Confusing about StringIO, cStringIO and ByteIO

You should use io.StringIO for handling unicode objects and io.BytesIO for handling bytes objects in both python 2 and 3, for forwards-compatibility (this is all 3 has to offer).

Here's a better test (for python 2 and 3), that doesn't include conversion costs from numpy to str/bytes

import numpy as npimport stringb_data = np.random.choice(list(string.printable), size=1000000).tobytes()u_data = b_data.decode('ascii')u_data = u'\u2603' + u_data[1:]  # add a non-ascii character

And then:

import io%timeit io.StringIO(u_data)%timeit io.StringIO(b_data)%timeit io.BytesIO(u_data)%timeit io.BytesIO(b_data)

In python 2, you can also test:

import StringIO, cStringIO%timeit cStringIO.StringIO(u_data)%timeit cStringIO.StringIO(b_data)%timeit StringIO.StringIO(u_data)%timeit StringIO.StringIO(b_data)

Some of these will crash, complaining about non-ascii characters

Python 3.5 results:

>>> %timeit io.StringIO(u_data)100 loops, best of 3: 8.61 ms per loop>>> %timeit io.StringIO(b_data)TypeError: initial_value must be str or None, not bytes>>> %timeit io.BytesIO(u_data)TypeError: a bytes-like object is required, not 'str'>>> %timeit io.BytesIO(b_data)The slowest run took 6.79 times longer than the fastest. This could mean that an intermediate result is being cached1000000 loops, best of 3: 344 ns per loop

Python 2.7 results (run on a different machine):

>>> %timeit io.StringIO(u_data)1000 loops, best of 3: 304 µs per loop>>> %timeit io.StringIO(b_data)TypeError: initial_value must be unicode or None, not str>>> %timeit io.BytesIO(u_data)TypeError: 'unicode' does not have the buffer interface>>> %timeit io.BytesIO(b_data)10000 loops, best of 3: 77.5 µs per loop

>>> %timeit cStringIO.StringIO(u_data)UnicodeEncodeError: 'ascii' codec cant encode character u'\u2603' in position 0: ordinal not in range(128)>>> %timeit cStringIO.StringIO(b_data)1000000 loops, best of 3: 448 ns per loop>>> %timeit StringIO.StringIO(u_data)1000000 loops, best of 3: 1.15 µs per loop>>> %timeit StringIO.StringIO(b_data)1000000 loops, best of 3: 1.19 µs per loop