105 lines
3.1 KiB
Python
105 lines
3.1 KiB
Python
|
# Copyright 2019 The TensorFlow Authors. All Rights Reserved.
|
||
|
|
#
|
||
|
|
# Licensed under the Apache License, Version 2.0 (the "License");
|
||
|
|
# you may not use this file except in compliance with the License.
|
||
|
|
# You may obtain a copy of the License at
|
||
|
|
#
|
||
|
|
# http://www.apache.org/licenses/LICENSE-2.0
|
||
|
|
#
|
||
|
|
# Unless required by applicable law or agreed to in writing, software
|
||
|
|
# distributed under the License is distributed on an "AS IS" BASIS,
|
||
|
|
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
|
||
|
|
# See the License for the specific language governing permissions and
|
||
|
|
# limitations under the License.
|
||
|
|
# ==============================================================================
|
||
|
|
"""Utilities used to capture Python idioms."""
|
||
|
|
|
||
|
|
|
||
|
|
def ld(v):
|
||
|
|
"""Load variable operator."""
|
||
|
|
if isinstance(v, Undefined):
|
||
|
|
return v.read()
|
||
|
|
return v
|
||
|
|
|
||
|
|
|
||
|
|
def ldu(load_v, name):
|
||
|
|
"""Load variable operator that returns Undefined when failing to evaluate.
|
||
|
|
|
||
|
|
Note: the name ("load or return undefined") is abbreviated to minimize
|
||
|
|
the amount of clutter in generated code.
|
||
|
|
|
||
|
|
This variant of `ld` is useful when loading symbols that may be undefined at
|
||
|
|
runtime, such as composite symbols, and whether they are defined or not cannot
|
||
|
|
be determined statically. For example `d['a']` is undefined when `d` is an
|
||
|
|
empty dict.
|
||
|
|
|
||
|
|
Args:
|
||
|
|
load_v: Lambda that executes the actual read.
|
||
|
|
name: Human-readable name of the symbol being read.
|
||
|
|
Returns:
|
||
|
|
Either the value of the symbol, or Undefined, if the symbol is not fully
|
||
|
|
defined.
|
||
|
|
"""
|
||
|
|
try:
|
||
|
|
# TODO(mdan): Use locals()/globals() here.
|
||
|
|
return load_v()
|
||
|
|
except (KeyError, AttributeError, NameError):
|
||
|
|
return Undefined(name)
|
||
|
|
|
||
|
|
|
||
|
|
class Undefined(object):
|
||
|
|
"""Represents an undefined symbol in Python.
|
||
|
|
|
||
|
|
This is used to reify undefined symbols, which is required to use the
|
||
|
|
functional form of loops.
|
||
|
|
Example:
|
||
|
|
|
||
|
|
while n > 0:
|
||
|
|
n = n - 1
|
||
|
|
s = n
|
||
|
|
return s # Runtime error if n == 0
|
||
|
|
|
||
|
|
This is valid Python code and will not result in an error as long as n
|
||
|
|
is positive. The use of this class is to stay as close to Python semantics
|
||
|
|
as possible for staged code of this nature.
|
||
|
|
|
||
|
|
Converted version of the above showing the possible usage of this class:
|
||
|
|
|
||
|
|
s = Undefined('s')
|
||
|
|
init_state = (s,)
|
||
|
|
s = while_loop(cond, body, init_state)
|
||
|
|
return s # s is an instance of Undefined if the loop never runs
|
||
|
|
|
||
|
|
Attributes:
|
||
|
|
symbol_name: Text, identifier for the undefined symbol
|
||
|
|
"""
|
||
|
|
|
||
|
|
__slots__ = ('symbol_name',)
|
||
|
|
|
||
|
|
def __init__(self, symbol_name):
|
||
|
|
self.symbol_name = symbol_name
|
||
|
|
|
||
|
|
def read(self):
|
||
|
|
raise UnboundLocalError("'{}' is used before assignment".format(
|
||
|
|
self.symbol_name))
|
||
|
|
|
||
|
|
def __repr__(self):
|
||
|
|
return self.symbol_name
|
||
|
|
|
||
|
|
def __getattribute__(self, name):
|
||
|
|
try:
|
||
|
|
# If it's an existing attribute, return it.
|
||
|
|
return object.__getattribute__(self, name)
|
||
|
|
except AttributeError:
|
||
|
|
# Otherwise return Undefined.
|
||
|
|
return self
|
||
|
|
|
||
|
|
def __getitem__(self, i):
|
||
|
|
return self
|
||
|
|
|
||
|
|
|
||
|
|
# TODO(mdan): Refactor as a RetVal object, aggregating the value and do_return.
|
||
|
|
class UndefinedReturnValue(object):
|
||
|
|
"""Represents a return value that is undefined."""
|
||
|
|
pass
|