bartc wrote:
> On 24/05/2017 16:41, Peter Otten wrote:
>> Dennis Lee Bieber wrote:
>>
>>> On Tue, 23 May 2017 21:42:45 +0100, bartc <b...@freeuk.com> declaimed the
>>> following:
>>>
>>>> Is it necessary to sort them? If XXX is known, then presumably the
>>>> first file will be called XXX_chunk_0, the next XXX_chunk_1 and so on.
>>>>
>>>
>>> XXX_chunk_1
>>> XXX_chunk_10
>>> XXX_chunk_2
>>
>> This is a problem you run into if you do sort the filenames (the wrong
>> way, alphabetically). If I understand Bart correctly he suggests
>> something like
>>
>> with open(DESTFILE, "wb") as outstream:
>> for filename in map("XXX_chunk_{}".format, itertools.count()):
>> try:
>> with open(filename, "rb") as instream:
>> shutil.copyfileobj(instream, outstream)
>> except FileNotFoundError:
>> break
>>
>
> Yes, that sort of thing, provided the first file end with _0, XXX is
> known, and the endings are consecutive and well-formed. I was going to
> post some code but wasn't sure how 'with' dealt with file errors:
>
> i = 0
>
> while 1:
> file = "XXX_chunk_"+str(i)
> print (file)
> with open(file) as inf:
> ....
> i += 1
Inside the with suite the author of the context manager gets to decide.
E. g. you may decide to swallow everyhing:
>>> from contextlib import contextmanager
>>>
>>> @contextmanager
... def catch():
... try: yield
... except: pass
...
>>> with catch(): 1/0
...
>>>
For whatever open() returns the reaction is to close the file and propagate
the error:
>>> with open("/dev/null", "rb") as f: 1/0
...
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
ZeroDivisionError: division by zero
>>> f.closed
True
However, in the case of a failing open() the file's __enter__ method is not
yet called and so the behaviour is the same as for the conventional
inf = open(file)
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