StringIO and compatibility with 'with' statement (context manager)

Question

I have some legacy code with a legacy function that takes a filename as an argument and processes the file contents. A working facsimile of the code is below.

What

Answer 1

A StringIO instance is an open file already. The open command, on the other hand, only takes filenames, to return an open file. A StringIO instance is not suitable as a filename.

Also, you don't need to close a StringIO instance, so there is no need to use it as a context manager either.

If all your legacy code can take is a filename, then a StringIO instance is not the way to go. Use the tempfile module to generate a temporary filename instead.

Here is an example using a contextmanager to ensure the temp file is cleaned up afterwards:

import os
import tempfile
from contextlib import contextmanager

@contextmanager
def tempinput(data):
    temp = tempfile.NamedTemporaryFile(delete=False)
    temp.write(data)
    temp.close()
    try:
        yield temp.name
    finally:
        os.unlink(temp.name)

with tempinput('Some data.\nSome more data.') as tempfilename:
    processFile(tempfilename)

You can also switch to the newer Python 3 infrastructure offered by the io module (available in Python 2 and 3), where io.BytesIO is the more robust replacement for StringIO.StringIO / cStringIO.StringIO. This object does support being used as a context manager (but still can't be passed to open()).