Unable to read from io.StringIO

$ python
Python 3.8.5 (default, Jul 28 2020, 12:59:40) 
[GCC 9.3.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import io
>>> buf = io.StringIO('hello world')
>>> buf.seek(0)
0
>>> import smart_open
>>> smart_open.open(buf).read()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib/python3.8/codecs.py", line 500, in read
    data = self.bytebuffer + newdata
TypeError: can't concat str to bytes

[piskvorky]

I’m not sure, would have to dig through the project history. I like @markopy 's argument, makes sense to keep smart_open’s mission clean and contained.

[markopy]

I don’t think StringIO has a peek method. Even if it did, other’s would rarely implement it. You would have to do a read followed by rewinding with seek which limits you to random access files.

In general I’m not sure accepting file objects even makes sense. Why would you call smart_open or even the built in open if you already have a file object? I can see the point of having StringIO/BytesIO work for being able to mock something in memory but beyond that I’m not convinced.

Supporting StringIO also breaks the concept of smart_open always treating the underlying file as a byte stream which complicates things and may set you up for quite a bit of maintenance pain in the future.