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from types import ModuleType
import weakref
from numba.core.errors import ConstantInferenceError, NumbaError
from numba.core import ir
class ConstantInference(object):
"""
A constant inference engine for a given interpreter.
Inference inspects the IR to try and compute a compile-time constant for
a variable.
This shouldn't be used directly, instead call Interpreter.infer_constant().
"""
def __init__(self, func_ir):
# Avoid cyclic references as some user-visible objects may be
# held alive in the cache
self._func_ir = weakref.proxy(func_ir)
self._cache = {}
def infer_constant(self, name, loc=None):
"""
Infer a constant value for the given variable *name*.
If no value can be inferred, numba.errors.ConstantInferenceError
is raised.
"""
if name not in self._cache:
try:
self._cache[name] = (True, self._do_infer(name))
except ConstantInferenceError as exc:
# Store the exception args only, to avoid keeping
# a whole traceback alive.
self._cache[name] = (False, (exc.__class__, exc.args))
success, val = self._cache[name]
if success:
return val
else:
exc, args = val
if issubclass(exc, NumbaError):
raise exc(*args, loc=loc)
else:
raise exc(*args)
def _fail(self, val):
# The location here is set to None because `val` is the ir.Var name
# and not the actual offending use of the var. When this is raised it is
# caught in the flow control of `infer_constant` and the class and args
# (the message) are captured and then raised again but with the location
# set to the expression that caused the constant inference error.
raise ConstantInferenceError(
"Constant inference not possible for: %s" % (val,), loc=None)
def _do_infer(self, name):
if not isinstance(name, str):
raise TypeError("infer_constant() called with non-str %r"
% (name,))
try:
defn = self._func_ir.get_definition(name)
except KeyError:
raise ConstantInferenceError(
"no single definition for %r" % (name,))
try:
const = defn.infer_constant()
except ConstantInferenceError:
if isinstance(defn, ir.Expr):
return self._infer_expr(defn)
self._fail(defn)
return const
def _infer_expr(self, expr):
# Infer an expression: handle supported cases
if expr.op == 'call':
func = self.infer_constant(expr.func.name, loc=expr.loc)
return self._infer_call(func, expr)
elif expr.op == 'getattr':
value = self.infer_constant(expr.value.name, loc=expr.loc)
return self._infer_getattr(value, expr)
elif expr.op == 'build_list':
return [self.infer_constant(i.name, loc=expr.loc) for i in
expr.items]
elif expr.op == 'build_tuple':
return tuple(self.infer_constant(i.name, loc=expr.loc) for i in
expr.items)
self._fail(expr)
def _infer_call(self, func, expr):
if expr.kws or expr.vararg:
self._fail(expr)
# Check supported callables
_slice = func in (slice,)
_exc = isinstance(func, type) and issubclass(func, BaseException)
if _slice or _exc:
args = [self.infer_constant(a.name, loc=expr.loc) for a in
expr.args]
if _slice:
return func(*args)
elif _exc:
# If the exception class is user defined it may implement a ctor
# that does not pass the args to the super. Therefore return the
# raw class and the args so this can be instantiated at the call
# site in the way the user source expects it to be.
return func, args
else:
assert 0, 'Unreachable'
self._fail(expr)
def _infer_getattr(self, value, expr):
if isinstance(value, (ModuleType, type)):
# Allow looking up a constant on a class or module
try:
return getattr(value, expr.attr)
except AttributeError:
pass
self._fail(expr)