Book: The Python Language Reference Manual

Overview

The Python Language Reference Manual from 2003 by Guido van Rossum provides an authoritative, precise description of the Python language as it stood in the early 2000s. It serves as the definitive specification for syntax, semantics, and the core behaviors programmers and implementers rely on. The manual emphasizes clarity and formality so that readers can understand exactly how Python constructs behave and how implementations should conform.

Lexical structure and syntax

The manual opens with the lexical structure of the language, defining tokens, identifiers, keywords, literals, operators, and the rules for whitespace and indentation that make Python distinctive. It presents a formal grammar and explains how source code is parsed into the syntactic building blocks used by the interpreter. Attention is given to lexical quirks such as string literal forms, escape sequences, and the significance of line breaks and indentation in delimiting blocks.

Built-in types and object model

A central portion of the manual describes the core built-in types: numbers, sequences (strings, lists, tuples), mappings (dictionaries), sets, and other data structures. Each type is specified in terms of its operations, behaviors, and semantics, including mutability, indexing, slicing, and iteration. The language's object model is explained in terms of objects, references, names, and attribute access, clarifying identity, equivalence, and the role of built-in functions that manipulate objects.

Statements, expressions, and control flow

Detailed sections cover the full range of statements and expressions: assignments, augmented assignments, conditionals, loops, comprehensions, import semantics, and control-flow statements such as break, continue, and return. Expression evaluation order and operator precedence are laid out precisely so that the interaction of complex expressions is unambiguous. The manual defines evaluation semantics so that both programmers and implementers know how values are produced and propagated.

Functions, modules, and namespaces

Function definition and invocation receive careful treatment, including parameter passing conventions, default and keyword arguments, variable-length argument lists, and scoping rules. The manual explains local, global, and built-in namespaces and the rules governing name resolution. Module import semantics, package layout, and the lifecycle of modules are specified to make module-level behavior predictable across different execution environments.

Classes, exceptions, and inheritance

Object-oriented features are described in precise terms: class definition, instance creation, attribute lookup, method invocation, and the method resolution order used for inheritance. The exception model is specified, covering how exceptions are raised, propagated, caught, and how finally and else clauses interact with exception handling. The manual clarifies how custom exception types integrate with the language and how resource cleanup is performed.

Runtime, implementation notes, and conformance

The manual addresses runtime considerations such as the execution model, import mechanisms, and the interaction of the interpreter with the operating environment. It outlines the standard behaviors that Python implementations should provide, notes implementation-defined details, and points to the library documentation for facilities outside the core language. Conformance guidance helps implementers and tool authors ensure compatibility and portability across different interpreters.

Utility as a reference

Designed for language users, library authors, and implementers, the manual functions as a formal reference rather than a tutorial. It is most valuable when precise, unambiguous answers about language behavior are required, supporting correct program construction, debugging, and language implementation efforts. The 2003 edition captures the language's essential rules and idioms, making it a foundational resource for understanding Python's semantics.