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Implement RFC 58: Core support for ValueCastable formatting.

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Wanda 2024-04-03 19:32:06 +02:00 • committed by Catherine
parent f21d3d0c6a
commit 0e6d802de4
3 changed files with 133 additions and 5 deletions
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37
amaranth/hdl/_ast.py
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@ -385,6 +385,27 @@ class ShapeCastable:
"""
return super().__call__(*args, **kwargs) # :nocov:
def format(self, obj, spec):
"""Format a value.
This method is called by the Amaranth language to implement formatting for custom
shapes. Whenever :py:`"{obj:spec}"` is encountered by :class:`Format`, and :py:`obj`
has a custom shape that has a :meth:`format` method, :py:`obj.shape().format(obj, "spec")`
is called, and the format specifier is replaced with the result.
The default :meth:`format` implementation is:
.. code::
def format(self, obj, spec):
return Format(f"{{:{spec}}}", Value.cast(obj))
Returns
-------
:class:`Format`
"""
return Format(f"{{:{spec}}}", Value.cast(obj))
# TODO: write an RFC for turning this into a proper interface method
def _value_repr(self, value):
return (_repr.Repr(_repr.FormatInt(), value),)
@ -2576,14 +2597,26 @@ class Format:
chunks.append(literal)
if field_name is not None:
obj = get_field(field_name)
obj = fmt.convert_field(obj, conversion)
if conversion == "v":
obj = Value.cast(obj)
else:
obj = fmt.convert_field(obj, conversion)
format_spec = subformat(format_spec)
if isinstance(obj, Value):
# Perform validation.
self._parse_format_spec(format_spec, obj.shape())
chunks.append((obj, format_spec))
elif isinstance(obj, ValueCastable):
raise TypeError("'ValueCastable' formatting is not supported")
shape = obj.shape()
if isinstance(shape, ShapeCastable):
fmt = shape.format(obj, format_spec)
if not isinstance(fmt, Format):
raise TypeError(f"`ShapeCastable.format` must return a 'Format' instance, not {fmt!r}")
chunks += fmt._chunks
else:
obj = Value.cast(obj)
self._parse_format_spec(format_spec, obj.shape())
chunks.append((obj, format_spec))
elif isinstance(obj, Format):
if format_spec != "":
raise ValueError(f"Format specifiers ({format_spec!r}) cannot be used for 'Format' objects")