[Tutor] Looking up a value in a dictionary from user input problem

[Dave Angel]

chase pettet wrote:
> I am trying to write a script to work our LVS implementation.  I want to be
> able to have  user do something like this "./script SITE SERVER" and have
> the script look up the ip value of the site on that server and issue the
> command to pull the status from LVS.  I am almost there but for some reason
> when I try to pass the site parameter dynamically (the name of the
> dictionary) I keep getting errors about value type.  I have two example that
> work where the dictionary name is hard coded to to speak in the script, and
> the value I want to pull is dynamic using sys.argv[1], and one where I'm
> trying to pass the dictionary name and it does not work.  I tried to slim
> thse examples down, so hopefully they are helpful:
>
> ----<snip first two versions>-----
>
>
> Not working...
>
> ./script.py t site
>
> #!/usr/bin/env python
> site = {"l":"10.1.1.1", "t":"10.1.1.2", "x":"10.1.1.3", "s1":"10.1.1.4",
> "s2":"10.1.1.5", "s3":"10.1.1.6"}
>
> def runBash(cmd):
>   p = subprocess.Popen(cmd, shell=True, stdout=subprocess.PIPE)
>   out = p.stdout.read().strip()
>   return out
>
> class LVS_Site:
>   def show(self, site):
>     showsite = "ipvsadm -L -t %s:443" % (site)
>     showsiteresult = runBash(showsite)
>     return showsiteresult
>
> a = LVS_Site()
> z = sys.argv[2]
> b = b["%s" % (sys.argv[1])]
> c = a.show(b)
> print ""
> print ""
> print ""
> print c
>
> Error:
>
> Traceback (most recent call last):
>   File "./python2.py", line 22, in ?
>     b = z["%s" % (sys.argv[1])]
> TypeError: string indices must be integers
>
>
> I don't understand why the third one does not work. Thanks for any help!
>
>   
You didn't post the exact code, as the line that gives the error is 
quoted differently than it is.  I suspect that the error message shows 
the version you actually tested.

a = LVS_Site()
z = sys.argv[2]
                 at this point, z is a string, containing the characters 
"site"

b = z["%s" % (sys.argv[1])]

                 at this point, sys.argv[1] is a string, containing the 
character "t"
                 So  "s" % "t"    is a string, containing the character "t"
                 So you're trying to evaluate
                    "site"["t"]
And thus the error.  Strings can be indexed only by integers, not by 
characters.

It appears you're confusing the variable site with the string "site".   
The former is a dictionary, the latter is a string.

Now, you could lookup that string in the current global namespace, and 
get the dictionary with that name.  Something like (untested):

    b = globals().get(z, None) [ "%s" % (sys.argv[1])]

But this is pretty dangerous territory.  Perhaps if you tell us what 
you're actually trying to achieve, we might be able to help.  For 
example, you might have a limited list of dictionaries, and want the 
user to be able to choose among them by keyword.


    

site_HQ = {"l":"10.1.1.1", "t":"10.1.1.2", "x":"10.1.1.3", "s1":"10.1.1.4",
"s2":"10.1.1.5", "s3":"10.1.1.6"}

site_Alternate = {"l":"10.1.1.1", "t":"10.1.1.2", "x":"10.1.1.3", "s1":"10.1.1.4",
"s2":"10.1.1.5", "s3":"10.1.1.6"}

site_desperate = {"l":"10.1.1.1", "t":"10.1.1.2", "x":"10.1.1.3", 
"s1":"10.1.1.4",

"s2":"10.1.1.5", "s3":"10.1.1.6"}

sitelist = {"HQ":site_HQ, "Alternate", site_Alternate, 
"desperate":site_desperate}

b =  sitelist[sys.argv[2]] ["%s" % (sys.argv[1])]


DaveA