Fundamentals of Python Chapter 2

Fundamentals of Python: First Programs

• This is a second edition textbook
• Chapter 2 covers software development, data types, and expressions

Objectives

• 2.1: Describe the basic phases of software development: analysis, design, coding, and testing
• 2.2: Use strings for terminal input and output of text.
• 2.3: Use integers and floating-point numbers in arithmetic operations.
• 2.4: Construct arithmetic expressions
• 2.5: Initialize and use variables with appropriate names.
• 2.6: Import functions from library modules.
• 2.7: Call functions with arguments and use returned values appropriately.
• 2.8: Construct a simple Python program that performs inputs, calculations, and outputs.
• 2.9: Use docstrings to document Python programs.

The Software Development Process

• Software development is a process of planning and organizing a program.

• A common approach is the waterfall model.

• Waterfall phases: Customer request, Analysis, Design, Implementation, Integration, and Maintenance.

• Software development is usually incremental and iterative.

• Initial phases of analysis and design may produce a prototype before fully implementing the solution in more detail.

• Testing is crucial as programs rarely work perfectly the first time and the cost of fixing defects is not uniform across the phases. (analysis and design are cheap; integration and maintenance are expensive)

• Figure 2-1 shows the waterfall model diagrammatically.

• Figure 2-2 displays the relative cost associated with correcting faults, illustrating that errors found during the maintenance phase are more expensive to resolve.

• Figure 2-3 visually represents the percentage distribution of total cost throughout each phase of development

Strings, Assignment, and Comments

• Text processing is a common computer application.
• Email, text messages, web pages, and word processing depend on strings of characters.

Data Types

• A data type defines a set of values and operations.
• A literal is the way a data value is written to a programmer.
• Integers and Floats represent numerical data.
• Figure 2-10 lists integer, real, and character string data types with example literals

String Literals

• Python strings are enclosed by single or double quotes.
• Empty strings are represented by "" or "".
• Double quotes are preferable if the string contains single quotes or apostrophes.
• Triple quotes can be used to span multiple lines.

Escape Sequences

• Escape sequences control special characters in strings (e.g., newline \n, tab \t, backslash \, single quote ', double quote " etc).
• Each sequence is associated with a meaning as shown in the table.

String Concatenation

• The '+' operator joins strings.
• The '*' operator repeats string inputs.

Variables and the Assignment Statement

• Variables associate a name with a value.
• Variable names must follow specific rules (e.g., no reserved keywords, start with letter or _, case sensitivity)
• Programmers frequently use uppercase for symbolic constants (e.g. TAX_RATE).
• Variables usually hold data values that change.
• The assignment statement stores a value into a variable.

Program Comments and Docstrings

• Program comments are ignored by the computer but provide documentation for programmers.
• Docstrings are multiline string comments that outline program purpose and usage.
• End-of-line comments begin with a '#' symbol.

Numeric Data Types and Character Sets

• Computers often crunch numbers in applications.
• Python uses floating-point numbers to represent reals.

Integers

• Integers have infinite range in real life.
• Computers limit integer magnitude; ranges are dependent on the programming language (Python's int range is -2,131,483,648 to +2,147,483,647 or so.)
• Integer literals are written using digits without commas.

Floating-Point Numbers

• Real numbers have infinite precision
• Floating-point numbers are used to represent real numbers.
• Python's float range is -1.8e308 to 1.8e308 or so
• Floating and decimal numbers can be represented using decimal or scientific notation.

Character Sets

• Character literals are similar to strings but can be included in different character sets such as ASCII and Unicode.
• ASCII maps chars and integers
• Ord and chr functions are used for conversions.

Expressions

• Literals evaluate to themselves.
• Variables evaluate to their values.
• Expressions combine operands and operators and follow precedence rules, using parenthesis for complex evaluations.

Arithmetic Expressions

• Arithmetic expressions involve operands (values) and operators (like +, -, *, /).

• Precedence rules govern operator evaluation order.

• The same numeric types yield the same resultant type.

• Mixed-mode operations take on the type of the more inclusive numeric set (float > int in resultant values)

• Line continuation needs the backslash ('') character.

Mixed-Mode Arithmetic and Type Conversions.

• Mixed-mode arithmetic involves integers and floating-point numbers.
• Type conversion functions (int and float) convert strings to numbers before arithmetic.

Using Functions and Modules

• Python libraries called modules organize functions.

Calling Functions: Arguments and Return Values

• Functions include arguments (sometimes optional) for input.
• Some functions return a value back to the part of the program that called them.

The Math Module

• Modules contain functions for various tasks (e.g., mathematical functions like sqrt, pi)
• To use a resource from a module, put the module name preceding a resource name connected via a dot character('.')
• From the module, you can import resources to avoid using qualifiers

The Main Module

• A Python program often has a main module that can be imported by other modules.

Program Format and Structure

• Programs generally begin with documentation comments with author's name, program description, use cases, or other helpful information.
• Then imports are made, input and variable initialization occurs, followed by a process section determining output, and lastly output results section from the program.

Chapter Summary

• The waterfall model describes software development in discrete phases.
• Literals represent data values within a program.
• String type is for text.
• Escape characters begin with a backslash ().
• Comments are meant to aid programmers (code that is ignored by the Python interpreter).
• Variables hold values that can change.
• Typical data types are int and float.
• The order of operator evaluation, like the math rules, is called precedence.
• Mixed-mode arithmetic involves different numeric types.
• Converting values from one type to another is called type conversion.
• Functions and modules structure Python programs. Functions are groups of code (modules bring together functions and other resources.

This quiz on Chapter 2 of the 'Fundamentals of Python' textbook delves into essential concepts of software development, data types, and expressions. It covers various objectives related to variable initialization, arithmetic operations, and the use of functions. Test your understanding of these foundational programming topics.