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460 lines
14 KiB
460 lines
14 KiB
# 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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"""Generic entry point for Abseil Python applications.
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To use this module, define a 'main' function with a single 'argv' argument and
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call app.run(main). For example:
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def main(argv):
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if len(argv) > 1:
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raise app.UsageError('Too many command-line arguments.')
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if __name__ == '__main__':
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app.run(main)
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"""
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from __future__ import absolute_import
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from __future__ import division
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from __future__ import print_function
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import collections
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import errno
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import os
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import pdb
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import sys
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import traceback
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from absl import command_name
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from absl import flags
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from absl import logging
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try:
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import faulthandler
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except ImportError:
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faulthandler = None
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FLAGS = flags.FLAGS
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flags.DEFINE_boolean('run_with_pdb', False, 'Set to true for PDB debug mode')
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flags.DEFINE_boolean('pdb_post_mortem', False,
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'Set to true to handle uncaught exceptions with PDB '
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'post mortem.')
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flags.DEFINE_boolean('run_with_profiling', False,
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'Set to true for profiling the script. '
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'Execution will be slower, and the output format might '
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'change over time.')
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flags.DEFINE_string('profile_file', None,
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'Dump profile information to a file (for python -m '
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'pstats). Implies --run_with_profiling.')
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flags.DEFINE_boolean('use_cprofile_for_profiling', True,
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'Use cProfile instead of the profile module for '
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'profiling. This has no effect unless '
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'--run_with_profiling is set.')
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flags.DEFINE_boolean('only_check_args', False,
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'Set to true to validate args and exit.',
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allow_hide_cpp=True)
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# If main() exits via an abnormal exception, call into these
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# handlers before exiting.
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EXCEPTION_HANDLERS = []
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class Error(Exception):
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pass
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class UsageError(Error):
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"""Exception raised when the arguments supplied by the user are invalid.
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Raise this when the arguments supplied are invalid from the point of
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view of the application. For example when two mutually exclusive
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flags have been supplied or when there are not enough non-flag
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arguments. It is distinct from flags.Error which covers the lower
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level of parsing and validating individual flags.
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"""
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def __init__(self, message, exitcode=1):
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super(UsageError, self).__init__(message)
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self.exitcode = exitcode
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class HelpFlag(flags.BooleanFlag):
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"""Special boolean flag that displays usage and raises SystemExit."""
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NAME = 'help'
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SHORT_NAME = '?'
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def __init__(self):
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super(HelpFlag, self).__init__(
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self.NAME, False, 'show this help',
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short_name=self.SHORT_NAME, allow_hide_cpp=True)
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def parse(self, arg):
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if arg:
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usage(shorthelp=True, writeto_stdout=True)
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# Advertise --helpfull on stdout, since usage() was on stdout.
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print()
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print('Try --helpfull to get a list of all flags.')
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sys.exit(1)
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class HelpshortFlag(HelpFlag):
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"""--helpshort is an alias for --help."""
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NAME = 'helpshort'
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SHORT_NAME = None
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class HelpfullFlag(flags.BooleanFlag):
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"""Display help for flags in the main module and all dependent modules."""
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def __init__(self):
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super(HelpfullFlag, self).__init__(
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'helpfull', False, 'show full help', allow_hide_cpp=True)
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def parse(self, arg):
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if arg:
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usage(writeto_stdout=True)
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sys.exit(1)
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class HelpXMLFlag(flags.BooleanFlag):
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"""Similar to HelpfullFlag, but generates output in XML format."""
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def __init__(self):
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super(HelpXMLFlag, self).__init__(
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'helpxml', False, 'like --helpfull, but generates XML output',
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allow_hide_cpp=True)
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def parse(self, arg):
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if arg:
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flags.FLAGS.write_help_in_xml_format(sys.stdout)
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sys.exit(1)
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def parse_flags_with_usage(args):
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"""Tries to parse the flags, print usage, and exit if unparseable.
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Args:
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args: [str], a non-empty list of the command line arguments including
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program name.
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Returns:
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[str], a non-empty list of remaining command line arguments after parsing
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flags, including program name.
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"""
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try:
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return FLAGS(args)
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except flags.Error as error:
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sys.stderr.write('FATAL Flags parsing error: %s\n' % error)
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sys.stderr.write('Pass --helpshort or --helpfull to see help on flags.\n')
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sys.exit(1)
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_define_help_flags_called = False
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def define_help_flags():
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"""Registers help flags. Idempotent."""
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# Use a global to ensure idempotence.
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global _define_help_flags_called
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if not _define_help_flags_called:
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flags.DEFINE_flag(HelpFlag())
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flags.DEFINE_flag(HelpshortFlag()) # alias for --help
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flags.DEFINE_flag(HelpfullFlag())
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flags.DEFINE_flag(HelpXMLFlag())
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_define_help_flags_called = True
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def _register_and_parse_flags_with_usage(
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argv=None,
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flags_parser=parse_flags_with_usage,
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):
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"""Registers help flags, parses arguments and shows usage if appropriate.
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This also calls sys.exit(0) if flag --only_check_args is True.
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Args:
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argv: [str], a non-empty list of the command line arguments including
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program name, sys.argv is used if None.
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flags_parser: Callable[[List[Text]], Any], the function used to parse flags.
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The return value of this function is passed to `main` untouched.
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It must guarantee FLAGS is parsed after this function is called.
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Returns:
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The return value of `flags_parser`. When using the default `flags_parser`,
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it returns the following:
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[str], a non-empty list of remaining command line arguments after parsing
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flags, including program name.
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Raises:
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Error: Raised when flags_parser is called, but FLAGS is not parsed.
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SystemError: Raised when it's called more than once.
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"""
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if _register_and_parse_flags_with_usage.done:
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raise SystemError('Flag registration can be done only once.')
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define_help_flags()
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original_argv = sys.argv if argv is None else argv
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args_to_main = flags_parser(original_argv)
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if not FLAGS.is_parsed():
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raise Error('FLAGS must be parsed after flags_parser is called.')
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# Exit when told so.
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if FLAGS.only_check_args:
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sys.exit(0)
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# Immediately after flags are parsed, bump verbosity to INFO if the flag has
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# not been set.
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if FLAGS['verbosity'].using_default_value:
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FLAGS.verbosity = 0
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_register_and_parse_flags_with_usage.done = True
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return args_to_main
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_register_and_parse_flags_with_usage.done = False
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def _run_main(main, argv):
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"""Calls main, optionally with pdb or profiler."""
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if FLAGS.run_with_pdb:
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sys.exit(pdb.runcall(main, argv))
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elif FLAGS.run_with_profiling or FLAGS.profile_file:
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# Avoid import overhead since most apps (including performance-sensitive
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# ones) won't be run with profiling.
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import atexit
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if FLAGS.use_cprofile_for_profiling:
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import cProfile as profile
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else:
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import profile
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profiler = profile.Profile()
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if FLAGS.profile_file:
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atexit.register(profiler.dump_stats, FLAGS.profile_file)
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else:
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atexit.register(profiler.print_stats)
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retval = profiler.runcall(main, argv)
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sys.exit(retval)
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else:
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sys.exit(main(argv))
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def _call_exception_handlers(exception):
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"""Calls any installed exception handlers."""
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for handler in EXCEPTION_HANDLERS:
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try:
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if handler.wants(exception):
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handler.handle(exception)
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except: # pylint: disable=bare-except
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try:
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# We don't want to stop for exceptions in the exception handlers but
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# we shouldn't hide them either.
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logging.error(traceback.format_exc())
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except: # pylint: disable=bare-except
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# In case even the logging statement fails, ignore.
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pass
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def run(
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main,
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argv=None,
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flags_parser=parse_flags_with_usage,
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):
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"""Begins executing the program.
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Args:
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main: The main function to execute. It takes an single argument "argv",
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which is a list of command line arguments with parsed flags removed.
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If it returns an integer, it is used as the process's exit code.
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argv: A non-empty list of the command line arguments including program name,
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sys.argv is used if None.
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flags_parser: Callable[[List[Text]], Any], the function used to parse flags.
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The return value of this function is passed to `main` untouched.
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It must guarantee FLAGS is parsed after this function is called.
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- Parses command line flags with the flag module.
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- If there are any errors, prints usage().
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- Calls main() with the remaining arguments.
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- If main() raises a UsageError, prints usage and the error message.
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"""
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try:
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args = _run_init(
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sys.argv if argv is None else argv,
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flags_parser,
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)
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while _init_callbacks:
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callback = _init_callbacks.popleft()
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callback()
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try:
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_run_main(main, args)
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except UsageError as error:
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usage(shorthelp=True, detailed_error=error, exitcode=error.exitcode)
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except:
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if FLAGS.pdb_post_mortem:
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traceback.print_exc()
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pdb.post_mortem()
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raise
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except Exception as e:
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_call_exception_handlers(e)
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raise
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# Callbacks which have been deferred until after _run_init has been called.
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_init_callbacks = collections.deque()
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def call_after_init(callback):
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"""Calls the given callback only once ABSL has finished initialization.
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If ABSL has already finished initialization when `call_after_init` is
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called then the callback is executed immediately, otherwise `callback` is
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stored to be executed after `app.run` has finished initializing (aka. just
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before the main function is called).
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If called after `app.run`, this is equivalent to calling `callback()` in the
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caller thread. If called before `app.run`, callbacks are run sequentially (in
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an undefined order) in the same thread as `app.run`.
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Args:
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callback: a callable to be called once ABSL has finished initialization.
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This may be immediate if initialization has already finished. It
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takes no arguments and returns nothing.
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"""
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if _run_init.done:
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callback()
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else:
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_init_callbacks.append(callback)
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def _run_init(
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argv,
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flags_parser,
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):
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"""Does one-time initialization and re-parses flags on rerun."""
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if _run_init.done:
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return flags_parser(argv)
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command_name.make_process_name_useful()
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# Set up absl logging handler.
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logging.use_absl_handler()
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args = _register_and_parse_flags_with_usage(
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argv=argv,
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flags_parser=flags_parser,
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)
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if faulthandler:
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try:
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faulthandler.enable()
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except Exception: # pylint: disable=broad-except
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# Some tests verify stderr output very closely, so don't print anything.
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# Disabled faulthandler is a low-impact error.
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pass
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_run_init.done = True
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return args
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_run_init.done = False
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def usage(shorthelp=False, writeto_stdout=False, detailed_error=None,
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exitcode=None):
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"""Writes __main__'s docstring to stderr with some help text.
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Args:
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shorthelp: bool, if True, prints only flags from the main module,
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rather than all flags.
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writeto_stdout: bool, if True, writes help message to stdout,
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rather than to stderr.
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detailed_error: str, additional detail about why usage info was presented.
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exitcode: optional integer, if set, exits with this status code after
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writing help.
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"""
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if writeto_stdout:
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stdfile = sys.stdout
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else:
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stdfile = sys.stderr
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doc = sys.modules['__main__'].__doc__
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if not doc:
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doc = '\nUSAGE: %s [flags]\n' % sys.argv[0]
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doc = flags.text_wrap(doc, indent=' ', firstline_indent='')
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else:
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# Replace all '%s' with sys.argv[0], and all '%%' with '%'.
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num_specifiers = doc.count('%') - 2 * doc.count('%%')
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try:
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doc %= (sys.argv[0],) * num_specifiers
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except (OverflowError, TypeError, ValueError):
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# Just display the docstring as-is.
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pass
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if shorthelp:
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flag_str = FLAGS.main_module_help()
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else:
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flag_str = FLAGS.get_help()
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try:
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stdfile.write(doc)
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if flag_str:
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stdfile.write('\nflags:\n')
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stdfile.write(flag_str)
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stdfile.write('\n')
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if detailed_error is not None:
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stdfile.write('\n%s\n' % detailed_error)
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except IOError as e:
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# We avoid printing a huge backtrace if we get EPIPE, because
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# "foo.par --help | less" is a frequent use case.
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if e.errno != errno.EPIPE:
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raise
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if exitcode is not None:
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sys.exit(exitcode)
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class ExceptionHandler(object):
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"""Base exception handler from which other may inherit."""
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def wants(self, exc):
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"""Returns whether this handler wants to handle the exception or not.
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This base class returns True for all exceptions by default. Override in
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subclass if it wants to be more selective.
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Args:
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exc: Exception, the current exception.
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"""
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del exc # Unused.
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return True
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def handle(self, exc):
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"""Do something with the current exception.
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Args:
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exc: Exception, the current exception
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This method must be overridden.
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"""
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raise NotImplementedError()
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def install_exception_handler(handler):
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"""Installs an exception handler.
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Args:
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handler: ExceptionHandler, the exception handler to install.
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Raises:
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TypeError: Raised when the handler was not of the correct type.
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All installed exception handlers will be called if main() exits via
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an abnormal exception, i.e. not one of SystemExit, KeyboardInterrupt,
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FlagsError or UsageError.
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"""
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if not isinstance(handler, ExceptionHandler):
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raise TypeError('handler of type %s does not inherit from ExceptionHandler'
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% type(handler))
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EXCEPTION_HANDLERS.append(handler)
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