python - Pythonic way to check if a package is installed or not

Question

Pythonic way to check list of packages installed in Centos/Redhat?

In a bash script, I'd do:

 rpm -qa | grep -w packagename

Answer 1

import sys
import rpm

ts = rpm.TransactionSet()
mi = ts.dbMatch( 'name', sys.argv[1] )
try :
    h = mi.next()
    print "%s-%s-%s" % (h['name'], h['version'], h['release'])
except StopIteration:
    print "Package not found"

1. TransactionSet() will open the RPM database
2. dbMatch with no paramters will set up a match iterator to go over the entire set of installed packages, you can call next on the match iterator to get the next entry, a header object that represents one package

3. dbMatch can also be used to query specific packages, you need to pass the name of a tag, as well as the value for that tag that you are looking for:

   dbMatch('name','mysql')