Fluent Python: Clear, Concise, and Effective Programming. 2 Ed

Cover....1 Copyright....4 Table of Contents....7 Preface....21 Who This Book Is For....22 Who This Book Is Not For....22 Five Books in One....22 How the Book Is Organized....23 Hands-On Approach....24 Soapbox: My Personal Perspective....25 Companion Website: fluentpython.com....25 Conventions Used in This Book....25 Using Code Examples....26 O’Reilly Online Learning....27 How to Contact Us....27 Acknowledgments....27 Acknowledgments for the First Edition....29 Part I. Data Structures....31 Chapter 1. The Python Data Model....33 What’s New in This Chapter....34 A Pythonic Card Deck....35 How Special Methods Are Used....38 Emulating Numeric Types....39 String Representation....42 Boolean Value of a Custom Type....43 Collection API....44 Overview of Special Methods....45 Why len Is Not a Method....47 Chapter Summary....48 Further Reading....48 Chapter 2. An Array of Sequences....51 What’s New in This Chapter....52 Overview of Built-In Sequences....52 List Comprehensions and Generator Expressions....55 List Comprehensions and Readability....55 Listcomps Versus map and filter....57 Cartesian Products....57 Generator Expressions....59 Tuples Are Not Just Immutable Lists....60 Tuples as Records....60 Tuples as Immutable Lists....62 Comparing Tuple and List Methods....64 Unpacking Sequences and Iterables....65 Using * to Grab Excess Items....66 Unpacking with * in Function Calls and Sequence Literals....67 Nested Unpacking....67 Pattern Matching with Sequences....68 Pattern Matching Sequences in an Interpreter....73 Slicing....77 Why Slices and Ranges Exclude the Last Item....77 Slice Objects....78 Multidimensional Slicing and Ellipsis....79 Assigning to Slices....80 Using + and * with Sequences....80 Building Lists of Lists....81 Augmented Assignment with Sequences....83 A += Assignment Puzzler....84 list.sort Versus the sorted Built-In....86 When a List Is Not the Answer....89 Arrays....89 Memory Views....92 NumPy....94 Deques and Other Queues....97 Chapter Summary....100 Further Reading....101 Chapter 3. Dictionaries and Sets....107 What’s New in This Chapter....108 Modern dict Syntax....108 dict Comprehensions....109 Unpacking Mappings....110 Merging Mappings with |....110 Pattern Matching with Mappings....111 Standard API of Mapping Types....113 What Is Hashable....114 Overview of Common Mapping Methods....115 Inserting or Updating Mutable Values....117 Automatic Handling of Missing Keys....120 defaultdict: Another Take on Missing Keys....120 The __missing__ Method....121 Inconsistent Usage of __missing__ in the Standard Library....124 Variations of dict....125 collections.OrderedDict....125 collections.ChainMap....125 collections.Counter....126 shelve.Shelf....127 Subclassing UserDict Instead of dict....127 Immutable Mappings....129 Dictionary Views....131 Practical Consequences of How dict Works....132 Set Theory....133 Set Literals....135 Set Comprehensions....136 Practical Consequences of How Sets Work....137 Set Operations....137 Set Operations on dict Views....140 Chapter Summary....142 Further Reading....143 Chapter 4. Unicode Text Versus Bytes....147 What’s New in This Chapter....148 Character Issues....148 Byte Essentials....150 Basic Encoders/Decoders....153 Understanding Encode/Decode Problems....155 Coping with UnicodeEncodeError....155 Coping with UnicodeDecodeError....156 SyntaxError When Loading Modules with Unexpected Encoding....158 How to Discover the Encoding of a Byte Sequence....158 BOM: A Useful Gremlin....159 Handling Text Files....161 Beware of Encoding Defaults....164 Normalizing Unicode for Reliable Comparisons....170 Case Folding....172 Utility Functions for Normalized Text Matching....173 Extreme “Normalization”: Taking Out Diacritics....174 Sorting Unicode Text....178 Sorting with the Unicode Collation Algorithm....180 The Unicode Database....180 Finding Characters by Name....181 Numeric Meaning of Characters....183 Dual-Mode str and bytes APIs....185 str Versus bytes in Regular Expressions....185 str Versus bytes in os Functions....186 Chapter Summary....187 Further Reading....188 Chapter 5. Data Class Builders....193 What’s New in This Chapter....194 Overview of Data Class Builders....194 Main Features....197 Classic Named Tuples....199 Typed Named Tuples....202 Type Hints 101....203 No Runtime Effect....203 Variable Annotation Syntax....204 The Meaning of Variable Annotations....205 More About @dataclass....209 Field Options....210 Post-init Processing....213 Typed Class Attributes....215 Initialization Variables That Are Not Fields....216 @dataclass Example: Dublin Core Resource Record....217 Data Class as a Code Smell....220 Data Class as Scaffolding....221 Data Class as Intermediate Representation....221 Pattern Matching Class Instances....222 Simple Class Patterns....222 Keyword Class Patterns....223 Positional Class Patterns....224 Chapter Summary....225 Further Reading....226 Chapter 6. Object References, Mutability, and Recycling....231 What’s New in This Chapter....232 Variables Are Not Boxes....232 Identity, Equality, and Aliases....234 Choosing Between == and is....236 The Relative Immutability of Tuples....237 Copies Are Shallow by Default....238 Deep and Shallow Copies of Arbitrary Objects....241 Function Parameters as References....243 Mutable Types as Parameter Defaults: Bad Idea....244 Defensive Programming with Mutable Parameters....246 del and Garbage Collection....249 Tricks Python Plays with Immutables....251 Chapter Summary....253 Further Reading....254 Part II. Functions as Objects....259 Chapter 7. Functions as First-Class Objects....261 What’s New in This Chapter....262 Treating a Function Like an Object....262 Higher-Order Functions....264 Modern Replacements for map, filter, and reduce....265 Anonymous Functions....266 The Nine Flavors of Callable Objects....267 User-Defined Callable Types....269 From Positional to Keyword-Only Parameters....270 Positional-Only Parameters....272 Packages for Functional Programming....273 The operator Module....273 Freezing Arguments with functools.partial....277 Chapter Summary....279 Further Reading....280 Chapter 8. Type Hints in Functions....283 What’s New in This Chapter....284 About Gradual Typing....284 Gradual Typing in Practice....285 Starting with Mypy....286 Making Mypy More Strict....287 A Default Parameter Value....288 Using None as a Default....290 Types Are Defined by Supported Operations....290 Types Usable in Annotations....296 The Any Type....296 Simple Types and Classes....299 Optional and Union Types....300 Generic Collections....301 Tuple Types....304 Generic Mappings....306 Abstract Base Classes....308 Iterable....310 Parameterized Generics and TypeVar....312 Static Protocols....316 Callable....321 NoReturn....324 Annotating Positional Only and Variadic Parameters....325 Imperfect Typing and Strong Testing....326 Chapter Summary....327 Further Reading....328 Chapter 9. Decorators and Closures....333 What’s New in This Chapter....334 Decorators 101....334 When Python Executes Decorators....336 Registration Decorators....338 Variable Scope Rules....338 Closures....341 The nonlocal Declaration....345 Variable Lookup Logic....346 Implementing a Simple Decorator....347 How It Works....348 Decorators in the Standard Library....350 Memoization with functools.cache....350 Using lru_cache....353 Single Dispatch Generic Functions....354 Parameterized Decorators....359 A Parameterized Registration Decorator....359 The Parameterized Clock Decorator....362 A Class-Based Clock Decorator....365 Chapter Summary....366 Further Reading....366 Chapter 10. Design Patterns with First-Class Functions....371 What’s New in This Chapter....372 Case Study: Refactoring Strategy....372 Classic Strategy....372 Function-Oriented Strategy....377 Choosing the Best Strategy: Simple Approach....380 Finding Strategies in a Module....381 Decorator-Enhanced Strategy Pattern....383 The Command Pattern....385 Chapter Summary....387 Further Reading....388 Part III. Classes and Protocols....391 Chapter 11. A Pythonic Object....393 What’s New in This Chapter....394 Object Representations....394 Vector Class Redux....395 An Alternative Constructor....398 classmethod Versus staticmethod....399 Formatted Displays....400 A Hashable Vector2d....404 Supporting Positional Pattern Matching....407 Complete Listing of Vector2d, Version 3....408 Private and “Protected” Attributes in Python....412 Saving Memory with __slots__....414 Simple Measure of __slot__ Savings....417 Summarizing the Issues with __slots__....418 Overriding Class Attributes....419 Chapter Summary....421 Further Reading....422 Chapter 12. Special Methods for Sequences....427 What’s New in This Chapter....428 Vector: A User-Defined Sequence Type....428 Vector Take #1: Vector2d Compatible....429 Protocols and Duck Typing....432 Vector Take #2: A Sliceable Sequence....433 How Slicing Works....434 A Slice-Aware __getitem__....436 Vector Take #3: Dynamic Attribute Access....437 Vector Take #4: Hashing and a Faster ==....441 Vector Take #5: Formatting....448 Chapter Summary....455 Further Reading....456 Chapter 13. Interfaces, Protocols, and ABCs....461 The Typing Map....462 What’s New in This Chapter....463 Two Kinds of Protocols....464 Programming Ducks....465 Python Digs Sequences....466 Monkey Patching: Implementing a Protocol at Runtime....468 Defensive Programming and “Fail Fast”....470 Goose Typing....472 Subclassing an ABC....477 ABCs in the Standard Library....479 Defining and Using an ABC....481 ABC Syntax Details....487 Subclassing an ABC....488 A Virtual Subclass of an ABC....490 Usage of register in Practice....493 Structural Typing with ABCs....494 Static Protocols....496 The Typed double Function....496 Runtime Checkable Static Protocols....498 Limitations of Runtime Protocol Checks....501 Supporting a Static Protocol....502 Designing a Static Protocol....504 Best Practices for Protocol Design....506 Extending a Protocol....507 The numbers ABCs and Numeric Protocols....508 Chapter Summary....511 Further Reading....512 Chapter 14. Inheritance: For Better or for Worse....517 What’s New in This Chapter....518 The super() Function....518 Subclassing Built-In Types Is Tricky....520 Multiple Inheritance and Method Resolution Order....524 Mixin Classes....530 Case-Insensitive Mappings....530 Multiple Inheritance in the Real World....532 ABCs Are Mixins Too....532 ThreadingMixIn and ForkingMixIn....533 Django Generic Views Mixins....534 Multiple Inheritance in Tkinter....537 Coping with Inheritance....540 Favor Object Composition over Class Inheritance....540 Understand Why Inheritance Is Used in Each Case....540 Make Interfaces Explicit with ABCs....541 Use Explicit Mixins for Code Reuse....541 Provide Aggregate Classes to Users....541 Subclass Only Classes Designed for Subclassing....542 Avoid Subclassing from Concrete Classes....543 Tkinter: The Good, the Bad, and the Ugly....543 Chapter Summary....544 Further Reading....545 Chapter 15. More About Type Hints....549 What’s New in This Chapter....549 Overloaded Signatures....550 Max Overload....551 Takeaways from Overloading max....555 TypedDict....556 Type Casting....564 Reading Type Hints at Runtime....567 Problems with Annotations at Runtime....568 Dealing with the Problem....570 Implementing a Generic Class....571 Basic Jargon for Generic Types....574 Variance....574 An Invariant Dispenser....575 A Covariant Dispenser....576 A Contravariant Trash Can....577 Variance Review....579 Implementing a Generic Static Protocol....582 Chapter Summary....584 Further Reading....585 Chapter 16. Operator Overloading....591 What’s New in This Chapter....592 Operator Overloading 101....592 Unary Operators....593 Overloading + for Vector Addition....596 Overloading * for Scalar Multiplication....602 Using @ as an Infix Operator....604 Wrapping-Up Arithmetic Operators....606 Rich Comparison Operators....607 Augmented Assignment Operators....610 Chapter Summary....615 Further Reading....617 Part IV. Control Flow....621 Chapter 17. Iterators, Generators, and Classic Coroutines....623 What’s New in This Chapter....624 A Sequence of Words....624 Why Sequences Are Iterable: The iter Function....626 Using iter with a Callable....628 Iterables Versus Iterators....629 Sentence Classes with __iter__....633 Sentence Take #2: A Classic Iterator....633 Don’t Make the Iterable an Iterator for Itself....635 Sentence Take #3: A Generator Function....636 How a Generator Works....637 Lazy Sentences....640 Sentence Take #4: Lazy Generator....640 Sentence Take #5: Lazy Generator Expression....641 When to Use Generator Expressions....643 An Arithmetic Progression Generator....645 Arithmetic Progression with itertools....648 Generator Functions in the Standard Library....649 Iterable Reducing Functions....660 Subgenerators with yield from....662 Reinventing chain....663 Traversing a Tree....664 Generic Iterable Types....669 Classic Coroutines....671 Example: Coroutine to Compute a Running Average....673 Returning a Value from a Coroutine....676 Generic Type Hints for Classic Coroutines....680 Chapter Summary....682 Further Reading....682 Chapter 18. with, match, and else Blocks....687 What’s New in This Chapter....688 Context Managers and with Blocks....688 The contextlib Utilities....693 Using @contextmanager....694 Pattern Matching in lis.py: A Case Study....699 Scheme Syntax....699 Imports and Types....701 The Parser....701 The Environment....703 The REPL....705 The Evaluator....706 Procedure: A Class Implementing a Closure....715 Using OR-patterns....716 Do This, Then That: else Blocks Beyond if....717 Chapter Summary....719 Further Reading....720 Chapter 19. Concurrency Models in Python....725 What’s New in This Chapter....726 The Big Picture....726 A Bit of Jargon....727 Processes, Threads, and Python’s Infamous GIL....729 A Concurrent Hello World....731 Spinner with Threads....731 Spinner with Processes....734 Spinner with Coroutines....736 Supervisors Side-by-Side....741 The Real Impact of the GIL....743 Quick Quiz....743 A Homegrown Process Pool....746 Process-Based Solution....748 Understanding the Elapsed Times....748 Code for the Multicore Prime Checker....749 Experimenting with More or Fewer Processes....753 Thread-Based Nonsolution....754 Python in the Multicore World....755 System Administration....756 Data Science....757 Server-Side Web/Mobile Development....758 WSGI Application Servers....760 Distributed Task Queues....762 Chapter Summary....763 Further Reading....764 Concurrency with Threads and Processes....764 The GIL....766 Concurrency Beyond the Standard Library....766 Concurrency and Scalability Beyond Python....768 Chapter 20. Concurrent Executors....773 What’s New in This Chapter....773 Concurrent Web Downloads....774 A Sequential Download Script....776 Downloading with concurrent.futures....779 Where Are the Futures?....781 Launching Processes with concurrent.futures....784 Multicore Prime Checker Redux....785 Experimenting with Executor.map....788 Downloads with Progress Display and Error Handling....792 Error Handling in the flags2 Examples....796 Using futures.as_completed....799 Chapter Summary....802 Further Reading....802 Chapter 21. Asynchronous Programming....805 What’s New in This Chapter....806 A Few Definitions....807 An asyncio Example: Probing Domains....808 Guido’s Trick to Read Asynchronous Code....810 New Concept: Awaitable....811 Downloading with asyncio and HTTPX....812 The Secret of Native Coroutines: Humble Generators....814 The All-or-Nothing Problem....815 Asynchronous Context Managers....816 Enhancing the asyncio Downloader....817 Using asyncio.as_completed and a Thread....818 Throttling Requests with a Semaphore....820 Making Multiple Requests for Each Download....824 Delegating Tasks to Executors....827 Writing asyncio Servers....829 A FastAPI Web Service....830 An asyncio TCP Server....834 Asynchronous Iteration and Asynchronous Iterables....841 Asynchronous Generator Functions....842 Async Comprehensions and Async Generator Expressions....848 async Beyond asyncio: Curio....851 Type Hinting Asynchronous Objects....854 How Async Works and How It Doesn’t....855 Running Circles Around Blocking Calls....855 The Myth of I/O-Bound Systems....856 Avoiding CPU-Bound Traps....856 Chapter Summary....857 Further Reading....858 Part V. Metaprogramming....863 Chapter 22. Dynamic Attributes and Properties....865 What’s New in This Chapter....866 Data Wrangling with Dynamic Attributes....866 Exploring JSON-Like Data with Dynamic Attributes....868 The Invalid Attribute Name Problem....872 Flexible Object Creation with __new__....873 Computed Properties....875 Step 1: Data-Driven Attribute Creation....876 Step 2: Property to Retrieve a Linked Record....878 Step 3: Property Overriding an Existing Attribute....882 Step 4: Bespoke Property Cache....883 Step 5: Caching Properties with functools....885 Using a Property for Attribute Validation....887 LineItem Take #1: Class for an Item in an Order....887 LineItem Take #2: A Validating Property....888 A Proper Look at Properties....890 Properties Override Instance Attributes....891 Property Documentation....894 Coding a Property Factory....895 Handling Attribute Deletion....898 Essential Attributes and Functions for Attribute Handling....899 Special Attributes that Affect Attribute Handling....900 Built-In Functions for Attribute Handling....900 Special Methods for Attribute Handling....901 Chapter Summary....903 Further Reading....903 Chapter 23. Attribute Descriptors....909 What’s New in This Chapter....910 Descriptor Example: Attribute Validation....910 LineItem Take #3: A Simple Descriptor....910 LineItem Take #4: Automatic Naming of Storage Attributes....917 LineItem Take #5: A New Descriptor Type....919 Overriding Versus Nonoverriding Descriptors....922 Overriding Descriptors....924 Overriding Descriptor Without __get__....925 Nonoverriding Descriptor....926 Overwriting a Descriptor in the Class....927 Methods Are Descriptors....928 Descriptor Usage Tips....930 Descriptor Docstring and Overriding Deletion....932 Chapter Summary....933 Further Reading....934 Chapter 24. Class Metaprogramming....937 What’s New in This Chapter....938 Classes as Objects....938 type: The Built-In Class Factory....939 A Class Factory Function....941 Introducing __init_subclass__....944 Why __init_subclass__ Cannot Configure __slots__....951 Enhancing Classes with a Class Decorator....952 What Happens When: Import Time Versus Runtime....955 Evaluation Time Experiments....956 Metaclasses 101....961 How a Metaclass Customizes a Class....963 A Nice Metaclass Example....964 Metaclass Evaluation Time Experiment....967 A Metaclass Solution for Checked....972 Metaclasses in the Real World....977 Modern Features Simplify or Replace Metaclasses....977 Metaclasses Are Stable Language Features....978 A Class Can Only Have One Metaclass....978 Metaclasses Should Be Implementation Details....979 A Metaclass Hack with __prepare__....980 Wrapping Up....982 Chapter Summary....983 Further Reading....984 Afterword....989 Further Reading....990 Index....993 About the Author....1010 Colophon....1010