Testing behaviours of io.BytesIO, io StringIO, cStringIO.StringIO, and StringIO.StringIO

memio.py

# coding: utf-8
from __future__ import print_function

import re
import sys

ARGUMENTS = [
    (u'()',         ()),
    (u"(b'abc')",   (b'abc',)),
    (u"(u'abc')",   (u'abc',)),
    (u"(u'αβγ')",   (u'αβγ',)),
]
CONSTRUCTORS = []

if sys.version_info >= (2, 6):
    import io
    CONSTRUCTORS += [
        (u'io.BytesIO', io.BytesIO),
        (u'io.StringIO', io.StringIO),
    ]

if sys.version_info >= (3, 0):
    def repr_(s):
        if isinstance(s, str):
            return 'u%r' % (s,)
        return repr(s)
else:
    import cStringIO
    import StringIO
    CONSTRUCTORS += [
        (u'cStringIO.StringIO', cStringIO.StringIO),
        (u'StringIO.StringIO', StringIO.StringIO),
    ]

    def repr_(s):
        if isinstance(s, bytes):
            return u'b%r' % (s,)
        if isinstance(s, unicode):
            return u"u'%s'" % (s,)
        return repr(s).decode('ascii')

PY = u'py%d.%d' % sys.version_info[:2]

print(u'{: <6}  {: <26}  {: <33}'.format(u'Python', u'Constructor', u'Result'))
print(u'{:-<6}  {:-<26}  {:-<33}'.format(u'', u'', u''))
for ctor_name, ctor in CONSTRUCTORS:
    for args_repr, args in ARGUMENTS:
        ctor_repr = u'%s%s' % (ctor_name, args_repr)
        try:
            result = ctor(*args)
        except Exception as exc:
            result = exc
            result_repr = type(exc).__name__
        else:
            result_repr = re.sub(r'at 0x[0-9a-f]+', '...', repr(result))
 
        print(u'{: <6}  {: <26}  {: <33}'.format(PY, ctor_repr, result_repr))

del result

if sys.version_info < (3, 0):
    print()
    print(u'{: <6}  {: <67}  {: <10}'.format(u'Python', u'Constructor', u'Result'))
    print(u'{:-<6}  {:-<67}  {:-<10}'.format(u'', u'', u''))
    for templ in [
        '%sStringIO.StringIO().getvalue()',
        "%sStringIO.StringIO(b'a').getvalue()",
        "%sStringIO.StringIO(u'a').getvalue()",
        r"s = StringIO.StringIO(u'\u03b1\u03b2\u03b3'); %ss.getvalue()",
        "s = StringIO.StringIO(); s.write(b'a'); %ss.getvalue()",
        "s = StringIO.StringIO(); s.write(u'a'); %ss.getvalue()",
        "s = StringIO.StringIO(); s.write(b'a'); s.write(u'a'); %ss.getvalue()",
        "s = StringIO.StringIO(); s.write(u'a'); s.write(b'a'); %ss.getvalue()",
    ]:
        label = templ % ''
        code = templ % 'result = '
        exec (code)
        print(u'{: <6}  {: <67}  {: <10}'.format(PY, label, repr_(result)))

$ python2 memio.py 
Python  Constructor                 Result                           
------  --------------------------  ---------------------------------
py2.7   io.BytesIO()                <_io.BytesIO object ...>         
py2.7   io.BytesIO(b'abc')          <_io.BytesIO object ...>         
py2.7   io.BytesIO(u'abc')          TypeError                        
py2.7   io.BytesIO(u'αβγ')          TypeError                        
py2.7   io.StringIO()               <_io.StringIO object ...>        
py2.7   io.StringIO(b'abc')         TypeError                        
py2.7   io.StringIO(u'abc')         <_io.StringIO object ...>        
py2.7   io.StringIO(u'αβγ')         <_io.StringIO object ...>        
py2.7   cStringIO.StringIO()        <cStringIO.StringO object ...>   
py2.7   cStringIO.StringIO(b'abc')  <cStringIO.StringI object ...>   
py2.7   cStringIO.StringIO(u'abc')  <cStringIO.StringI object ...>   
py2.7   cStringIO.StringIO(u'αβγ')  UnicodeEncodeError               
py2.7   StringIO.StringIO()         <StringIO.StringIO instance ...> 
py2.7   StringIO.StringIO(b'abc')   <StringIO.StringIO instance ...> 
py2.7   StringIO.StringIO(u'abc')   <StringIO.StringIO instance ...> 
py2.7   StringIO.StringIO(u'αβγ')   <StringIO.StringIO instance ...> 

Python  Constructor                                                          Result    
------  -------------------------------------------------------------------  ----------
py2.7   StringIO.StringIO().getvalue()                                       b''       
py2.7   StringIO.StringIO(b'a').getvalue()                                   b'a'      
py2.7   StringIO.StringIO(u'a').getvalue()                                   u'a'      
py2.7   s = StringIO.StringIO(u'\u03b1\u03b2\u03b3'); s.getvalue()           u'αβγ'    
py2.7   s = StringIO.StringIO(); s.write(b'a'); s.getvalue()                 b'a'      
py2.7   s = StringIO.StringIO(); s.write(u'a'); s.getvalue()                 u'a'      
py2.7   s = StringIO.StringIO(); s.write(b'a'); s.write(u'a'); s.getvalue()  u'aa'     
py2.7   s = StringIO.StringIO(); s.write(u'a'); s.write(b'a'); s.getvalue()  u'aa'     

$  python3 memio.py 
Python  Constructor                 Result                           
------  --------------------------  ---------------------------------
py3.9   io.BytesIO()                <_io.BytesIO object ...>         
py3.9   io.BytesIO(b'abc')          <_io.BytesIO object ...>         
py3.9   io.BytesIO(u'abc')          TypeError                        
py3.9   io.BytesIO(u'αβγ')          TypeError                        
py3.9   io.StringIO()               <_io.StringIO object ...>        
py3.9   io.StringIO(b'abc')         TypeError                        
py3.9   io.StringIO(u'abc')         <_io.StringIO object ...>        

For mitogen-hq/mitogen#1391

Summarised at https://github.com/mitogen-hq/mitogen/wiki/Python-2.x-3.x-compatibility-notes#in-memory-io