Experiment with python3 nested file streams to test if closing the tip stream will actually close the internal and the root streams.

nested_streams_close_experiment.py

""" 
Experiment with python3 nested file streams to test if closing the tip stream will actually close
the internal and the root streams.
"""

import io
import gzip

FILE_PATH = "experiments/data/nested_stream_close_experiment.txt.gz"


print("# EXPERIMENT: Check if the tip stream closes the internal and the root streams.")

# pylint: disable=locally-disabled, consider-using-with
root_stream = open(FILE_PATH, "rb")
internal_stream = gzip.GzipFile(fileobj = root_stream, mode = "r")
tip_stream = io.TextIOWrapper(internal_stream)
for _ in tip_stream:
    pass
tip_stream.close()


if internal_stream.closed:
    print("# RESULT: Internal stream closed")
else:
    print("# RESULT: Internal stream not closed")
    internal_stream.close()

if root_stream.closed:
    print("# RESULT: Root stream closed")
else:
    print("# RESULT: Root stream not closed")
    root_stream.close()


### Output ###
# EXPERIMENT: Check if the tip stream closes the internal and the root streams.
# RESULT: Internal stream closed
# RESULT: Root stream not closed

### Conclusion ###
# After some research, passing in a fileobj to a GzipFile is documented to not close the internal
# stream since the internal stream could be used for other purpose later in the code. Thus when
# an intermediary GzipFile is involved, the referenced fileobj should be explicitly closed or
# inside a "with" statement.
#
# See https://docs.python.org/3/library/gzip.html for details.