StringIO / cStringIO inconsistency with unicode

[arigo]

BPO	1678411
Nosy	@loewis, @arigo

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = <Date 2007-03-12.00:04:16.000>
created_at = <Date 2007-03-11.18:07:00.000>
labels = ['invalid', 'library']
title = 'StringIO / cStringIO inconsistency with unicode'
updated_at = <Date 2007-03-12.00:04:16.000>
user = 'https://github.com/arigo'

bugs.python.org fields:

activity = <Date 2007-03-12.00:04:16.000>
actor = 'arigo'
assignee = 'none'
closed = True
closed_date = None
closer = None
components = ['Library (Lib)']
creation = <Date 2007-03-11.18:07:00.000>
creator = 'arigo'
dependencies = []
files = []
hgrepos = []
issue_num = 1678411
keywords = []
message_count = 3.0
messages = ['31490', '31491', '31492']
nosy_count = 2.0
nosy_names = ['loewis', 'arigo']
pr_nums = []
priority = 'normal'
resolution = 'not a bug'
stage = None
status = 'closed'
superseder = None
type = None
url = 'https://bugs.python.org/issue1678411'
versions = []

[arigo]

When trying to write unicode strings into a
StringIO.StringIO() or a cStringIO.StringIO()
file, different things occur. (This causes
a failing test in the "mako" project if
cStringIO is not available.) Compare the
following with StringIO or with cStringIO:

    f = StringIO()
    f.write("\xC0")
    f.write(u"hello")
    print f.getvalue()

With cStringIO, unicode strings are
immediately encoded as ascii and the
getvalue() returns '\xC0hello'. With
StringIO, on the other hand, the
getvalue() crashes in a ''.join()
trying to convert 'xC0' to unicode.
Normal file() objects follow the same
behavior as cStringIO, so my guess is
that StringIO.py is wrong here.

[loewis]

It's intentional that they behave differently. StringIO supports Unicode strings, cStringIO doesn't. This means that you can build up a large Unicode string with StringIO, but not with cStringIO.

What should happen when you mix them is debatable.

[arigo]

I missed the documentation, which already desribes
this difference.