why does smart_open.s3.Reader doesn't implement __enter__ and __exit__ method

Problem description

Hi, I am trying to add alicloud oss support. While I am reading source code of smart_open.s3.Reader, I found smart_open.s3.Reader doesn’t implement __enter__ and __exit__ method.

How is it possible to write code like:

with open('s3://commoncrawl/robots.txt', 'rb') as fin:
    for line in fin:
        print(repr(line.decode('utf-8')))
        break

[mpenkov]

The reader/writer in smart_open.s3 does not need to implement the context manager protocol, because it gets wrapped by other classes that implement that protocol.

The example code you posted actually works. Have a look at the readme - it’s the main use case.

[njn007]

@mpenkov , thanks for your explanation, I checked the python io docs, finding that S3.Reader -> io.BufferedIOBase -> io.IOBase. While IOBase is also a context manager and therefore supports the with statement which means that you don’t need to implement __enter__ method if you just want to return the reader itself. the __enter__ method is implemented in base class io.IOBase def __enter__(): return self

The reader/writer in smart_open.s3 does not need to implement the context manager protocol, because it gets wrapped by other classes that implement that protocol.