file corruption on windows - possible bug

[Jeremy Jones]

Fredrik Lundh wrote:

>Jeremy Jones wrote:
>
>  
>
>>#################################
>>file_dict = {}
>>
>>a_list = [("a", "a%s" % i) for i in range(2500)]
>>b_list = [("b", "b%s" % i) for i in range(2500)]
>>c_list = [("c", "c%s" % i) for i in range(2500)]
>>d_list = [("d", "d%s" % i) for i in range(2500)]
>>
>>
>>joined_list = a_list + b_list + c_list + d_list
>>
>>for key, value in joined_list:
>>   outfile = file_dict.setdefault(key, open("%s.txt" % key, "w"))
>>    
>>
>
>you do realize that this opens the file again every time, so you end up having
>4x2500 file handles pointing to 4 physical files.  that's a bad idea.
>  
>
That *is* a bad idea, and no, I didn't realize that would be the result.
>From the "mapping types" page:

|a.setdefault(k[, x])| 	|a[k]| if |k in a|, else x (also setting it) 	(5)


*(5)*
    setdefault() is like get(), except that if k is missing, x is both
    returned and inserted into the dictionary as the value of k. x
    defaults to None.


I took this to mean that setdefault was a short-circuit and only created
the default object once if the dictionary didn't contain the specified
key. But I guess it's *me* who is passing setdefault a new file handle a
few thousand times :-) Ouch.

>if you replace
>
>    outfile = file_dict.setdefault(key, open("%s.txt" % key, "w"))
>
>with
>
>    outfile = file_dict.get(key)
>    if outfile is None:
>        file_dict[key] = outfile = open("%s.txt" % key, "w")
>
>or, if you prefer,
>
>    try:
>        outfile = file_dict[key]
>    except KeyError:
>        file_dict[key] = outfile = open("%s.txt" % key, "w")
>
>your code won't depend on any undefined behaviour, and will work properly
>on all platforms.
>
></F> 
>
>
>
>  
>
Thanks (and thanks to you, Duncan, for your reply as well),


Jeremy
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