394 lines
13 KiB
Python
394 lines
13 KiB
Python
# Copyright 2017 The Abseil Authors.
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#
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# Licensed under the Apache License, Version 2.0 (the "License");
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# you may not use this file except in compliance with the License.
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# You may obtain a copy of the License at
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#
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# http://www.apache.org/licenses/LICENSE-2.0
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#
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# Unless required by applicable law or agreed to in writing, software
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# distributed under the License is distributed on an "AS IS" BASIS,
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# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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# See the License for the specific language governing permissions and
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# limitations under the License.
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"""Decorator and context manager for saving and restoring flag values.
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There are many ways to save and restore. Always use the most convenient method
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for a given use case.
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Here are examples of each method. They all call ``do_stuff()`` while
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``FLAGS.someflag`` is temporarily set to ``'foo'``::
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from absl.testing import flagsaver
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# Use a decorator which can optionally override flags via arguments.
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@flagsaver.flagsaver(someflag='foo')
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def some_func():
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do_stuff()
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# Use a decorator which can optionally override flags with flagholders.
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@flagsaver.flagsaver((module.FOO_FLAG, 'foo'), (other_mod.BAR_FLAG, 23))
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def some_func():
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do_stuff()
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# Use a decorator which does not override flags itself.
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@flagsaver.flagsaver
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def some_func():
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FLAGS.someflag = 'foo'
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do_stuff()
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# Use a context manager which can optionally override flags via arguments.
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with flagsaver.flagsaver(someflag='foo'):
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do_stuff()
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# Save and restore the flag values yourself.
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saved_flag_values = flagsaver.save_flag_values()
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try:
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FLAGS.someflag = 'foo'
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do_stuff()
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finally:
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flagsaver.restore_flag_values(saved_flag_values)
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# Use the parsing version to emulate users providing the flags.
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# Note that all flags must be provided as strings (unparsed).
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@flagsaver.as_parsed(some_int_flag='123')
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def some_func():
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# Because the flag was parsed it is considered "present".
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assert FLAGS.some_int_flag.present
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do_stuff()
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# flagsaver.as_parsed() can also be used as a context manager just like
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# flagsaver.flagsaver()
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with flagsaver.as_parsed(some_int_flag='123'):
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do_stuff()
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# The flagsaver.as_parsed() interface also supports FlagHolder objects.
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@flagsaver.as_parsed((module.FOO_FLAG, 'foo'), (other_mod.BAR_FLAG, '23'))
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def some_func():
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do_stuff()
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# Using as_parsed with a multi_X flag requires a sequence of strings.
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@flagsaver.as_parsed(some_multi_int_flag=['123', '456'])
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def some_func():
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assert FLAGS.some_multi_int_flag.present
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do_stuff()
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# If a flag name includes non-identifier characters it can be specified like
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# so:
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@flagsaver.as_parsed(**{'i-like-dashes': 'true'})
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def some_func():
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do_stuff()
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We save and restore a shallow copy of each Flag object's ``__dict__`` attribute.
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This preserves all attributes of the flag, such as whether or not it was
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overridden from its default value.
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WARNING: Currently a flag that is saved and then deleted cannot be restored. An
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exception will be raised. However if you *add* a flag after saving flag values,
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and then restore flag values, the added flag will be deleted with no errors.
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"""
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import collections
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import functools
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import inspect
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from typing import Any, Callable, Dict, Mapping, Sequence, Tuple, Type, TypeVar, Union, overload
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from absl import flags
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FLAGS = flags.FLAGS
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# The type of pre/post wrapped functions.
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_CallableT = TypeVar('_CallableT', bound=Callable)
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@overload
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def flagsaver(func: _CallableT) -> _CallableT:
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...
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@overload
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def flagsaver(
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*args: Tuple[flags.FlagHolder, Any], **kwargs: Any
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) -> '_FlagOverrider':
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...
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def flagsaver(*args, **kwargs):
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"""The main flagsaver interface. See module doc for usage."""
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return _construct_overrider(_FlagOverrider, *args, **kwargs) # type: ignore[bad-return-type]
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@overload
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def as_parsed(*args: Tuple[flags.FlagHolder, Union[str, Sequence[str]]],
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**kwargs: Union[str, Sequence[str]]) -> '_ParsingFlagOverrider':
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...
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@overload
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def as_parsed(func: _CallableT) -> _CallableT:
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...
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def as_parsed(*args, **kwargs):
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"""Overrides flags by parsing strings, saves flag state similar to flagsaver.
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This function can be used as either a decorator or context manager similar to
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flagsaver.flagsaver(). However, where flagsaver.flagsaver() directly sets the
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flags to new values, this function will parse the provided arguments as if
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they were provided on the command line. Among other things, this will cause
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`FLAGS['flag_name'].present == True`.
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A note on unparsed input: For many flag types, the unparsed version will be
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a single string. However for multi_x (multi_string, multi_integer, multi_enum)
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the unparsed version will be a Sequence of strings.
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Args:
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*args: Tuples of FlagHolders and their unparsed value.
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**kwargs: The keyword args are flag names, and the values are unparsed
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values.
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Returns:
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_ParsingFlagOverrider that serves as a context manager or decorator. Will
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save previous flag state and parse new flags, then on cleanup it will
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restore the previous flag state.
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"""
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return _construct_overrider(_ParsingFlagOverrider, *args, **kwargs)
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# NOTE: the order of these overload declarations matters. The type checker will
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# pick the first match which could be incorrect.
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@overload
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def _construct_overrider(
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flag_overrider_cls: Type['_ParsingFlagOverrider'],
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*args: Tuple[flags.FlagHolder, Union[str, Sequence[str]]],
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**kwargs: Union[str, Sequence[str]]) -> '_ParsingFlagOverrider':
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...
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@overload
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def _construct_overrider(
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flag_overrider_cls: Type['_FlagOverrider'], func: _CallableT
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) -> _CallableT:
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...
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@overload
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def _construct_overrider(
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flag_overrider_cls: Type['_FlagOverrider'],
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*args: Tuple[flags.FlagHolder, Any],
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**kwargs: Any,
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) -> '_FlagOverrider':
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...
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def _construct_overrider(flag_overrider_cls, *args, **kwargs):
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"""Handles the args/kwargs returning an instance of flag_overrider_cls.
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If flag_overrider_cls is _FlagOverrider then values should be native python
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types matching the python types. Otherwise if flag_overrider_cls is
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_ParsingFlagOverrider the values should be strings or sequences of strings.
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Args:
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flag_overrider_cls: The class that will do the overriding.
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*args: Tuples of FlagHolder and the new flag value.
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**kwargs: Keword args mapping flag name to new flag value.
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Returns:
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A _FlagOverrider to be used as a decorator or context manager.
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"""
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if not args:
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return flag_overrider_cls(**kwargs)
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# args can be [func] if used as `@flagsaver` instead of `@flagsaver(...)`
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if len(args) == 1 and callable(args[0]):
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if kwargs:
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raise ValueError(
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"It's invalid to specify both positional and keyword parameters.")
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func = args[0]
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if inspect.isclass(func):
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raise TypeError('@flagsaver.flagsaver cannot be applied to a class.')
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return _wrap(flag_overrider_cls, func, {})
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# args can be a list of (FlagHolder, value) pairs.
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# In which case they augment any specified kwargs.
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for arg in args:
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if not isinstance(arg, tuple) or len(arg) != 2:
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raise ValueError('Expected (FlagHolder, value) pair, found %r' % (arg,))
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holder, value = arg
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if not isinstance(holder, flags.FlagHolder):
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raise ValueError('Expected (FlagHolder, value) pair, found %r' % (arg,))
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if holder.name in kwargs:
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raise ValueError('Cannot set --%s multiple times' % holder.name)
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kwargs[holder.name] = value
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return flag_overrider_cls(**kwargs)
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def save_flag_values(
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flag_values: flags.FlagValues = FLAGS,
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) -> Dict[str, Dict[str, Any]]:
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"""Returns copy of flag values as a dict.
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Args:
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flag_values: FlagValues, the FlagValues instance with which the flag will be
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saved. This should almost never need to be overridden.
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Returns:
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Dictionary mapping keys to values. Keys are flag names, values are
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corresponding ``__dict__`` members. E.g. ``{'key': value_dict, ...}``.
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"""
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return {name: _copy_flag_dict(flag_values[name]) for name in flag_values}
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def restore_flag_values(
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saved_flag_values: Mapping[str, Dict[str, Any]],
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flag_values: flags.FlagValues = FLAGS,
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) -> None:
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"""Restores flag values based on the dictionary of flag values.
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Args:
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saved_flag_values: {'flag_name': value_dict, ...}
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flag_values: FlagValues, the FlagValues instance from which the flag will be
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restored. This should almost never need to be overridden.
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"""
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new_flag_names = list(flag_values)
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for name in new_flag_names:
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saved = saved_flag_values.get(name)
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if saved is None:
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# If __dict__ was not saved delete "new" flag.
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delattr(flag_values, name)
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else:
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if flag_values[name].value != saved['_value']:
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flag_values[name].value = saved['_value'] # Ensure C++ value is set.
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flag_values[name].__dict__ = saved
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@overload
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def _wrap(flag_overrider_cls: Type['_FlagOverrider'], func: _CallableT,
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overrides: Mapping[str, Any]) -> _CallableT:
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...
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@overload
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def _wrap(flag_overrider_cls: Type['_ParsingFlagOverrider'], func: _CallableT,
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overrides: Mapping[str, Union[str, Sequence[str]]]) -> _CallableT:
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...
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def _wrap(flag_overrider_cls, func, overrides):
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"""Creates a wrapper function that saves/restores flag values.
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Args:
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flag_overrider_cls: The class that will be used as a context manager.
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func: This will be called between saving flags and restoring flags.
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overrides: Flag names mapped to their values. These flags will be set after
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saving the original flag state. The type of the values depends on if
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_FlagOverrider or _ParsingFlagOverrider was specified.
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Returns:
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A wrapped version of func.
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"""
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@functools.wraps(func)
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def _flagsaver_wrapper(*args, **kwargs):
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"""Wrapper function that saves and restores flags."""
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with flag_overrider_cls(**overrides):
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return func(*args, **kwargs)
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return _flagsaver_wrapper
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class _FlagOverrider:
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"""Overrides flags for the duration of the decorated function call.
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It also restores all original values of flags after decorated method
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completes.
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"""
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def __init__(self, **overrides: Any):
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self._overrides = overrides
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self._saved_flag_values = None
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def __call__(self, func: _CallableT) -> _CallableT:
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if inspect.isclass(func):
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raise TypeError('flagsaver cannot be applied to a class.')
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return _wrap(self.__class__, func, self._overrides)
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def __enter__(self):
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self._saved_flag_values = save_flag_values(FLAGS)
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try:
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FLAGS._set_attributes(**self._overrides)
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except:
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# It may fail because of flag validators.
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restore_flag_values(self._saved_flag_values, FLAGS)
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raise
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def __exit__(self, exc_type, exc_value, traceback):
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restore_flag_values(self._saved_flag_values, FLAGS)
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class _ParsingFlagOverrider(_FlagOverrider):
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"""Context manager for overriding flags.
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Simulates command line parsing.
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This is simlar to _FlagOverrider except that all **overrides should be
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strings or sequences of strings, and when context is entered this class calls
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.parse(value)
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This results in the flags having .present set properly.
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"""
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def __init__(self, **overrides: Union[str, Sequence[str]]):
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for flag_name, new_value in overrides.items():
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if isinstance(new_value, str):
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continue
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if (isinstance(new_value, collections.abc.Sequence) and
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all(isinstance(single_value, str) for single_value in new_value)):
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continue
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raise TypeError(
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f'flagsaver.as_parsed() cannot parse {flag_name}. Expected a single '
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f'string or sequence of strings but {type(new_value)} was provided.')
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super().__init__(**overrides)
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def __enter__(self):
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self._saved_flag_values = save_flag_values(FLAGS)
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try:
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for flag_name, unparsed_value in self._overrides.items():
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# LINT.IfChange(flag_override_parsing)
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FLAGS[flag_name].parse(unparsed_value)
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FLAGS[flag_name].using_default_value = False
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# LINT.ThenChange()
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# Perform the validation on all modified flags. This is something that
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# FLAGS._set_attributes() does for you in _FlagOverrider.
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for flag_name in self._overrides:
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FLAGS._assert_validators(FLAGS[flag_name].validators)
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except KeyError as e:
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# If a flag doesn't exist, an UnrecognizedFlagError is more specific.
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restore_flag_values(self._saved_flag_values, FLAGS)
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raise flags.UnrecognizedFlagError('Unknown command line flag.') from e
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except:
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# It may fail because of flag validators or general parsing issues.
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restore_flag_values(self._saved_flag_values, FLAGS)
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raise
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def _copy_flag_dict(flag: flags.Flag) -> Dict[str, Any]:
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"""Returns a copy of the flag object's ``__dict__``.
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It's mostly a shallow copy of the ``__dict__``, except it also does a shallow
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copy of the validator list.
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Args:
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flag: flags.Flag, the flag to copy.
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Returns:
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A copy of the flag object's ``__dict__``.
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"""
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copy = flag.__dict__.copy()
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copy['_value'] = flag.value # Ensure correct restore for C++ flags.
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copy['validators'] = list(flag.validators)
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return copy
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