move unpythonic.syntax.astcompat to mcpyrate.astcompat

mcpyrate/astcompat.py

@@ -0,0 +1,86 @@
+# -*- coding: utf-8 -*-
+"""Conditionally import AST node types only supported by recent enough Python versions."""
+
+__all__ = ["NamedExpr",
+           "Match", "match_case", "MatchValue", "MatchSingleton", "MatchSequence", "MatchStar", "MatchMapping", "MatchClass", "MatchAs", "MatchOr",
+           "TryStar",
+           "TypeAlias", "TypeVar", "ParamSpec", "TypeVarTuple",
+           "Num", "Str", "Bytes", "NameConstant", "Ellipsis",
+           "Index", "ExtSlice",
+           "getconstant"]
+
+import ast
+
+class _NoSuchNodeType(ast.AST):
+    pass
+
+# --------------------------------------------------------------------------------
+# New AST node types
+
+# Minimum language version supported by this module is Python 3.6.
+
+# No new AST node types in Python 3.7.
+
+try:  # Python 3.8+
+    from ast import NamedExpr  # a.k.a. walrus operator ":="
+except ImportError:  # pragma: no cover
+    NamedExpr = _NoSuchNodeType
+
+# No new AST node types in Python 3.9.
+
+try:  # Python 3.10+
+    from ast import (Match, match_case,
+                     MatchValue, MatchSingleton, MatchSequence, MatchStar,
+                     MatchMapping, MatchClass, MatchAs, MatchOr)  # `match`/`case`
+except ImportError:  # pragma: no cover
+    Match = match_case = MatchValue = MatchSingleton = MatchSequence = MatchStar = MatchMapping = MatchClass = MatchAs = MatchOr = _NoSuchNodeType
+
+try:  # Python 3.11+
+    from ast import TryStar  # `try`/`except*` (exception groups)
+except ImportError:  # pragma: no cover
+    TryStar = _NoSuchNodeType
+
+try:  # Python 3.12+
+    from ast import TypeAlias, TypeVar, ParamSpec, TypeVarTuple  # `type` statement (type alias)
+except ImportError:  # pragma: no cover
+    TypeAlias = TypeVar = ParamSpec = TypeVarTuple = _NoSuchNodeType
+
+# --------------------------------------------------------------------------------
+# Deprecated AST node types
+
+try:  # Python 3.8+, https://docs.python.org/3/whatsnew/3.8.html#deprecated
+    from ast import Num, Str, Bytes, NameConstant, Ellipsis
+except ImportError:  # pragma: no cover
+    Num = Str = Bytes = NameConstant = Ellipsis = _NoSuchNodeType
+
+try:  # Python 3.9+, https://docs.python.org/3/whatsnew/3.9.html#deprecated
+    from ast import Index, ExtSlice
+    # We ignore the internal classes Suite, Param, AugLoad, AugStore,
+    # which were never used in Python 3.x.
+except ImportError:  # pragma: no cover
+    Index = ExtSlice = _NoSuchNodeType
+
+# --------------------------------------------------------------------------------
+# Compatibility functions
+
+def getconstant(tree):
+    """Given an AST node `tree` representing a constant, return the contained raw value.
+
+    This encapsulates the AST differences between Python 3.8+ and older versions.
+
+    There are no `setconstant` or `makeconstant` counterparts, because you can
+    just create an `ast.Constant` in Python 3.6 and later. The parser doesn't
+    emit them until Python 3.8, but Python 3.6+ compile `ast.Constant` just fine.
+    """
+    if type(tree) is ast.Constant:  # Python 3.8+
+        return tree.value
+    # up to Python 3.7
+    elif type(tree) is ast.NameConstant:  # up to Python 3.7  # pragma: no cover
+        return tree.value
+    elif type(tree) is ast.Num:  # pragma: no cover
+        return tree.n
+    elif type(tree) in (ast.Str, ast.Bytes):  # pragma: no cover
+        return tree.s
+    elif type(tree) is ast.Ellipsis:  # `ast.Ellipsis` is the AST node type, `builtins.Ellipsis` is `...`.  # pragma: no cover
+        return ...
+    raise TypeError(f"Not an AST node representing a constant: {type(tree)} with value {repr(tree)}")  # pragma: no cover