On 9/6/2011 3:18 AM, Pierre Quentel wrote:
I am wondering why relative seeks fail on string IO in Python 3.2
Good question.
from io import StringIO
txt = StringIO('Favourite Worst Nightmare')
txt.seek(8) # no problem with absolute seek
Please post code without non-code indents, like so:
from io import StringIO
txt = StringIO('Favourite Worst Nightmare')
txt.seek(8,0) # no problem with absolute seek
txt.seek(0,1) # 0 characters from current position ok, and useless
txt.seek(-2,2) # end-relative gives error message for cur-relative
so someone can copy and paste without deleting indents.
I verified with 3.2.2 on Win7. I am curious what 2.7 and 3.1 do.
What system are you using? Does it have a narrow or wide unicode build?
(IE, what is the value of sys.maxunicode?)
txt.seek(2,1) # 2 characters from current position
raises "IOError: Can't do nonzero cur-relative seeks" (tested with
Python3.2.2 on WindowsXP)
A seek relative to the end of the string IO raises the same IOError
Is there any reason why relative seeks on string IO are not allowed in
Python3.2, or is it a bug that could be fixed in a next version ?
Since StringIO seeks by fixed-size code units (depending on the build),
making seeking from the current position and end trivial, I consider
this a behavior bug. At minimum, it is a doc bug. I opened
http://bugs.python.org/issue12922
As noted there, I suspect the limitation in inherited from TextIOBase.
But I challenge that it should be.
I was somewhat surprised that seeking (from the start) is not limited to
the existing text. Seeking past the end fills in with nulls. (They are
typically a nuisance though.)
from io import StringIO
txt = StringIO('0123456789')
txt.seek(15,0) # no problem with absolute seek
txt.write('xxx')
s = txt.getvalue()
print(ord(s[12]))
# 0
--
Terry Jan Reedy
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