Python 2.x StringIO.StringIO vs io.StringIO

stringio_2x_demo.py

#1/usr/bin/env python2

import StringIO

f1 = StringIO.StringIO()
f1.write(u'unicode string')
f1.write(b'byte string')
f1.close()

import io

f2 = io.StringIO()
f2.write(u'unicode string')
f2.write(b'byte string')
f2.close()

StringIO.StringIO.write() accepts both byte strings and unicode strings, similar to Python 2.x open(). io.StringIO.write() only accepts unicode strings, similar to io.open(... 'w', encoding=...) or Python 3.x open()

$ python2 stringio_2x_demo.py
Traceback (most recent call last):
  File "stringio_2x_demo.py", line 14, in <module>
    f2.write(b'byte string')
TypeError: unicode argument expected, got 'str'