En Sat, 21 Mar 2009 23:58:07 -0300, <lamber...@corning.com> escribió:
'''
A python 3 question.
Presume this code is in file p.py.
The program fails.
$ python3 p.py
...
ValueError: I/O operation on closed file.
Removing the comment character to increase the stream
reference count fixes the program, at the expense of
an extra TextIOWrapper object.
Please, what is a better way to write the class with
regard to this issue?
'''
import re
import io
class file(io.TextIOWrapper):
'''
Enhance TextIO. Streams have many sources,
a file name is insufficient.
'''
def __init__(self,stream):
#self.stream = stream
super().__init__(stream.buffer)
print(file(open('p.py')).read())
You're taking a shortcut (the open() builtin) that isn't valid here.
open() creates a "raw" FileIO object, then a BufferedReader, and finally
returns a TextIOWrapper. Each of those has a reference to the previous
object, and delegates many calls to it. In particular, close() propagates
down to FileIO to close the OS file descriptor.
In your example, you call open() to create a TextIOWrapper object that is
discarded as soon as the open() call finishes - because you only hold a
reference to the intermediate buffer. The destructor calls close(), and
the underlying OS file descriptor is closed.
So, if you're not interested in the TextIOWrapper object, don't create it
in the first place. That means, don't use the open() shortcut and build
the required pieces yourself.
---
There is another alternative that relies on undocumented behaviour: use
open to create a *binary* file and wrap the resulting BufferedReader
object in your own TextIOWrapper.
import io
class file(io.TextIOWrapper):
def __init__(self, buffer):
super().__init__(buffer)
print(file(open('p.py','rb')).read())
--
Gabriel Genellina
--
http://mail.python.org/mailman/listinfo/python-list
