred to as a "command list."

• Statements and Boolean Operations:

  • Python includes logical operators: and, or, not.

  • Important truths:

    • True + 1 evaluates to 2.

    • True and False evaluates to False.

    • True or False evaluates to True.

• Python’s Creator:

  • Created by Guido van Rossum in the late 1980s; first released in 1991.

  • Designed for simplicity and readability, minimizing programming complexity.

Python as an Interpreted Language

• Execution: Python is an interpreted language, executing code line-by-line by an interpreter.

  • This characteristic aids in testing, debugging, and facilitates prototyping and iterative development.

Commenting in Python

• Single-Line Comments: Start with the # symbol; essential for code readability.

• Multi-Line Comments: Use triple quotes (''' ... ''') to denote multi-line comments as Python lacks traditional symbols.

Python's High-Level Nature

• High-Level Language: Abstractions simplify interaction with complex computer processes.

  • Contrasts with low-level languages that operate close to hardware, making Python more user-friendly.

Data Types and Conditional Checks

• Type Checking: Use built-in functions like isinstance() to verify variable types (e.g., int, str).

  • Example: Checking if x is an integer:

    x = 10
    if isinstance(x, int):
        print("Integer")
    else:
        print("Not Integer")

Printing and Formatting Outputs

• Separators in Print Statements: Use the sep parameter with print() to define separators:

  • Example: print("Python", "Programming", sep="-") results in "Python-Programming".

• End Parameter in Print: Change the ending character:

  • Example:

    print("Hello", end="@")
    print("World")

    Results in "Hello@World".

Understanding Syntax and Errors

• Types of Errors:

  • Syntax Errors: Identified during compilation (e.g., missing parentheses).

  • Runtime Errors: Identified during program execution.

  • Example of syntax error: print("Hello World!")) causes SyntaxError due to extra parenthesis.

Basic Input and Output

• Taking Input: Use the input() function to gather user input, which returns a string. Converting to other types is common.

  • Example:

    user_input = input("Enter a number: ")
    print ("You entered:", int(user_input))

Control Structures: Loops and Conditionals

• While Loops: Repeat code while a condition holds true:

  • Example:

    X = 10
    while X > 0:
        X -= 1
        print(X)

    • Counts down from 9 to 0.

• For Loops: Used with ranges:

  • Example:

    for number in range(1, 6):
        if number % 2 != 0:
            print(number)

    • Outputs odd numbers: 1, 3, 5.

Identifiers and Naming Rules

• Identifiers: Must start with a letter (A-Z or a-z) or underscore (_), followed by letters, numbers, or underscores.

  • Valid identifier example: mile.

  • Invalid identifier example: $343.

Operators and Precedence

• Order of Operations: PEMDAS

  1. Parentheses

  2. Exponents

  3. Multiplication/Division

  4. Addition/Subtraction

  • Example:

    result = 2 + 2 ** 3 / 2

    • Evaluates as 2 + (8 / 2) = 6.0.

Error Handling and Debugging

• Common Errors: Syntax errors (like SyntaxError for structural issues) and NameError when names are not found.

• Example of a syntax error:

  print("Hello World!"))

  • Extra parenthesis causes a SyntaxError.

Working with Strings and Numbers

• Concatenation: Adding strings using +, but need to convert numbers:

  • Example:

    print("The answer is " + str(42))

Flow Control with Pseudocode and Logic

• Writing Algorithms: Use pseudocode or flowcharts to outline program structure.

  • Flowcharts represent paths and loops visually.

Python’s Flexibility in Programming Paradigms

• Supports Multiple Paradigms: Python accommodates object-oriented, functional, and procedural programming.

• Exponentiation: Symbol for exponentiation in Python is **.

  • Example:

    2 ** 3  # Results in 8

  • Do not use ^, which is a bitwise XOR.

Loop Behavior in Flowcharts

• If X = 8, "Yoyo" might print 7 times if the loop reduces X by 1 each time it prints.

• If X = 0 after a loop, it could signal a condition to print "Bye."

• If X = 10 and each iteration reduces X by 2 while printing, "Yoyo" would print 5 times.

Syntax Errors in Python

• Identifying Errors: Example of a syntax error,

  • Problematic string: ‘3\’, which can lead to issues in interpretation due to incomplete backslashes.

Mixing Strings and Numbers

• Addition Challenge: Adding string and number like ('123' + 4) causes an error. Convert using str() to add.

  • Example:

    print("123" + str(4)) # Output: 1234

Introduction to Flowchart Concepts

• Flowcharts: A method to graphically represent the steps of a process. Useful for planning and understanding programming logic.

Flowchart Symbols

• Basic Symbols:

  • Oval (Start/End): Marks start and end points (labeled "Start" and "End").

  • Rectangle (Process): Represents actions (e.g., calculations).

  • Diamond (Decision): Decision-making points (Yes/No conditions).

  • Parallelogram (I/O): Input/output operations.

  • Arrows: Show the flow direction between steps.

Understanding Flowchart Logic

• Analyzing Flowcharts:

  • Start at "Start" symbol and follow arrows sequentially.

  • At Decision points, follow the path based on the condition (True/False or Yes/No).

  • Review process steps till reaching "End".

Types of Flowcharts in Programming

• Sequential Flowcharts: Steps occur with no branching (e.g., fixed messages).

• Decision Flowcharts: Handle branching conditions, if-else logic. (e.g., positive/negative number checks).

• Looping Flowcharts: Represent repetitive tasks, while-for loops. (e.g., countdowns).

Example Flowcharts**

• Flowchart for Calculating Sum:

  1. Start

  2. Input: Get two numbers (num1, num2).

  3. Process: Calculate sum = num1 + num2.

  4. Output: Display sum.

  5. End.

• Flowchart for Even or Odd Check:

  1. Start

  2. Input: Get a number.

  3. Decision: Check if num % 2 == 0:

     • Yes: Output "Even".

     • No: Output "Odd".

     Here’s a breakdown of how it works:

     1. Start: The process begins here.

     2. Input: The program asks the user to enter a number (let's call it num).

     3. Decision: The program checks if the number divided by 2 has a remainder of 0 (this is done using the modulus operator %). This means it checks if num % 2 == 0.

        • If Yes: If the condition is true (i.e., the number is even), the program will output "Even".

        • If No: If the condition is false (i.e., the number is odd), the program will output "Odd".

     4. End: The process concludes here.

Interpreting Flowcharts with Loops and Conditions

• Flowchart Example: Example of counting down from 1 to 5 using a decision structure.

  • Start

  • Initialize count = 1

• Decision: Is count <= 5?

  • Yes: Print count; increment count.

  • No: End

  Here’s a breakdown of the steps:

  1. Start: This is where the process begins.

  2. Initialize count: We start by setting the count variable to 1 (count = 1). This tells the program that our starting point is 1.

  3. Decision: We then ask the question: "Is count less than or equal to 5?"

     • If the answer is Yes: We print the current value of count and then add 1 to it (incrementing count). The flow loops back to the decision step to check again.

     • If the answer is No: We exit the process and reach the end of the flowchart.

Common Flowchart Patterns

• Counter Loops: Repeat processes a fixed number of times.

• Conditional Branching: Handle decisions diverging based on conditions (true/false, if-else).

• Accumulators: Collect values, often used in loops for cumulative calculations.

Practice Interpreting Flowcharts

• Example Question: Analyzing a flowchart that checks if a number is greater than 10. Outputs a message based on the input.

• Answer: (Flowchart)

  • Start

  • Input: number

  • Decision: number > 10

    • Yes: Print “Greater than 10”

    • No: Print “10 or Less”

  • End

Tips for Drawing Flowcharts

• Define the Goal: Clearly specify the program's objectives.

• Choose Symbols Carefully: Proper usage of symbols aids clarity.

• Use Arrows for Flow Direction: Maintain visibility of operational paths.

• Keep It Simple: Avoid unnecessary complexity in designs.

• Label Decisions: Clearly mark paths (Yes/No, True/False).

Summary

• Flowcharts are a crucial tool for visualizing programming logic, enhancing understanding of algorithms. Practicing flowchart creation bolsters problem-solving skills and logical programming approaches.