[Tutor] Help with sys.argv

[Dave Angel]

On 01/-10/-28163 02:59 PM, monkey415 at aim.com wrote:
> Hello,
>
> I am trying to learn how to use python with Facebook's Open Graph API.  I am getting my feet wet with the following code authored by Matthew A. Russell.  I copied it line for line for learning purposes, but I am getting the following error:
>
> Traceback (most recent call last):
>    File "C:\Python27\Lib\site-packages\pythonwin\pywin\framework\scriptutils.py", line 325, in RunScript
>      exec codeObject in __main__.__dict__
>    File "C:\Python27\Scripts\facebook__query.py", line 20, in<module>
>      Q = sys.argv[1]
> IndexError: list index out of range
>
>
> Here is the code that this error is resulting from:
>
> #Querying the Open Graph for "programming" groups
>
> import sys
> import json
> import facebook
> import urllib2
> from facebook__login import login
>
> try:
>      ACCESS_TOKEN = open('C:\Users\Jon\Documents\FacebookApps\facebook.access_token').read()
> except IOError, e:
>      try:
>          #Page 283 in Mining... for notes
>          ACCESS_TOKEN = sys.argv[1]
>          Q = sys.argv[2]
>      except:
>          print>>  sys.stderr, \
>                "Could not either find access token in 'C:\Users\Jon\Documents\FacebookApps\facebook.access_token' or parse args."
>          ACCESS_TOKEN = login()
>          Q = sys.argv[1]
>
> LIMIT = 100
>
> gapi = facebook.GraphAPI(ACCESS_TOKEN)
> ...
> ...
>
>
> Clearly this has something to do with sys.argv[1], and I think I'm getting an IOError somewhere along the line.
>
> I have tried quite hard to figure this out on my own using the Python tutorial, Google, and the book in which the code was found to no avail.  Please help!
>
> Thanks,
> Jon
>
>
>
Usually, the first thing to do is to print sys.argv and see what it 
looks like.  If it has only one element in it, then you'd expect that 
sys.argv[1] would give exactly that error.   sys.argv[0] is the only 
element.

Next, look up argv in the Python docs.
See    http://docs.python.org/library/sys.html?highlight=argv#sys.argv

for a description.  In particular, if you didn't pass any arguments to 
the script, then argv will be of size 1, and you'll get the error you saw.

Fix is to add a check for len(sys.argv) to be greater than or equal to 
however many arguments you need, and display an error and exit if not.

DaveA