Bugs item #1569057, was opened at 2006-10-01 23:49
Message generated for change (Comment added) made by montanaro
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Category: Documentation
Group: Python 2.5
Status: Open
Resolution: None
Priority: 5
Submitted By: andrei kulakov (rainy)
Assigned to: Nobody/Anonymous (nobody)
Summary: Using .next() on file open in write mode writes junk to file
Initial Comment:
When you open a file in write mode and use .next(), it
prints an error and writes many lines of junk to file.
I tested on windows and python 2.5:
>>> f = open('test', 'w')
>>> f.fileno()
4
>>> f.write('1\n')
>>> f.write('2\n3\n4\n')
>>> f.next()
Traceback (most recent call last):
File "<pyshell#8>", line 1, in <module>
f.next()
IOError: [Errno 9] Bad file descriptor
>>> f.close()
>>> f = open('test')
>>> f.next()
'1\n'
>>> f.next()
'2\n'
>>> f.next()
'3\n'
>>> f.next()
'4\n'
>>> f.next()
'\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x
00\x00\x00\x00\x00\x
00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00
\x00\x00\x00\x00\x00\
x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00
\x00\x00\x00
...many more lines of junk...'
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>Comment By: Skip Montanaro (montanaro)
Date: 2006-10-07 05:38
Message:
Logged In: YES
user_id=44345
Works for me. (Nearly current build from SVN.) I find it implausible that your
explanation of failing to flush the file is the cause of the problem since
closing
the file will cause it to be flushed. You didn't open the file for "w+" so
there's no
opportunity to switch between writing and reading.
What platform are you using?
----------------------------------------------------------------------
Comment By: andrei kulakov (rainy)
Date: 2006-10-03 20:23
Message:
Logged In: YES
user_id=511010
Python newsgroup folks said that this is normal because when
switching between write/read modes without doing flush()
first, result is undefined. There was a suggestion from
Terry Ready to add this to documentation on file methods:
"When switching from reading or writing (or vice versa),
call flush(), or
the result will be undefined."
thx, -andrei
----------------------------------------------------------------------
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