In ruby, the equivalent to try...except is begin...rescue. In the
rescue section you can ask it to retry the begin section. So, for
example:
b=0
begin
puts 1/b
rescue
b=1
retry # <- this little guy
end
Well, it's all a matter of how you look at it. I personally
prefer to see that there's some sort of looping going on.
Something crazy like this contrived example, it would be best to
just check to see if b==0 beforehand. However, for the sake of
example, one could do something like
b = 0
for d in [b, 1]:
try:
print 1/d
break
except ZeroDivisionError:
pass
which would allow you to have a number of things to try...to give
a little more plausibility to the idea, the original ruby might
have been something like (forgive my ignorance of ruby syntax)
url = 'http://www.example.com'
begin
get_webpage(url)
rescue
url = 'http://www2.example.com'
retry
end
which would try a backup server if the main one is down. The
above python variant would allow an arbitrary number of servers
to be listed
servers = ['http://www%i.example.com' % i for i in xrange(1,5)]
for server in servers:
try:
u = urllib.urlopen(server)
break
except IOError:
pass
else:
raise NoAvailableServersException()
This comes full-circle on another thread asking about the use of
"else:" after a for/while loop...yes, nice to have.
The above python code will try to open each of the servers in
turn until it gets one that it can open. If it can't open any of
them, it raises some concocted NoAvailableServersException. To
get the above to succeed, you can add
servers[3] = 'http://www.example.com'
which will actually exist, and thus will fall out of the loop
with "u" successfully set to the connection from which you can read.
I have to agree with Diez, that this sounds like some
ambiguous/dangerous behaviour could ensue from such a language
construct. I'd just as soon specify my desired behavior explicitly.
Just a few ideas.
-tkc
