[ python-Bugs-1476356 ] StringIO should implement __str__()

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Bugs item #1476356, was opened at 2006-04-25 16:11
Message generated for change (Comment added) made by cinamod
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Category: Python Library
Group: None
Status: Closed
Resolution: Invalid
Priority: 5
Submitted By: Dom Lachowicz (cinamod)
Assigned to: Nobody/Anonymous (nobody)
Summary: StringIO should implement __str__()

Initial Comment:
I was a bit surprised when I discovered that StringIO
didn't have a __str__() method, equivalent to
getvalue(). Calling str(stringio_object) gives the
following:

>>> import StringIO
>>> s = StringIO.StringIO("hello world")
>>> print "%s" % (str(s))
<StringIO.StringIO instance at 0x401ef08c>

I had some (perhaps dodgy code) code that did:

if isinstance(data, types.FileType):
  return data.read()
else:
  return str(data)

Since StringIO doesn't subclass any file type and
doesn't implement a __str__() method, I was getting
seemingly bogus results. This was trivially worked
around by adding another "isinstance(data,
StringIO.StringIO)" case, but it was surprising
nonetheless. Thanks.

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>Comment By: Dom Lachowicz (cinamod)
Date: 2006-04-26 11:09

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Since section 2.3.9 of the docs doesn't mention anything
about an overriden meaning of FILE.__str__(), its meaning in
that API is undefined. "Correctly emulating" undefined API
is impossible.

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Comment By: Dom Lachowicz (cinamod)
Date: 2006-04-25 22:54

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The StringIO API diverges from the file API already. It adds
API (getvalue()) doesn't implement the encoding, mode, name,
newlines, or softspace attributes, and implements isatty()
in violation of the section 2.3.9 docs.

In some contexts, it may look like a file, but it isn't a
file. And I don't see how implementing __str__() changes
that. It's equivalent to saying that Java's StringBuffer
class shouldn't override toString()...

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Comment By: Dom Lachowicz (cinamod)
Date: 2006-04-25 22:53

Message:
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user_id=69417

The StringIO API diverges from the file API already. It adds
API (getvalue()) doesn't implement the encoding, mode, name,
newlines, or softspace attributes, and implements isatty()
in violation of the section 2.3.9 docs.

In some contexts, it may look like a file, but it isn't a
file. And I don't see how implementing __str__() changes
that. It's equivalent to saying that Java's StringBuffer
class shouldn't override toString()...

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Comment By: Raymond Hettinger (rhettinger)
Date: 2006-04-25 18:58

Message:
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user_id=80475

This isn't a bug.  The module is correctly emulating the API
for file objects.

I recommend replacing your isintance() test with a try/except:

try:
.... return data.read()
except AttributeError:
.... return str(data)



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