Pattern Matching Branch Review

Doc/library/dis.rst

@@ -751,6 +751,30 @@ iterations of the loop.
    .. versionadded:: 3.2
 
 
+.. opcode:: GET_LEN
+
+   Push ``len(TOS)`` onto the stack.
+
+   .. versionadded:: 3.10
+
+
+.. opcode:: MATCH_MAPPING
+
+   If TOS is an instance of :class:`collections.abc.Mapping`, push ``True`` onto
+   the stack.  Otherwise, push ``False``.
+
+   .. versionadded:: 3.10
+
+
+.. opcode:: MATCH_SEQUENCE
+
+   If TOS is an instance of :class:`collections.abc.Sequence`, is not an
+   instance of :class:`str`/:class:`bytes`/:class:`bytearray`, and is not an
+   :term:`iterator`, push ``True`` onto the stack.  Otherwise, push ``False``.
+
+   .. versionadded:: 3.10
+
+
 All of the following opcodes use their arguments.
 
 .. opcode:: STORE_NAME (namei)
@@ -1189,6 +1213,55 @@ All of the following opcodes use their arguments.
    .. versionadded:: 3.6
 
 
+.. opcode:: GET_INDEX (i)
+
+   TOS is a sequence.  Push ``TOS[i]`` onto the stack.
+
+   .. versionadded:: 3.10
+
+
+.. opcode:: GET_INDEX_END (i)
+
+   TOS is a sequence, and TOS1 is its length.  Push ``TOS[TOS1 - 1 - i]`` onto
+   the stack.
+
+   .. versionadded:: 3.10
+
+
+.. opcode:: GET_INDEX_SLICE (i)
+
+   TOS is a sequence, and TOS1 is its length.  Push a list formed from
+   ``TOS[x:TOS1 - 1 - y]`` onto the stack, where *x* is the low byte of *i* and
+   *y* is the high bytes of *i*.
+
+   .. versionadded:: 3.10
+
+
+.. opcode:: MATCH_CLASS (count)
+
+   TOS is a tuple of keyword attribute names, TOS1 is the class being matched
+   against, and TOS2 is the match subject. *count* is the number of positional
+   sub-patterns.
+
+   If TOS2 is an instance of TOS1 and has the positional and keyword attributes
+   required by *count* and TOS, replace TOS with ``True`` and TOS1 with a tuple
+   of extracted attributes. Otherwise, replace TOS with ``False``.
+
+   .. versionadded:: 3.10
+
+
+.. opcode:: MATCH_KEYS (copy)
+
+   TOS is a tuple of mapping keys, and TOS1 is the match subject.  If TOS1
+   contains all of the keys in TOS, replace TOS with a tuple containing the
+   corresponding values and push ``True``. Otherwise, push ``False``.
+
+   If *copy* is non-zero, gather remaining items into a :class:`dict` and put it
+   on the stack where the subject used to be.
+
+   .. versionadded:: 3.10
+
+
 .. opcode:: HAVE_ARGUMENT
 
    This is not really an opcode.  It identifies the dividing line between

Doc/tools/susp-ignored.csv

@@ -359,3 +359,4 @@ whatsnew/changelog,,::,default::DeprecationWarning
 library/importlib.metadata,,:main,"EntryPoint(name='wheel', value='wheel.cli:main', group='console_scripts')"
 library/importlib.metadata,,`,loading the metadata for packages for the indicated ``context``.
 library/re,,`,"`"
+library/dis,,:TOS1,TOS[x:TOS1 - 1 - y]

Grammar/python.gram

@@ -85,6 +85,7 @@ compound_stmt[stmt_ty]:
     | &('for' | ASYNC) for_stmt
     | &'try' try_stmt
     | &'while' while_stmt
+    | match_stmt
 
 # NOTE: annotated_rhs may start with 'yield'; yield_expr must start with 'yield'
 assignment[stmt_ty]:
@@ -204,6 +205,114 @@ except_block[excepthandler_ty]:
     | 'except' ':' b=block { _Py_ExceptHandler(NULL, NULL, b, EXTRA) }
 finally_block[asdl_stmt_seq*]: 'finally' ':' a=block { a }
 
+match_stmt[stmt_ty]:
+    | "match" subject=subject_expr ':' NEWLINE INDENT cases[asdl_match_case_seq*]=case_block+ DEDENT {
+        CHECK_VERSION(stmt_ty, 10, "Pattern matching is", _Py_Match(subject, cases, EXTRA)) }
+subject_expr[expr_ty]:
+    | value=star_named_expression ',' values=star_named_expressions? {
+        _Py_Tuple(CHECK(asdl_expr_seq*, _PyPegen_seq_insert_in_front(p, value, values)), Load, EXTRA) }
+    | named_expression
+case_block[match_case_ty]:
+    | "case" pattern=patterns guard=guard? ':' body=block {
+        _Py_match_case(pattern, guard, body, p->arena) }
+guard[expr_ty]: 'if' guard=named_expression { guard }
+
+patterns[expr_ty]:
+    | values[asdl_expr_seq*]=open_sequence_pattern {
+        _Py_Tuple(values, Load, EXTRA) }
+    | pattern
+pattern[expr_ty]:
+    | as_pattern
+    | or_pattern
+as_pattern[expr_ty]:
+    | pattern=or_pattern 'as' target=capture_pattern {
+        _Py_MatchAs(pattern, target->v.Name.id, EXTRA) }
+or_pattern[expr_ty]:
+    | patterns[asdl_expr_seq*]='|'.closed_pattern+ {
+        asdl_seq_LEN(patterns) == 1 ? asdl_seq_GET(patterns, 0) : _Py_MatchOr(patterns, EXTRA) }
+closed_pattern[expr_ty]:
+    | literal_pattern
+    | capture_pattern
+    | wildcard_pattern
+    | value_pattern
+    | group_pattern
+    | sequence_pattern
+    | mapping_pattern
+    | class_pattern
+
+literal_pattern[expr_ty]:
+    | signed_number !('+' | '-')
+    | real=signed_number '+' imag=NUMBER { _Py_BinOp(real, Add, imag, EXTRA) }
+    | real=signed_number '-' imag=NUMBER  { _Py_BinOp(real, Sub, imag, EXTRA) }
+    | strings
+    | 'None' { _Py_Constant(Py_None, NULL, EXTRA) }
+    | 'True' { _Py_Constant(Py_True, NULL, EXTRA) }
+    | 'False' { _Py_Constant(Py_False, NULL, EXTRA) }
+signed_number[expr_ty]:
+    | NUMBER
+    | '-' number=NUMBER { _Py_UnaryOp(USub, number, EXTRA) }
+
+capture_pattern[expr_ty]:
+    | !"_" name=NAME !('.' | '(' | '=') {
+        _PyPegen_set_expr_context(p, name, Store) }
+
+wildcard_pattern[expr_ty]:
+    | "_" { _Py_Name(CHECK(PyObject*, _PyPegen_new_identifier(p, "_")), Store, EXTRA) }
+
+value_pattern[expr_ty]:
+    | attr=attr !('.' | '(' | '=') { attr }
+attr[expr_ty]:
+    | value=name_or_attr '.' attr=NAME {
+        _Py_Attribute(value, attr->v.Name.id, Load, EXTRA) }
+name_or_attr[expr_ty]:
+    | attr
+    | NAME
+
+group_pattern[expr_ty]:
+    | '(' pattern=pattern ')' { pattern }
+
+sequence_pattern[expr_ty]:
+    | '[' values=maybe_sequence_pattern? ']' { _Py_List(values, Load, EXTRA) }
+    | '(' values=open_sequence_pattern? ')' { _Py_Tuple(values, Load, EXTRA) }
+open_sequence_pattern[asdl_seq*]:
+    | value=maybe_star_pattern ',' values=maybe_sequence_pattern? {
+        _PyPegen_seq_insert_in_front(p, value, values) }
+maybe_sequence_pattern[asdl_seq*]:
+    | values=','.maybe_star_pattern+ ','? { values }
+maybe_star_pattern[expr_ty]:
+    | star_pattern
+    | pattern
+star_pattern[expr_ty]:
+    | '*' value=(capture_pattern | wildcard_pattern) {
+        _Py_Starred(value, Store, EXTRA) }
+
+mapping_pattern[expr_ty]:
+    | '{' items=items_pattern? '}' {
+        _Py_Dict(CHECK(asdl_expr_seq*, _PyPegen_get_keys(p, items)), CHECK(asdl_expr_seq*, _PyPegen_get_values(p, items)), EXTRA) }
+items_pattern[asdl_seq*]:
+    | items=','.key_value_pattern+ ','? { items }
+key_value_pattern[KeyValuePair*]:
+    | key=(literal_pattern | value_pattern) ':' value=pattern {
+        _PyPegen_key_value_pair(p, key, value) }
+    | double_star_pattern
+double_star_pattern[KeyValuePair*]:
+    | '**' value=capture_pattern { _PyPegen_key_value_pair(p, NULL, value) }
+
+class_pattern[expr_ty]:
+    | func=name_or_attr '(' ')' { _Py_Call(func, NULL, NULL, EXTRA) }
+    | func=name_or_attr '(' args=positional_patterns ','? ')' {
+        _Py_Call(func, args, NULL, EXTRA) }
+    | func=name_or_attr '(' keywords=keyword_patterns ','? ')' {
+        _Py_Call(func, NULL, keywords, EXTRA) }
+    | func=name_or_attr '(' args=positional_patterns ',' keywords=keyword_patterns ','? ')' {
+        _Py_Call(func, args, keywords, EXTRA) }
+positional_patterns[asdl_expr_seq*]:
+    | args[asdl_expr_seq*]=','.pattern+ { args }
+keyword_patterns[asdl_keyword_seq*]:
+    | keywords[asdl_keyword_seq*]=','.keyword_pattern+ { keywords }
+keyword_pattern[keyword_ty]:
+    | arg=NAME '=' value=pattern { _Py_keyword(arg->v.Name.id, value, EXTRA) }
+
 return_stmt[stmt_ty]:
     | 'return' a=[star_expressions] { _Py_Return(a, EXTRA) }
 
@@ -668,7 +777,7 @@ invalid_assignment:
         RAISE_SYNTAX_ERROR_INVALID_TARGET(STAR_TARGETS, a) }
     | (star_targets '=')* a=yield_expr '=' { RAISE_SYNTAX_ERROR_KNOWN_LOCATION(a, "assignment to yield expression not possible") }
     | a=star_expressions augassign (yield_expr | star_expressions) {
-        RAISE_SYNTAX_ERROR_KNOWN_LOCATION( 
+        RAISE_SYNTAX_ERROR_KNOWN_LOCATION(
             a,
             "'%s' is an illegal expression for augmented assignment",
             _PyPegen_get_expr_name(a)

Include/internal/pycore_interp.h

@@ -190,6 +190,10 @@ struct _is {
     PyObject *builtins;
     PyObject *importlib;
 
+    // Kept handy for pattern matching:
+    PyObject *map_abc;  // _collections_abc.Mapping
+    PyObject *seq_abc;  // _collections_abc.Sequence
+
     /* Used in Modules/_threadmodule.c. */
     long num_threads;
     /* Support for runtime thread stack size tuning.
@@ -290,4 +294,3 @@ PyAPI_FUNC(void) _PyInterpreterState_IDDecref(struct _is *);
 }
 #endif
 #endif /* !Py_INTERNAL_INTERP_H */
-

Include/object.h

@@ -356,6 +356,11 @@ given type object has a specified feature.
 /* Type is abstract and cannot be instantiated */
 #define Py_TPFLAGS_IS_ABSTRACT (1UL << 20)
 
+// This undocumented flag gives certain built-ins their unique pattern-matching
+// behavior, which allows a single positional subpattern to match against the
+// subject itself (rather than a mapped attribute on it):
+#define _Py_TPFLAGS_MATCH_SELF (1UL << 21)
+
 /* These flags are used to determine if a type is a subclass. */
 #define Py_TPFLAGS_LONG_SUBCLASS        (1UL << 24)
 #define Py_TPFLAGS_LIST_SUBCLASS        (1UL << 25)