Python Gflags

3.1.2 · deprecated · verified Wed Apr 15

Python-gflags is a Python implementation of the Google command-line flags module, enabling distributed command-line systems by allowing flags to be defined across different modules. It is currently at version 3.1.2. This library is now obsolete and no longer maintained; users are strongly encouraged to migrate to `absl-py` for continued support and new features.

Warnings

breaking The entire `python-gflags` library is deprecated and no longer actively maintained. All new development has moved to `absl-py`, specifically `absl.flags`. Users should plan to migrate to `absl-py` to receive updates and avoid unmaintained dependencies.
Fix: Migrate your codebase to use `absl-py`. The `python-gflags` 3.1.2 release included API name changes to ease compatibility. Refer to the `absl-py` migration guidelines.
breaking Version 3.1.0 introduced significant breaking changes, including: removal of `UnrecognizedFlag` (now `UnparsedFlagAccessError` can be raised for premature flag access), replacement of `DuplicateFlag` with `DuplicateFlagError`, renaming of `IllegalFlagValue` to `IllegalFlagValueError`, and moving `validators.Error` to `exceptions.ValidationError`. Several methods like `MutualExclusionValidator`, `FlagValues.AddValidator`, and `_helpers.GetMainModule` were removed.
Fix: Update exception handling and API calls according to the new naming conventions and removed functionality. Consult the GitHub release notes for 3.1.0 and absl migration guide.
gotcha If `python-gflags` and `absl.flags` are both present in the same process, it can lead to two global `FLAGS` objects coexisting, causing unexpected behavior and conflicts during flag definition and parsing.
Fix: Ensure that your project and its dependencies are consistently using either `python-gflags` or `absl-py`, but not both. Prioritize migrating to `absl-py`.
gotcha Accessing flag values before command-line arguments have been parsed by calling `FLAGS(sys.argv)` can raise an `UnparsedFlagAccessError` in newer versions. Additionally, `FLAGS.set_default` no longer overrides the current value if the flag has already been set via command line or direct assignment.
Fix: Always ensure `FLAGS(sys.argv)` is called early in your application's lifecycle before attempting to access any flag values. Be aware of the new `FLAGS.set_default` behavior.

Install

pip install python-gflags Install latest version

Imports

FLAGS
wrong:
```
from gflags import FLAGS
```
correct:
```
import gflags as flags
FLAGS = flags.FLAGS
```
While `from gflags import FLAGS` works, the idiomatic and safer way is to import `gflags` as `flags` and then assign `FLAGS = flags.FLAGS` to avoid potential naming conflicts and clearly denote where FLAGS originates.

DEFINE_string

import gflags as flags
flags.DEFINE_string('name', 'default', 'help string')

DEFINE_integer

import gflags as flags
flags.DEFINE_integer('count', 0, 'help string')

Quickstart

Defines two flags (`name` and `age`) and a boolean `debug` flag. It then parses command-line arguments and prints a greeting. Run with `python your_script.py --name=Python --age=10 --debug`.

import sys
import gflags as flags

FLAGS = flags.FLAGS

flags.DEFINE_string('name', 'World', 'Your name.')
flags.DEFINE_integer('age', 30, 'Your age in years.', lower_bound=0)
flags.DEFINE_boolean('debug', False, 'Enable debug output.')

def main(argv):
    try:
        argv = FLAGS(argv)
    except flags.FlagsError as e:
        print(f'{e}\nUsage: {sys.argv[0]} ARGS\n{FLAGS}')
        sys.exit(1)

    if FLAGS.debug:
        print(f'Debug mode enabled. Non-flag arguments: {argv}')

    print(f'Hello, {FLAGS.name}! You are {FLAGS.age} years old.')

if __name__ == '__main__':
    main(sys.argv)

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