Python Fundamentals

A practical guide for learning Python, complete with real-world projects for you to explore

Ryan Marvin, Mark Ng'ang'a, and Amos Omondi

Python Fundamentals

Copyright © 2018 Packt Publishing

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Authors: Ryan Marvin, Mark Ng'ang'a, and Amos Omondi

Managing Editor: Taabish Khan

Acquisitions Editor: Koushik Sen

Production Editor: Nitesh Thakur

Editorial Board: David Barnes, Ewan Buckingham, Simon Cox, Manasa Kumar, Alex Mazonowicz, Douglas Paterson, Dominic Pereira, Shiny Poojary, Saman Siddiqui, Erol Staveley, Ankita Thakur, and Mohita Vyas

First Published: October 2018

Production Reference: 1311018

ISBN: 978-1-78980-732-5

Table of Contents

Preface   i

Introducing Python   1

Introduction   2

Python 2 Versus Python 3   2

Working with the Python Interactive Shell   3

Exercise 1: Checking our Python Installation   3

Exercise 2: Working with the Python Interpreter   4

Activity 1: Working with the Python Shell   5

Writing and Running Simple Scripts   5

Exercise 3: Creating a Script   6

Running a File Containing Invalid Commands   8

Exercise 4: Passing User Arguments to Scripts   9

Activity 2: Running Simple Python Scripts   10

Python Syntax   12

Variables   12

Values   12

Exercise 5: Checking the Type of a Value   13

Type Conversion   14

Exercise 6: Assigning Variables   15

Exercise 7: Using Variables   16

Multiple Assignment   19

Activity 3: Using Variables and Assign Statements   20

Naming Identifiers and Reserved Words   21

Exercise 8: Python Keywords   23

Python Naming Conventions   24

Activity 4: Variable Assignment and Variable Naming Conventions   26

User Input, Comments, and Indentations   28

User Input from the Keyboard   28

Passing in a Prompt to the input Function   28

Using Different Input Data Types in your Program   29

Exercise 9: Fetching and Using User Input   29

Comments   30

Indentation   32

Exercise 10: The Importance of Proper Indentation   33

Activity 5: Fixing Indentations in a Code Block   35

Activity 6: Implementing User Input and Comments in a Script   36

Summary   37

Data Types   39

Introduction   40

Numerical Data   40

Types of Numbers   40

Exercise 11: Converting Between Different Types of Number Systems   43

Operators   44

Order of Operations   48

Activity 7: Order of Operations   49

Activity 8: Using Different Arithmetic Operators   50

Strings   51

String Operations and Methods   51

Indexing   53

Slicing   54

Activity 9: String Slicing   55

Length   56

String Formatting   56

String Methods   58

Activity 10: Working with Strings   61

Escape Sequences   62

Exercise 12: Using Escape Sequences   64

Activity 11: Manipulating Strings   65

Lists   66

List Operations   67

Exercise 13: List References   70

Activity 12: Working with Lists   71

Booleans   72

Comparison Operators   73

Logical Operators   74

Membership Operators   75

Activity 13: Using Boolean Operators   76

Summary   77

Control Statements   79

Introduction   80

Control Statements   80

Program Flow   80

Control Statement   81

The if Statement   82

Exercise 14: Using the if Statement   82

Activity 14: Working with the if Statement   84

The while Statement   85

Exercise 15: Using the while Statement   86

Exercise 16: Using while to Keep a Program Running   88

Activity 15: Working with the while Statement   90

while Versus if   91

Loops   92

The for Loop   92

Exercise 17: Using the for Loop   93

Using else   94

The range Function   96

Activity 16: The for loop and the range Function   99

Nesting Loops   99

Exercise 18: Using Nested Loops   100

Activity 17: Nested Loops   101

Breaking Out of Loops   103

The break Statement   103

The continue Statement   104

The pass Statement   105

Activity 18: Breaking out of Loops   106

Summary   108

Functions   111

Introduction   112

Built-In Functions   112

User-Defined Functions   113

Calling a Function   114

Global and Local Variables   114

Exercise 19: Defining Global and Local Variables   115

Function Return   117

Using main()   118

Function Arguments   119

Required Arguments   120

Keyword Arguments   120

Default Arguments   121

Variable Number of Arguments   122

Activity 19: Function Arguments   122

Anonymous Functions   123

Exercise 20: Creating a Lambda Function   123

Activity 20: Using Lambda Functions   125

Summary   126

Lists and Tuples   129

Introduction   130

List Syntax   130

List Methods   131

list.append(item)   132

list.extend(iterable)   132

list.insert(index, item)   133

list.remove(item)   134

list.pop([index])   135

list.clear()   135

list.index(item [, start [, end]])   136

list.count(item)   137

list.sort(key=None, reverse=False)   137

list.reverse()   137

list.copy()   138

Activity 21: Using the List Methods   138

List Comprehensions   138

Tuple Syntax   140

Exercise 21: Creating a Tuple   142

Accessing Tuple Elements   143

Indexing   143

Exercise 22: Accessing Tuple Elements Using Indexing   143

Slicing   145

Exercise 21: Creating a Tuple   145

Accessing Tuple Elements   146

Indexing   146

Exercise 23: Accessing Tuple Elements Using Slicing   146

Tuple Methods   148

Activity 22: Using Tuple Methods   149

Summary   149

Dictionaries and Sets   151

Introduction   152

Working with Dictionaries   152

Activity 23: Creating a Dictionary   153

Exercise 24: Adding Data to a Dictionary   154

Exercise 25: Reading Data from a Dictionary   155

Exercise 26: Iterating Through Dictionaries   155

Checking for the Existence of Particular Keys   157

Additional Dictionary Attributes   158

dict.update()   158

dict.clear() and dict.pop()   159

dict.copy()   160

dict.popitem()   161

dict.setdefault()   161

dict.fromkeys()   162

Activity 24: Arranging and Presenting Data Using Dictionaries   163

Ordered Dictionaries   164

Activity 25: Combining Dictionaries   165

The Basics of Sets   166

Exercise 27: Creating Sets   166

Exercise 28: Adding Data to a Set   168

Exercise 29: Reading Data from a Set   168

Activity 26: Building a Set   169

Exercise 30: Removing Data from a Set   170

Set Operations   171

Union   171

Intersection   172

Difference   173

Subsets   174

Equality   175

Update Methods   175

Frozen Sets   176

Activity 27: Creating Unions of Elements in a Collection   177

Summary   177

Object-Oriented Programming   179

Introduction   180

A First Look at OOP   180

OOP in Python   181

Defining a Class in Python   182

Exercise 31: Creating a Class   182

Instantiating an Object   183

Exercise 32: Instantiating a Person Object   183

Adding Attributes to an Object   184

The __init__ Method   185

Exercise 33: Adding Attributes to a Class   186

Activity 28: Defining a Class and Objects   187

Methods in a Class   188

Defining Methods in a Class   188

Exercise 34: Creating a Method for our Class   189

Passing Arguments to Instance Methods   190

Exercise 35: Passing Arguments to Instance Methods   190

Exercise 36: Setting Instance Attributes within Instance Methods   192

Activity 29: Defining Methods in a Class   193

Class Versus Instance Attributes   194

Exercise 37: Declaring a Class with Instance Attributes   195

Class Attributes   196

Exercise 38: Extending our Class with Class Attributes   196

Exercise 39: Implementing a Counter for Instances of a Class   198

Activity 30: Creating Class Attributes   199

Class Versus Instance Methods   200

Exercise 40: Creating Instance Methods   200

Class Methods   202

Exercise 41: Testing our Factory Method   204

Exercise 42: Accessing Class Attributes from within Class Methods   205

Encapsulation and Information Hiding   207

Activity 31: Creating Class Methods and Using Information Hiding   210

Class Inheritance   212

Exercise 43: Implementing Class Inheritance   213

Overriding __init__()   217

Exercise 44: Overriding the __init__ Method to Add an Attribute   218

Commonly Overridden Methods   220

Activity 32: Overriding Methods   222

Multiple Inheritance   223

Exercise 45: Implementing Multiple Inheritance   224

Activity 33: Practicing Multiple Inheritance   225

Summary   226

Modules, Packages, and File Operations   229

Introduction   230

Defining Modules   231

Exercise 46: Creating Modules   232

Imports and Import Statements   233

Exercise 47: Importing Modules   234

Modules and Packages   235

The Module Search Path   235

Standard Python Modules   235

Activity 34: Inspecting Modules   238

Packages   238

Absolute Imports   239

Relative Imports   239

Activity 35: Listing the Resources Defined in a Package or Module   240

Activity 36: Using Resources in a Module   241

File Operations   242

The file Object   242

The file Object Methods   242

Reading and Writing to Files   243

The open() Method   243

Exercise 48: Creating, Reading, and Writing to Files   244

The with Context Manager   246

Activity 37: Performing File Operations   247

Handling Structured Data   247

Working with CSV Data   249

Activity 38: Working with Files   252

Working with JSON Data   253

Summary   255

Error Handling   257

Introduction   258

Errors and Exceptions in Python   258

How to Raise Exceptions   259

Built-In Exceptions   259

SyntaxError   260

ImportError   260

KeyError   261

TypeError   262

AttributeError   262

IndexError   263

NameError   263

FileNotFoundError   264

Activity 39: Identifying Error Scenarios   264

Handling Errors and Exceptions   265

Exercise 49: Implementing the try…except Block   266

Exercise 50: Implementing the try…except…else Block   268

Exercise 51: Implementing the finally Keyword   269

Activity 40: Handling Errors   270

Custom Exceptions   270

Implementing Your Own Exception Class   271

Activity 41: Creating Your Own Custom Exception Class   271

Summary   272

Appendix A   275