353 lines
14 KiB
Python
353 lines
14 KiB
Python
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# 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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"""Module to enforce different constraints on flags.
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Flags validators can be registered using following functions / decorators::
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flags.register_validator
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@flags.validator
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flags.register_multi_flags_validator
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@flags.multi_flags_validator
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Three convenience functions are also provided for common flag constraints::
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flags.mark_flag_as_required
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flags.mark_flags_as_required
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flags.mark_flags_as_mutual_exclusive
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flags.mark_bool_flags_as_mutual_exclusive
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See their docstring in this module for a usage manual.
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Do NOT import this module directly. Import the flags package and use the
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aliases defined at the package level instead.
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"""
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import warnings
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from absl.flags import _exceptions
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from absl.flags import _flagvalues
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from absl.flags import _validators_classes
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def register_validator(flag_name,
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checker,
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message='Flag validation failed',
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flag_values=_flagvalues.FLAGS):
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"""Adds a constraint, which will be enforced during program execution.
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The constraint is validated when flags are initially parsed, and after each
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change of the corresponding flag's value.
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Args:
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flag_name: str | FlagHolder, name or holder of the flag to be checked.
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Positional-only parameter.
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checker: callable, a function to validate the flag.
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* input - A single positional argument: The value of the corresponding
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flag (string, boolean, etc. This value will be passed to checker
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by the library).
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* output - bool, True if validator constraint is satisfied.
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If constraint is not satisfied, it should either ``return False`` or
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``raise flags.ValidationError(desired_error_message)``.
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message: str, error text to be shown to the user if checker returns False.
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If checker raises flags.ValidationError, message from the raised
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error will be shown.
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flag_values: flags.FlagValues, optional FlagValues instance to validate
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against.
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Raises:
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AttributeError: Raised when flag_name is not registered as a valid flag
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name.
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ValueError: Raised when flag_values is non-default and does not match the
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FlagValues of the provided FlagHolder instance.
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"""
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flag_name, flag_values = _flagvalues.resolve_flag_ref(flag_name, flag_values)
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v = _validators_classes.SingleFlagValidator(flag_name, checker, message)
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_add_validator(flag_values, v)
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def validator(flag_name, message='Flag validation failed',
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flag_values=_flagvalues.FLAGS):
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"""A function decorator for defining a flag validator.
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Registers the decorated function as a validator for flag_name, e.g.::
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@flags.validator('foo')
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def _CheckFoo(foo):
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...
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See :func:`register_validator` for the specification of checker function.
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Args:
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flag_name: str | FlagHolder, name or holder of the flag to be checked.
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Positional-only parameter.
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message: str, error text to be shown to the user if checker returns False.
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If checker raises flags.ValidationError, message from the raised
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error will be shown.
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flag_values: flags.FlagValues, optional FlagValues instance to validate
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against.
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Returns:
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A function decorator that registers its function argument as a validator.
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Raises:
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AttributeError: Raised when flag_name is not registered as a valid flag
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name.
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"""
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def decorate(function):
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register_validator(flag_name, function,
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message=message,
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flag_values=flag_values)
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return function
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return decorate
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def register_multi_flags_validator(flag_names,
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multi_flags_checker,
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message='Flags validation failed',
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flag_values=_flagvalues.FLAGS):
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"""Adds a constraint to multiple flags.
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The constraint is validated when flags are initially parsed, and after each
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change of the corresponding flag's value.
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Args:
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flag_names: [str | FlagHolder], a list of the flag names or holders to be
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checked. Positional-only parameter.
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multi_flags_checker: callable, a function to validate the flag.
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* input - dict, with keys() being flag_names, and value for each key
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being the value of the corresponding flag (string, boolean, etc).
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* output - bool, True if validator constraint is satisfied.
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If constraint is not satisfied, it should either return False or
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raise flags.ValidationError.
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message: str, error text to be shown to the user if checker returns False.
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If checker raises flags.ValidationError, message from the raised
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error will be shown.
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flag_values: flags.FlagValues, optional FlagValues instance to validate
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against.
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Raises:
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AttributeError: Raised when a flag is not registered as a valid flag name.
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ValueError: Raised when multiple FlagValues are used in the same
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invocation. This can occur when FlagHolders have different `_flagvalues`
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or when str-type flag_names entries are present and the `flag_values`
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argument does not match that of provided FlagHolder(s).
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"""
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flag_names, flag_values = _flagvalues.resolve_flag_refs(
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flag_names, flag_values)
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v = _validators_classes.MultiFlagsValidator(
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flag_names, multi_flags_checker, message)
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_add_validator(flag_values, v)
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def multi_flags_validator(flag_names,
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message='Flag validation failed',
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flag_values=_flagvalues.FLAGS):
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"""A function decorator for defining a multi-flag validator.
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Registers the decorated function as a validator for flag_names, e.g.::
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@flags.multi_flags_validator(['foo', 'bar'])
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def _CheckFooBar(flags_dict):
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...
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See :func:`register_multi_flags_validator` for the specification of checker
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function.
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Args:
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flag_names: [str | FlagHolder], a list of the flag names or holders to be
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checked. Positional-only parameter.
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message: str, error text to be shown to the user if checker returns False.
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If checker raises flags.ValidationError, message from the raised
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error will be shown.
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flag_values: flags.FlagValues, optional FlagValues instance to validate
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against.
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Returns:
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A function decorator that registers its function argument as a validator.
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Raises:
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AttributeError: Raised when a flag is not registered as a valid flag name.
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"""
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def decorate(function):
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register_multi_flags_validator(flag_names,
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function,
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message=message,
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flag_values=flag_values)
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return function
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return decorate
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def mark_flag_as_required(flag_name, flag_values=_flagvalues.FLAGS):
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"""Ensures that flag is not None during program execution.
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Registers a flag validator, which will follow usual validator rules.
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Important note: validator will pass for any non-``None`` value, such as
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``False``, ``0`` (zero), ``''`` (empty string) and so on.
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If your module might be imported by others, and you only wish to make the flag
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required when the module is directly executed, call this method like this::
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if __name__ == '__main__':
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flags.mark_flag_as_required('your_flag_name')
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app.run()
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Args:
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flag_name: str | FlagHolder, name or holder of the flag.
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Positional-only parameter.
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flag_values: flags.FlagValues, optional :class:`~absl.flags.FlagValues`
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instance where the flag is defined.
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Raises:
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AttributeError: Raised when flag_name is not registered as a valid flag
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name.
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ValueError: Raised when flag_values is non-default and does not match the
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FlagValues of the provided FlagHolder instance.
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"""
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flag_name, flag_values = _flagvalues.resolve_flag_ref(flag_name, flag_values)
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if flag_values[flag_name].default is not None:
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warnings.warn(
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'Flag --%s has a non-None default value; therefore, '
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'mark_flag_as_required will pass even if flag is not specified in the '
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'command line!' % flag_name,
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stacklevel=2)
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register_validator(
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flag_name,
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lambda value: value is not None,
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message='Flag --{} must have a value other than None.'.format(flag_name),
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flag_values=flag_values)
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def mark_flags_as_required(flag_names, flag_values=_flagvalues.FLAGS):
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"""Ensures that flags are not None during program execution.
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If your module might be imported by others, and you only wish to make the flag
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required when the module is directly executed, call this method like this::
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if __name__ == '__main__':
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flags.mark_flags_as_required(['flag1', 'flag2', 'flag3'])
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app.run()
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Args:
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flag_names: Sequence[str | FlagHolder], names or holders of the flags.
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flag_values: flags.FlagValues, optional FlagValues instance where the flags
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are defined.
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Raises:
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AttributeError: If any of flag name has not already been defined as a flag.
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"""
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for flag_name in flag_names:
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mark_flag_as_required(flag_name, flag_values)
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def mark_flags_as_mutual_exclusive(flag_names, required=False,
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flag_values=_flagvalues.FLAGS):
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"""Ensures that only one flag among flag_names is not None.
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Important note: This validator checks if flag values are ``None``, and it does
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not distinguish between default and explicit values. Therefore, this validator
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does not make sense when applied to flags with default values other than None,
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including other false values (e.g. ``False``, ``0``, ``''``, ``[]``). That
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includes multi flags with a default value of ``[]`` instead of None.
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Args:
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flag_names: [str | FlagHolder], names or holders of flags.
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Positional-only parameter.
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required: bool. If true, exactly one of the flags must have a value other
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than None. Otherwise, at most one of the flags can have a value other
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than None, and it is valid for all of the flags to be None.
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flag_values: flags.FlagValues, optional FlagValues instance where the flags
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are defined.
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Raises:
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ValueError: Raised when multiple FlagValues are used in the same
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invocation. This can occur when FlagHolders have different `_flagvalues`
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or when str-type flag_names entries are present and the `flag_values`
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argument does not match that of provided FlagHolder(s).
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"""
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flag_names, flag_values = _flagvalues.resolve_flag_refs(
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flag_names, flag_values)
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for flag_name in flag_names:
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if flag_values[flag_name].default is not None:
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warnings.warn(
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'Flag --{} has a non-None default value. That does not make sense '
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'with mark_flags_as_mutual_exclusive, which checks whether the '
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'listed flags have a value other than None.'.format(flag_name),
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stacklevel=2)
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def validate_mutual_exclusion(flags_dict):
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flag_count = sum(1 for val in flags_dict.values() if val is not None)
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if flag_count == 1 or (not required and flag_count == 0):
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return True
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raise _exceptions.ValidationError(
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'{} one of ({}) must have a value other than None.'.format(
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'Exactly' if required else 'At most', ', '.join(flag_names)))
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register_multi_flags_validator(
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flag_names, validate_mutual_exclusion, flag_values=flag_values)
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def mark_bool_flags_as_mutual_exclusive(flag_names, required=False,
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flag_values=_flagvalues.FLAGS):
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"""Ensures that only one flag among flag_names is True.
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Args:
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flag_names: [str | FlagHolder], names or holders of flags.
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Positional-only parameter.
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required: bool. If true, exactly one flag must be True. Otherwise, at most
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one flag can be True, and it is valid for all flags to be False.
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flag_values: flags.FlagValues, optional FlagValues instance where the flags
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are defined.
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Raises:
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ValueError: Raised when multiple FlagValues are used in the same
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invocation. This can occur when FlagHolders have different `_flagvalues`
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or when str-type flag_names entries are present and the `flag_values`
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argument does not match that of provided FlagHolder(s).
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"""
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flag_names, flag_values = _flagvalues.resolve_flag_refs(
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flag_names, flag_values)
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for flag_name in flag_names:
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if not flag_values[flag_name].boolean:
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raise _exceptions.ValidationError(
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'Flag --{} is not Boolean, which is required for flags used in '
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'mark_bool_flags_as_mutual_exclusive.'.format(flag_name))
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def validate_boolean_mutual_exclusion(flags_dict):
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flag_count = sum(bool(val) for val in flags_dict.values())
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if flag_count == 1 or (not required and flag_count == 0):
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return True
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raise _exceptions.ValidationError(
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'{} one of ({}) must be True.'.format(
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'Exactly' if required else 'At most', ', '.join(flag_names)))
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register_multi_flags_validator(
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flag_names, validate_boolean_mutual_exclusion, flag_values=flag_values)
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def _add_validator(fv, validator_instance):
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"""Register new flags validator to be checked.
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Args:
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fv: flags.FlagValues, the FlagValues instance to add the validator.
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validator_instance: validators.Validator, the validator to add.
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Raises:
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KeyError: Raised when validators work with a non-existing flag.
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"""
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for flag_name in validator_instance.get_flags_names():
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fv[flag_name].validators.append(validator_instance)
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