Chapter 2: Input, Processing, and Output - Program Development & Python Basics

Program Development Cycle

• Steps: Talk to the user, design the program, write the code, correct syntax errors, test the program, correct logic errors.

• Talk to the User: Paramount for project success; ensures user needs are met. Often involves different roles (e.g., data analyst, developer, marketer).

• Design the Program: Uses tools like flowcharts (e.g., Lucidchart) and pseudocode.

• Write the Code: Requires a clear understanding of user requirements; otherwise, "Garbage In, Garbage Out" (GIGO).

• Correct Syntax Errors: AI tools can assist, but do not assume AI is always perfect or provides the most efficient solution.

• Test the Program: Verify program output with provided test data. A running program is not necessarily a correct one.

• Correct Logic Errors: Program runs without crashing but produces incorrect results. Examples include using a wrong variable, incorrect indentation (critical in Python loops/conditionals), or incorrect order of mathematical operations (missing parentheses).

Python Best Practices

• Comments: Crucial for code clarity and maintainability.

  • Provide an initial comment explaining the program's overall purpose.

  • List and initialize variables, explicitly defining their data types (e.g., $price = 0.0$ for float, $price = 0$ for integer).

• Avoid Magic Numbers: Do not embed unexplained numerical constants directly into calculations (e.g., $tax_amount = price * 0.1$). Instead, assign them to descriptive variables (e.g., $TAX_PERCENT = 0.1$).

• User Input: Prompt the user to enter values.

  • Use $variable = float(input(\'Enter the prompt:\'))$ or $variable = int(input(\'Enter the prompt:\'))$ to ensure input is stored as a numeric data type (float or integer, respectively) and not as a string.

Output Formatting

• Two Decimal Places: Use the $format()$ function within $print()$ to specify decimal precision.

  • Syntax: $print(\'The amount is: \', format(variable, \".2f\"))$.

  • The string \".2f\" formats the number to a fixed-point notation with exactly two digits after the decimal point.

Homework Assignment (Due Monday)

• Task: Develop a program to calculate a company's annual profit, which is typically $23\%$ of total sales.

• Deliverables (compiled onto a single Word document):

  1. Flowchart (created using Lucidchart).

  2. Pseudocode.

  3. Actual Python Code.

  4. Program Output (using specified test data).

• Specific Requirements:

  • NO Magic Numbers: Define the $23\%$ profit rate as a named variable.

  • User Input: Prompt the user to enter the projected amount of total sales.

  • Output Formatting: Format the calculated profit to two decimal places.

  • Test Data: Use total sales of $257.68$.

  • Output Content: Display ONLY the calculated profit. Do NOT add the profit back to the sales total for the final display. Adjust output strings to clearly state "The profit is:".

Binary/Base 10 Conversion (Reference, related to previous homework)

• Binary String to Base 10 Integer: $x = int(\'1101\', 2)$

• Base 10 Integer to Binary String: $z = bin(43)$ (Output string includes an $OB$ prefix, standing for Output Binary).