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Refactor run-time type checker match_value_to_typespec
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3 files changed

+125
-84
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3 files changed

+125
-84
lines changed

‎unpythonic/__init__.py‎

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@@ -39,6 +39,7 @@
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from .slicing import *
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from .symbol import *
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from .tco import *
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from .typecheck import *
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# HACK: break dependency loop
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from .lazyutil import _init_module

‎unpythonic/dispatch.py‎

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@@ -25,6 +25,7 @@
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import typing
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from .arity import resolve_bindings, _getfunc
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from .typecheck import match_value_to_typespec
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def generic(f):
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"""Decorator. Make `f` a generic function (in the sense of CLOS or Julia).
@@ -80,97 +81,14 @@ def generic(f):
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# Dispatcher - this will replace the original f.
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@wraps(f)
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def multidispatch(*args, **kwargs):
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# It's silly that while Python supports type annotations, the stdlib doesn't have a function to
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# perform a type annotation based runtime type check. Fuck it, we'll just have to implement one.
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#
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# Many `typing` meta-utilities explicitly reject using isinstance and issubclass on them,
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# so we hack those by inspecting the repr.
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#
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# value: value whose type to check
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#
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# spec: match value against this.
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# Either a concrete type, or one of the meta-utilities from the `typing` module.
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#
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# Only the most fundamental meta-utilities (Any, TypeVar, Union, Tuple, Callable)
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# are currently supported.
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#
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# TODO: This is a solved problem, we should use https://github.com/agronholm/typeguard
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def match_type(value, spec):
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# TODO: Python 3.8 adds `typing.get_origin` and `typing.get_args`, which may be useful
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# TODO: once we bump our minimum to that.
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# TODO: Right now we're accessing internal fields to get what we need.
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# https://docs.python.org/3/library/typing.html#typing.get_origin
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if spec is typing.Any:
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return True
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if repr(spec.__class__) == "TypeVar": # AnyStr gets normalized to TypeVar("AnyStr", str, bytes)
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if not spec.__constraints__: # just an abstract type name
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return True
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return any(match_type(value, typ) for typ in spec.__constraints__)
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# TODO: typing.Generic
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# if repr(spec).startswith("typing.Generic["):
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# pass
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# TODO: Protocol, Type, Iterable, Iterator, Reversible, ...
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# TODO: List, Set, FrozenSet, Dict, NamedTuple
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# TODO: many, many others; see https://docs.python.org/3/library/typing.html
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if repr(spec.__class__) == "typing.Union": # Optional gets normalized to Union[argtype, NoneType].
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if spec.__args__ is None: # bare `typing.Union`; has no types in it, so no value can match.
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return False
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if not any(match_type(value, typ) for typ in spec.__args__):
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return False
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return True
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try:
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if issubclass(spec, typing.Text):
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return isinstance(value, str)
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if issubclass(spec, typing.Tuple):
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if not isinstance(value, tuple):
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return False
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if spec.__args__ is None: # bare `typing.Tuple`, any tuple matches.
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return True
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# homogeneous type, arbitrary length
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if len(spec.__args__ == 2 and spec.__args__[1] is Ellipsis):
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typ = spec.__args__[0]
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return all(match_type(elt, typ) for elt in value)
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# heterogeneous types, exact length
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if len(value) == len(spec.__args__):
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return False
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return all(match_type(elt, typ) for typ, elt in zip(spec.__args__, value))
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if issubclass(spec, typing.Callable):
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if not callable(value):
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return False
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return True
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# # TODO: Callable[[a0, a1, ...], ret], Callable[..., ret].
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# if spec.__args__ is None: # bare `typing.Callable`, no restrictions on arg/return types.
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# return True
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# sig = typing.get_type_hints(value)
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# *argtypes, rettype = spec.__args__
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# if len(argtypes) == 1 and argtypes[0] is Ellipsis:
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# pass # argument types not specified
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# else:
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# # TODO: we need the names of the positional arguments of the `value` callable here.
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# for a in argtypes:
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# # TODO: Can't use match_type here; we're comparing two specs against each other,
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# # TODO: not a value against a spec. Need to implement a compatible_specs function.
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# if not compatible_specs(???, a):
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# return False
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# if not compatible_specs(sig["return"], rettype):
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# return False
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# return True
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except TypeError: # probably one of those meta-utilities that hates issubclass for no reason
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pass
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# TODO: typing.Literal (Python 3.8)
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# catch any meta-utilities we don't currently support
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if hasattr(spec, "__module__") and spec.__module__ == "typing":
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fullname = "{}.{}".format(spec.__module__, spec.__qualname__)
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raise NotImplementedError("This simple runtime typechecker doesn't support {}".format(fullname))
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return isinstance(value, spec) # a concrete type parameter
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# signature comes from typing.get_type_hints.
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def match_argument_types(signature):
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# TODO: handle *args (bindings["vararg"], bindings["vararg_name"])
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# TODO: handle **kwargs (bindings["kwarg"], bindings["kwarg_name"])
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for parameter, value in bindings["args"].items():
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assert parameter in signature # resolve_bindings should already TypeError when not.
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expected_type = signature[parameter]
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if not match_type(value, expected_type):
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if not match_value_to_typespec(value, expected_type):
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return False
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return True
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‎unpythonic/typecheck.py‎

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@@ -0,0 +1,122 @@
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# -*- coding: utf-8; -*-
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"""Simplistic run-time type checker.
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This implements just a minimal feature set needed for checking function arguments in
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typical uses of multiple dispatch (see `unpythonic.dispatch`).
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If you need a run-time type checker for serious general use, consider `typeguard`:
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https://github.com/agronholm/typeguard
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"""
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import typing
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__all__ = ["match_value_to_typespec"]
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# Many `typing` meta-utilities explicitly reject using isinstance and issubclass on them,
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# so we hack those by inspecting the repr.
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def match_value_to_typespec(value, T):
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"""A simple run-time type check.
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Check that `value` matches the type specification `T`.
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value: a regular run-time value whose type to check.
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T: a type specification to check against.
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Either a concrete type (e.g. `int`, `somemodule.MyClass`), or a specification
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using one of the meta-utilities defined by the `typing` module.
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Only the most fundamental meta-utilities are currently supported:
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- Any, TypeVar
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- Union, Tuple
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- Callable
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- Text
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Additionally, the `typing` module itself automatically normalizes the
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following specifications:
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- Optional[T] -> Union[T, NoneType]
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- AnyStr -> TypeVar("AnyStr", str, bytes)
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"""
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# TODO: Python 3.8 adds `typing.get_origin` and `typing.get_args`, which may be useful
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# TODO: to analyze generics once we bump our minimum Python to that.
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#
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# TODO: Right now we're accessing internal fields to get what we need.
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# https://docs.python.org/3/library/typing.html#typing.get_origin
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if T is typing.Any:
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return True
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if repr(T.__class__) == "TypeVar": # AnyStr normalizes to TypeVar("AnyStr", str, bytes)
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if not T.__constraints__: # just an abstract type name
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return True
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return any(match_value_to_typespec(value, U) for U in T.__constraints__)
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# TODO: List, Set, FrozenSet, Dict, NamedTuple
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# TODO: Protocol, Type, Iterable, Iterator, Reversible, ...
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# TODO: typing.Generic
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# if repr(T).startswith("typing.Generic["):
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# pass
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# TODO: many, many others; see https://docs.python.org/3/library/typing.html
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if repr(T.__class__) == "typing.Union": # Optional normalizes to Union[argtype, NoneType].
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if T.__args__ is None: # bare `typing.Union`; empty, has no types in it, so no value can match.
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return False
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if not any(match_value_to_typespec(value, U) for U in T.__args__):
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return False
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return True
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# many of the meta-utilities hate issubclass with a passion, so we must catch TypeError.
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try:
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if issubclass(T, typing.Text): # https://docs.python.org/3/library/typing.html#typing.Text
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return isinstance(value, str) # alias for str
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if issubclass(T, typing.Tuple):
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if not isinstance(value, tuple):
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return False
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# bare `typing.Tuple`, no restrictions on length or element type.
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if T.__args__ is None:
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return True
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# homogeneous type, arbitrary length
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if len(T.__args__) == 2 and T.__args__[1] is Ellipsis:
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U = T.__args__[0]
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return all(match_value_to_typespec(elt, U) for elt in value)
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# heterogeneous types, exact length
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if len(value) != len(T.__args__):
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return False
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return all(match_value_to_typespec(elt, U) for elt, U in zip(value, T.__args__))
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if issubclass(T, typing.Callable):
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if not callable(value):
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return False
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return True
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# # TODO: analyze Callable[[a0, a1, ...], ret], Callable[..., ret].
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# if T.__args__ is None: # bare `typing.Callable`, no restrictions on arg/return types.
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# return True
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# sig = typing.get_type_hints(value)
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# *argtypes, rettype = T.__args__
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# if len(argtypes) == 1 and argtypes[0] is Ellipsis:
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# pass # argument types not specified
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# else:
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# # TODO: we need the names of the positional arguments of the `value` callable here.
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# for a in argtypes:
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# # TODO: Can't use match_value_to_typespec here; we're comparing two specs against
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# # TODO: each other, not a value against T. Need to implement an `issubtype` function.
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# # https://en.wikipedia.org/wiki/Covariance_and_contravariance_(computer_science)
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# if not issubtype(???, a): # arg types behave contravariantly.
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# return False
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# if not issubtype(rettype, sig["return"]): # return type behaves covariantly.
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# return False
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# return True
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except TypeError as err: # probably one of those meta-utilities that hates issubclass.
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print(err)
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pass
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# TODO: typing.Literal (Python 3.8)
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# catch any meta-utilities we don't currently support
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if hasattr(T, "__module__") and T.__module__ == "typing":
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fullname = "{}.{}".format(T.__module__, T.__qualname__)
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raise NotImplementedError("This simple run-time type checker doesn't support '{}'".format(fullname))
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return isinstance(value, T) # T is a concrete class

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