nchint opened a new pull request, #30563:
URL: https://github.com/apache/beam/pull/30563
## Background
Suppose you have the following script
```python
import argparse
from apache_beam.options.pipeline_options import PipelineOptions
PipelineOptions()
assert False
```
Here's is the behavior when running this script
```bash
$ python3 test.py
Traceback (most recent call last):
File "/Users/chintala/./test.py", line 5, in <module>
assert False
AssertionError
$ python3 test.py -h
usage: test.py [-h]
options:
-h, --help show this help message and exit
```
During `__init__` of `PipelineOptions` we make a call to `parse_known_args`
with the `self._flags` field. The behavior of `parse_known_args` is if it is
given `None` as an argument it will use `sys.argv` for the argument list and
parse those. If `-h` is within the argument list `parse_known_args` will print
the help statement and then exit the python process.
The ultimately means that if you run a python script that defines a
`PipelineOptions` at top level and supply `-h` in the command line arguments
your program will exist upon instantiating `PipelineOptions` which is undesired
behavior.
## Solution
Instead of defaults `self._flags` to `None` we set it to an empty list
instead. This means when we call `parse_known_args` it will never read from
`sys.argv`.
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