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Python/compile.c (part 2)

cpython 3.14 @ ab2d84fe1023/Python/compile.c

This annotation covers comprehension scoping, class compilation, the walrus operator, and match/case (structural pattern matching) in Python/compile.c. For the function call compilation, import, and exception handling see the python_compile_c annotation.

Map​

LinesSymbolRole
1-500Comprehension compilerNested compiler unit, iter argument injection
501-900Class body compiler__class__ cell, __build_class__, __classcell__
901-1300Augmented assignmentLOAD_/STORE_ pair with in-place binary op
1301-1600Walrus operator :=COPY + assignment in comprehension scope
1601-3000match/casePattern matching: wildcard, capture, class, or, guard

Reading​

Comprehension as nested function​

Every list/set/dict comprehension and generator expression compiles into a nested function. The outermost iterable is passed as the first argument (.0); inner iterables are re-evaluated in the nested scope. This nested function is called immediately for list/set/dict comprehensions and returned as a generator for generator expressions.

// CPython: Python/compile.c:1142 compiler_comprehension
static int
compiler_comprehension(struct compiler *c, expr_ty e, int type,
                       identifier name, asdl_seq *generators, expr_ty elt, ...)
{
    ...
    if (compiler_enter_scope(c, name, COMPILER_SCOPE_COMPREHENSION, ...) < 0)
        return ERROR;
    ...
}

__class__ cell for super()​

When a method body references super() with no arguments, the compiler implicitly adds a __class__ cell variable that holds the defining class. LOAD_CLOSURE at the end of the class body captures it for the methods.

match/case compilation​

Structural pattern matching compiles to a decision tree of MATCH_CLASS, MATCH_MAPPING, MATCH_SEQUENCE, and IS_OP/CONTAINS_OP checks. Each pattern test either falls through to the pattern body or jumps to the next case. Guard expressions are compiled after the structural match succeeds.

Walrus operator in comprehensions​

:= inside a comprehension assigns to the enclosing scope, not the comprehension's nested scope. The compiler uses COPY (duplicate stack top) to both use the value in the comprehension and store it in the outer frame.

gopy notes​

compile/codegen_expr.go handles comprehensions. compile/codegen_class.go handles class body compilation including the __class__ cell. match/case is partially implemented in compile/codegen_stmt.go.