[Tutor] about pyhton + regular expression

[Paul Tremblay]

On Thu, Mar 20, 2003 at 09:41:01AM -0800, Jeff Shannon wrote:
> 
> It should also be noted that, in both new and older versions of Python, 
> there's a special pseudo-iterator that can be used.  If you use the 
> standard idiom
> 
> infile = open('file.txt')
> for line in infile.readlines():
>    [...]
> infile.close()
> 
> then the entire contents of the file is read into a list of lines.  If 
> the file is large, this may swamp available memory.  You can use the 
> special xreadlines() method instead --
> 
> for line in infile.xreadlines():
>    [...]
> 

Nifty. I had been doing:

line_to_read = '1'
while line_to_read:
    line_to_read = infile.readline()

> destroyed right away when the last reference for them is deleted -- it 
> happens right away in the current implementation of CPython, but not in 
> Jython, and it's not guaranteed in *any* implementation.  Typically, 
> with files that are read once and never written to, this won't matter 
> much, but if you're reading in a file and then later writing to the same 
> file, it could cause problems.  I feel that it's a good habit to 
> explicitly close files, whether strictly necessary or not, so that I 
> don't have to worry about which circumstances may be problematic and 
> which are safe.


I strongly second this. Even in CPython I have had problems when I
didn't close a file:

file_obj.close

I had meant to close the file, but forgot the parenthesis, and couldn't
figure out for the life of me why the rest of the program didn't work.

Paul

-- 

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*Paul Tremblay         *
*phthenry@earthlink.net*
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