problem with if then

[Jean Dubois]

On 9 jun, 22:23, Roy Smith <r... at panix.com> wrote:
> In article
> <cd1be83a-f560-4024-90b3-697a51bb1... at g7g2000vbv.googlegroups.com>,
>  Jean Dubois <jeandubois... at gmail.com> wrote:
>
> > I'm writing some code to check whether an url is available or not,
> > therefore I make use of a wget-command in Linux and then check whether
> > this is successful
>
> In general, "shelling out" to run a command-line utility should be the
> last resort.  It's slower, and more complicated, than doing it in pure
> python.  You would only call a shell command if there was no other way.
>
> Fortunately, in Python, there is another way.  Several, in fact.
>
> The most straight-forward is to use the built-in urllib2 module
> (http://docs.python.org/2/library/urllib2.html).
>
> If you're going to be doing anything complicated (i.e. setting optional
> headers, managing cookies, etc), you probably want to be looking at the
> excellent third-party module, requests (http://python-requests.org).
>
> In any case, given your code:
>
>
>
>
>
>
>
>
>
> > #!/usr/bin/env python
> > import sys
> > import os
> > from datetime import datetime, timedelta
> > today=datetime.now()
> > yesterday= datetime.now() - timedelta(days=1)
> > daybeforeyesterday= datetime.now() - timedelta(days=2)
> > collection = [daybeforeyesterday,yesterday,today]
> > for thisday in collection:
> >      checkavailablestring='wget -q -O -
> >http://www.deredactie.be/cm/vrtnieuws/videozone/programmas/journaal/E...
> > ay.strftime("%y%m%d")+'_JO7
> > >/dev/null ; echo $?'
> >      if os.system(checkavailablestring)==0:
> >           print thisday, 'stream is available'
> >      else:
> >           print thisday, 'stream is not available'
>
> I would break the debugging down into several parts.  First, are you
> generating the command string properly?  Try printing out
> checkavailablestring before you call os.system() to make sure it's what
> you think it is.
>
> Next, once you're sure you've got the correct string, run it manually in
> the shell and see what it does.
>
> Next, are you sure you're using os.system() correctly?  Try running:
>
> os.system("/bin/true")
>
> and
>
> os.system("/bin/false")
>
> and make sure you get the results you think you should.  But, really,
> once you've done all that (and it's worth doing as an exercise), rewrite
> your code to use urllib2 or requests.  It'll be a lot easier.

Could you show me how to code the  example in metacode below wuth the
use of urllib2?
#!/usr/bin/env python
import urllib2
if check whether url exists succeed:
    print 'url exists'
else:
    print 'url does not exist'

thanks in advance
jean