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# imports
from collections import abc
import typing
# bsfs imports
from bsfs.utils import URI, typename, normalize_args
# exports
__all__ : typing.Sequence[str] = (
'All',
'Fetch',
'FetchExpression',
'Node',
'This',
'Value',
)
## code ##
class FetchExpression(abc.Hashable):
"""Generic Fetch expression."""
def __repr__(self) -> str:
"""Return the expressions's string representation."""
return f'{typename(self)}()'
def __hash__(self) -> int:
"""Return the expression's integer representation."""
return hash(type(self))
def __eq__(self, other: typing.Any) -> bool:
"""Return True if *self* and *other* are equivalent."""
return isinstance(other, type(self))
class All(FetchExpression):
"""Fetch all child expressions."""
# child expressions.
expr: typing.Set[FetchExpression]
def __init__(self, *expr):
# unpack child expressions
unfolded = set(normalize_args(*expr))
# check child expressions
if len(unfolded) == 0:
raise AttributeError('expected at least one expression, found none')
if not all(isinstance(itm, FetchExpression) for itm in unfolded):
raise TypeError(expr)
# initialize
super().__init__()
# assign members
self.expr = unfolded
def __iter__(self) -> typing.Iterator[FetchExpression]:
return iter(self.expr)
def __len__(self) -> int:
return len(self.expr)
def __repr__(self) -> str:
return f'{typename(self)}({self.expr})'
def __hash__(self) -> int:
return hash((super().__hash__(), tuple(sorted(self.expr, key=repr))))
def __eq__(self, other: typing.Any) -> bool:
return super().__eq__(other) and self.expr == other.expr
class _Branch(FetchExpression):
"""Branch along a predicate."""
# FIXME: Use a Predicate (like in ast.filter) so that we can also reverse them!
# predicate to follow.
predicate: URI
def __init__(self, predicate: URI):
if not isinstance(predicate, URI):
raise TypeError(predicate)
self.predicate = predicate
def __repr__(self) -> str:
return f'{typename(self)}({self.predicate})'
def __hash__(self) -> int:
return hash((super().__hash__(), self.predicate))
def __eq__(self, other: typing.Any) -> bool:
return super().__eq__(other) and self.predicate == other.predicate
class Fetch(_Branch):
"""Follow a predicate before evaluating a child epxression."""
# child expression.
expr: FetchExpression
def __init__(self, predicate: URI, expr: FetchExpression):
# check child expressions
if not isinstance(expr, FetchExpression):
raise TypeError(expr)
# initialize
super().__init__(predicate)
# assign members
self.expr = expr
def __repr__(self) -> str:
return f'{typename(self)}({self.predicate}, {self.expr})'
def __hash__(self) -> int:
return hash((super().__hash__(), self.expr))
def __eq__(self, other: typing.Any) -> bool:
return super().__eq__(other) and self.expr == other.expr
class _Named(_Branch):
"""Fetch a (named) symbol at a predicate."""
# symbol name.
name: str
def __init__(self, predicate: URI, name: str):
super().__init__(predicate)
self.name = str(name)
def __repr__(self) -> str:
return f'{typename(self)}({self.predicate}, {self.name})'
def __hash__(self) -> int:
return hash((super().__hash__(), self.name))
def __eq__(self, other: typing.Any) -> bool:
return super().__eq__(other) and self.name == other.name
class Node(_Named): # pylint: disable=too-few-public-methods
"""Fetch a Node at a predicate."""
# FIXME: Is this actually needed?
class Value(_Named): # pylint: disable=too-few-public-methods
"""Fetch a Literal at a predicate."""
class This(FetchExpression):
"""Fetch the current Node."""
# symbol name.
name: str
def __init__(self, name: str):
super().__init__()
self.name = str(name)
def __repr__(self) -> str:
return f'{typename(self)}({self.name})'
def __hash__(self) -> int:
return hash((super().__hash__(), self.name))
def __eq__(self, other: typing.Any) -> bool:
return super().__eq__(other) and self.name == other.name
## EOF ##
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