"file" does not work with the "with" statement!
Michele Simionato
with file(name, 'w') as f:
do_something(f)
does not close the file at the end of the with statement! On the
contrary
with open(name, 'w') as f:
do_something(f)
works fine. The docs say "When opening a file, it’s preferable to use
open() instead of invoking this constructor directly." but perhaps
they should mention why :(
Peter Otten
Are you sure?
Python 2.6.4 (r264:75706, Nov 2 2009, 14:44:17)
[GCC 4.4.1] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> with file("tmp.txt", "w") as f:
... print >> f, "whatever"
...
>>> f.write("something")
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
ValueError: I/O operation on closed file
Peter
Diez B. Roggisch
Are you sure? For me on python2.5, it works as advertised:
from __future__ import with_statement
def test(outf):
with outf:
outf.write("test\n")
try:
outf.write("test\n")
assert False, "Not closed"
except ValueError:
pass
outf = open("/tmp/foo", "w")
test(outf)
outf = file("/tmp/bar", "w")
test(outf)
Which Python do you use?
Diez
Michele Simionato
> Are you sure? For me on python2.5, it works as advertised:
>
> from __future__ import with_statement
>
> def test(outf):
> with outf:
> outf.write("test\n")
> try:
> outf.write("test\n")
> assert False, "Not closed"
> except ValueError:
> pass
>
> outf = open("/tmp/foo", "w")
> test(outf)
> outf = file("/tmp/bar", "w")
> test(outf)
>
> Which Python do you use?
>
> Diez
Python 2.5, but it could be an artifact of the way I am looking if a
file is closed.
I have subclassed the file builtin, added a .close method and it was
not called by the
"with" statement. This during debugging, but now I have found another
reason to explain why I was
running out of file descriptors, (I was opening too many connections
to the db).
It is entirely possible that the problem was not with the "with"
statement.
Diez B. Roggisch
> On Dec 10, 11:04 am, "Diez B. Roggisch" <de...@nospam.web.de> wrote:
>> Are you sure? For me on python2.5, it works as advertised:
>>
>> from __future__ import with_statement
>>
>> def test(outf):
>> with outf:
>> outf.write("test\n")
>> try:
>> outf.write("test\n")
>> assert False, "Not closed"
>> except ValueError:
>> pass
>>
>> outf = open("/tmp/foo", "w")
>> test(outf)
>> outf = file("/tmp/bar", "w")
>> test(outf)
>>
>> Which Python do you use?
>>
>> Diez
>
> Python 2.5, but it could be an artifact of the way I am looking if a
> file is closed.
The above ran on python2.5 for me, no hitch.
> I have subclassed the file builtin, added a .close method and it was
> not called by the
> "with" statement. This during debugging, but now I have found another
> reason to explain why I was
> running out of file descriptors, (I was opening too many connections
> to the db).
> It is entirely possible that the problem was not with the "with"
> statement.
Probably. Closing a file through with might not involve calling close() - it
might be implemented differently in __exit__.
So overload *that*, too.
Diez
Peter Otten
Subclassing file doesn't work properly:
http://mail.python.org/pipermail/python-list/2005-April/920562.html
Peter
Christian Heimes
> Python 2.5, but it could be an artifact of the way I am looking if a
> file is closed.
> I have subclassed the file builtin, added a .close method and it was
> not called by the
> "with" statement. This during debugging, but now I have found another
> reason to explain why I was
> running out of file descriptors, (I was opening too many connections
> to the db).
> It is entirely possible that the problem was not with the "with"
> statement.
In Python 2.5 you have to implement your own __enter__ and __exit__
methods if you subclass from file. The file.__exit__ function doesn't
call f.close(). The minor inconsistency has been fixed in Python 2.6.
Python 2.5:
static PyObject *
file_exit(PyFileObject *f, PyObject *args)
{
PyObject *ret = file_close(f);
if (!ret)
/* If error occurred, pass through */
return NULL;
Py_DECREF(ret);
/* We cannot return the result of close since a true
* value will be interpreted as "yes, swallow the
* exception if one was raised inside the with block". */
Py_RETURN_NONE;
}
Python 2.6:
static PyObject *
file_exit(PyObject *f, PyObject *args)
{
PyObject *ret = PyObject_CallMethod(f, "close", NULL);
if (!ret)
/* If error occurred, pass through */
return NULL;
Py_DECREF(ret);
/* We cannot return the result of close since a true
* value will be interpreted as "yes, swallow the
* exception if one was raised inside the with block". */
Py_RETURN_NONE;
}
Michele Simionato
> In Python 2.5 you have to implement your own __enter__ and __exit__
> methods if you subclass from file. The file.__exit__ function doesn't
> call f.close().
Yes, that was my problem.