Pydon'ts: Write elegant Python code

Foreword....12

Pydon’t disrespect the Zen of Python....13

Zen of Python....14

References....15

Zip up....16

Introduction....16

How zip works....17

Zip is lazy....18

Three is a crowd....19

Mismatched lengths....19

Create a dictionary with zip....20

Examples in code....20

Conclusion....23

References....24

Enumerate me....25

Introduction....25

How enumerate works....26

Optional start argument....27

Unpacking when iterating....27

Examples in code....29

Conclusion....34

References....35

Chaining comparison operators....36

Introduction....37

Chaining of comparison operators....37

Pitfalls....38

Ugly chains....39

Examples in code....40

Conclusion....41

References....41

Boolean short-circuiting....42

Introduction....42

Return values of the and and or operators....43

Short-circuiting....44

Short-circuiting in plain English....46

all and any....47

Short-circuiting in chained comparisons....47

Examples in code....47

Conclusion....56

References....56

set and frozenset....58

Introduction....58

(Mathematical) sets....59

(Common) Operations on sets....60

Differences between set and frozenset....63

What are sets used for?....65

Examples in code....66

Conclusion....70

References....70

List comprehensions 101....71

Introduction....71

What is a list comprehension?....72

A loop that builds a list....72

Filtering data in a list comprehension....74

List comprehensions from first principles....76

Full anatomy of a list comprehension....77

Advantages of list comprehensions....80

Examples in code....81

Conclusion....85

References....85

Sequence indexing....86

Introduction....86

Sequence indexing....87

Maximum legal index and index errors....88

Negative indices....88

Indexing idioms....90

To index or not to index?....90

Best practices in code....91

Conclusion....94

Idiomatic sequence slicing....96

Introduction....96

Slicing syntax....97

What to slice?....98

Slicing from the beginning....99

Slicing until the end....100

Slicing with negative indices....100

Slicing and range....101

Idiomatic slicing patterns....102

Empty slices....103

More empty slices....104

Examples in code....104

Conclusion....107

References....108

String formatting comparison....109

Introduction....109

String formatting rationale....110

Three string formatting methods....111

Value conversion....112

Alignment....113

Named placeholders....114

Accessing nested data structures....114

Parametrised formatting....115

Custom formatting....116

Examples in code....117

Conclusion....118

References....119

Truthy, Falsy, and bool....120

“Truthy” and “Falsy”....122

The __bool__ dunder method....123

Remarks....124

Examples in code....125

Conclusion....128

References....128

Assignment expressions and the walrus operator :=....129

Walrus operator and assignment expressions....129

Examples in code....130

Conclusion....133

References....133

String translate and maketrans methods....134

Introduction....134

str.translate....135

Non-equivalence to str.replace....137

Generic translation tables....138

str.maketrans....139

Examples in code....141

Conclusion....145

References....146

Conditional expressions....147

Introduction....147

What is a conditional expression?....148

Rationale....150

Short-circuiting....151

Conditional expressions and if statements....153

Precedence....156

Conditional expressions that evaluate to Booleans....157

Examples in code....158

Conclusion....159

References....160

Dunder methods....161

Introduction....161

What are dunder methods?....162

List of dunder methods and their interactions....164

Exploring a dunder method....167

Conclusion....169

References....170

Overloading arithmetic operators with dunder methods....171

Introduction....173

The example we will be using....174

Your first arithmetic dunder method....174

The dunder methods for the unary arithmetic operations....176

The dunder methods for binary arithmetic operations....179

Addition and the dunder method __add__....179

Adding validation to your dunder methods....180

Using NotImplemented to flag operations you don’t support....181

Extending your dunder method to more types....183

Reflected dunder methods....185

Implementing reflected dunder methods....185

Augmented arithmetic assignment....190

Full implementation of all arithmetic dunder methods....191

Exercises....216

Conclusion....216

References....217

str and repr....218

str and repr....220

The __str__ and __repr__ dunder methods....220

Examples in code....221

Conclusion....223

References....223

Deep unpacking....224

Introduction....224

Assignments....225

Examples in code....227

Conclusion....229

References....229

Unpacking with starred assignments....231

Starred Assignment....232

Examples in code....233

References....235

Structural pattern matching tutorial....236

Introduction....237

Structural pattern matching Python could already do....237

Your first match statement....237

Pattern matching the basic structure....238

Matching the structure of objects....240

__match_args__....241

Wildcards....242

Naming sub-patterns....244

Traversing recursive structures....245

Conclusion....247

References....247

Structural pattern matching anti-patterns....249

Introduction....250

There should be only one obvious way to do it....250

A short and sweet if statement....250

Be smart(er)....251

Basic mappings....252

Conclusion....257

References....258

Mastering sequence slicing....259

Introduction....259

Slicing step....260

Sequence copying....267

Manipulating mutable sequences....267

More idiomatic slicing....270

Conclusion....273

References....274

Inner workings of sequence slicing....275

Introduction....276

The slice class....276

Getting items from sequences....278

Setting items, deleting items, and container emulation....279

Comma-separated indices and slices....279

Examples in code....280

Conclusion....284

References....284

Properties....286

Introduction....286

What is a property?....287

Common property use cases....289

Properties with setters....293

Property deleters....295

The property descriptor....297

Conclusion....299

References....299

Describing Descriptors....300

Introduction....301

The problem that descriptors solve....301

Your first descriptor....302

Accessing the name of the original attribute....306

Descriptor exercises....309

Descriptor protocol....311

The dunder method __set__....311

Accessing the descriptor objects....315

Built-in descriptors....317

Methods and descriptors....326

Data and non-data descriptors....329

Complete descriptor example: attribute validation....333

Descriptors in the standard library....334

Conclusion....335

References....335

Boost your productivity with the REPL....337

Introduction....337

REPL....338

Just fire up the REPL....338

REPL mechanics....338

The last result....342

Getting help from within the REPL....343

Tips for quick hacks....344

Other tools....346

Conclusion....347

References....347

The power of reduce....348

Introduction....348

How reduce works....349

The rabbit hole of the built-in reductions....350

Why bother?....351

Far-fetched reductions....351

The identity element…....353

Why some people dislike reduce....355

Examples in code....355

Conclusion....357

References....357

Usages of underscore....359

Introduction....359

Recovering last result in the session....360

Prefixes and suffixes for variable names....361

Underscore as a sink....367

Matching everything in the new match statement....369

String localisation....370

Improve number readability....371

Conclusion....372

References....372

name dunder attribute....374

Introduction....374

What is __name__?....375

The module attribute __name__....375

__name__ as an object type attribute....377

Examples in code....379

Conclusion....383

References....383

Pass-by-value, reference, and assignment....384

Introduction....386

Is Python pass-by-value?....386

Is Python pass-by-reference?....387

Python object model....388

Python is pass-by-assignment....392

Making copies....393

Examples in code....396

Conclusion....400

References....400

Watch out for recursion....401

Introduction....402

Watch out for recursion....402

Examples in code....405

Conclusion....411

References....412

EAFP and LBYL coding styles....413

EAFP and LBYL....413

EAFP instead of LBYL?....414

Conclusion....418

References....418

Bite-sized refactoring....419

Introduction....419

Refactoring....420

What to refactor?....421

Case study....421

Conclusion....428

References....429

Naming matters....430

Introduction....430

Naming conventions....431

PEP 8 recommendations....431

Standard names....433

Verbosity....434

Picking a name....437

Context is key....439

Practical example....439

Conclusion....441

References....442

Does elegance matter?....443

Introduction....443

Beware, opinions ahead....444

Elegance is not a dispensable luxury....444

Don’t write that, that’s unreadable....444

The right tool for the job....445

Optimise for rewrite....446

Conclusion....446

References....447

Code style matters....448

Introduction....449

Code style....449

Tools for your tool belt....450

Conclusion....453

References....453

Why mastering Python is impossible, and why that’s ok....455

Introduction....456

“to master”, verb....456

How to get as close to mastering Python as possible....457

Anecdote with string methods....461

Conclusion....462

References....462

Closing thoughts....463

Python has so many libraries that people often forget to take their time to learn about all the really interesting and useful features that Python offers.The Pydon'ts teach you these core features of Python, with plenty of code examples to show you how these features are used in real code in the real world.Want to master Python? Start here?