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Hello,

I read some files name from a directory and then I put these name in a
list. I will check whether it is empty or not, and I would do it with
an exception. With if statement it is very simple:

If list_of_files != "" : # this can be if list_of_files !=
[]:
get the files
elas:
there is no file

But with exception, I can write something as:

try:
list_of_files != []
get the files
except ValueError:
Print " there is no file"

What can the first statement be inside 'try' if I don't want to use if
statement?
Maybe my understandig of exception is enough to got it.

Would somebody explain me about this?

Regards,
Nader


try and except in a dircMaybe this quetion will be simple enough for
you.

En Fri, 13 Jun 2008 04:37:44 -0300, Nader <> escribió:

> Hello,
>
> I read some files name from a directory and then I put these name in a
> list. I will check whether it is empty or not, and I would do it with
> an exception. With if statement it is very simple:
>
> If list_of_files != "" : # this can be if list_of_files !=
> []:
> get the files
> elas:
> there is no file

If it is simple, just do it! Why do you want to make things more
complicated? This would be enough:

if list_of_files:
get_the_files(list_of_files)
else:
print "there is no file"

(a list has a false boolean value when it is empty)

> But with exception, I can write something as:
>
> try:
> list_of_files != []
> get the files
> except ValueError:
> Print " there is no file"
>
> What can the first statement be inside 'try' if I don't want to use if
> statement?

If you insist on using an exception (and assuming list_of_files is
actually a list, not a string or other kind of sequence):

try:
list_of_files[0]
except IndexError:
...no files...

This way you're checking that list_of_files contains at least one element.
But I would not reccomend it.

--
Gabriel Genellina

On Jun 13, 11:34 am, "Gabriel Genellina" <gagsl-...@yahoo.com.ar>
wrote:
> En Fri, 13 Jun 2008 04:37:44 -0300, Nader <n.em...@gmail.com> escribió:
>
> > Hello,
>
> > I read some files name from a directory and then I put these name in a
> > list. I will check whether it is empty or not, and I would do it with
> > an exception. With if statement it is very simple:
>
> > If list_of_files != "" : # this can be if list_of_files !=
> > []:
> > get the files
> > elas:
> > there is no file
>
> If it is simple, just do it! Why do you want to make things more
> complicated? This would be enough:
>
> if list_of_files:
> get_the_files(list_of_files)
> else:
> print "there is no file"
>
> (a list has a false boolean value when it is empty)
>
> > But with exception, I can write something as:
>
> > try:
> > list_of_files != []
> > get the files
> > except ValueError:
> > Print " there is no file"
>
> > What can the first statement be inside 'try' if I don't want to use if
> > statement?
>
> If you insist on using an exception (and assuming list_of_files is
> actually a list, not a string or other kind of sequence):
>
> try:
> list_of_files[0]
> except IndexError:
> ...no files...
>
> This way you're checking that list_of_files contains at least one element.
> But I would not reccomend it.
>
> --
> Gabriel Genellina

I would accept your suggestion in raltion of checking a list whether
it is empty or not with "if" statement. It is more expressive and
clear. But In this case I would learn more about the "try .... except"
exception.

Nader

On 15:37, venerdì 13 giugno 2008 Nader wrote:

> try:
> list_of_files != []
> get the files
>
For file in list_of_files:
try:
myfile = open(file, 'r')
except (IOError, OSError):
print"Your %s file wasn't open" %file
# here you can do something with your open file as read option
myfile.readlines() # for example
--
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