# -*- coding: utf-8 -*-

"""Conditionally import AST node types only supported by recent enough Python versions (3.7+)."""

__all__ = ["NamedExpr",

"Num", "Str", "Bytes", "NameConstant", "Ellipsis",

"Index", "ExtSlice",

"getconstant"]

import ast

from ..symbol import gensym

_NoSuchNodeType = gensym("_NoSuchNodeType")

# --------------------------------------------------------------------------------

# 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.

# TODO: any new AST node types in Python 3.10? (release expected in October 2021)

# --------------------------------------------------------------------------------

# 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