Wrap an open stream with io.TextIOWrapper

Question

How can I wrap an open binary stream – a Python 2 file, a Python 3 io.BufferedReader, an io.BytesIO – in an io.TextIOWrapper

Answer 1

Here's some code that I've tested in both python 2.7 and python 3.6.

The key here is that you need to use detach() on your previous stream first. This does not close the underlying file, it just rips out the raw stream object so that it can be reused. detach() will return an object that is wrappable with TextIOWrapper.

As an example here, I open a file in binary read mode, do a read on it like that, then I switch to a UTF-8 decoded text stream via io.TextIOWrapper.

I saved this example as this-file.py

import io

fileName = 'this-file.py'
fp = io.open(fileName,'rb')
fp.seek(20)
someBytes = fp.read(10)
print(type(someBytes) + len(someBytes))

# now let's do some wrapping to get a new text (non-binary) stream
pos = fp.tell() # we're about to lose our position, so let's save it
newStream = io.TextIOWrapper(fp.detach(),'utf-8') # FYI -- fp is now unusable
newStream.seek(pos)
theRest = newStream.read()
print(type(theRest), len(theRest))

Here's what I get when I run it with both python2 and python3.

$ python2.7 this-file.py 
(, 10)
(, 406)
$ python3.6 this-file.py 
 10
 406

Obviously the print syntax is different and as expected the variable types differ between python versions but works like it should in both cases.