Determine if package installed with Yum Python API

Question

TLDR; I need simple a Python call given a package name (e.g., 'make') to see if it's installed; if not, install it (I can do the latter part).

Problem:

So there are a few code examples given in http://yum.baseurl.org/wiki/YumCodeSnippets, but other than kludging around inside ipython and guessing at what each method does, there doesn't appear to be any actual documentation for the Python API for yum. It's apparently all tribal knowledge.

[edit] Apparently I just accidentally discovered the API documentation (after receiving an acceptable answer, of course). It's not linked from the main page, but here it is for future reference: http://yum.baseurl.org/api/yum/

What I need to do:

I have a deployment configuration script that relies on other system packages (make, gcc, etc.). I know I can install them like this: http://yum.baseurl.org/wiki/YumCodeSnippet/SimplestTransaction but I'd like to have the option to query if they're already installed before doing so, so I can have the additional option of simply failing if the packages aren't present instead of forcing installation. What's the proper call to do this (or better, has anyone actually bothered to properly document the API outside of code samples?)

I've never touched Python prior to this project, and I'm really liking it, but... some of the module documentation is more elusive than unicorn-riding leprechauns.

Answer 1

import yum

yb = yum.YumBase()
if yb.rpmdb.searchNevra(name='make'):
   print "installed"
else:
   print "not installed"

Answer 2

You could run 'which' on the subsystem to see if the system has the binaries you are looking for:

import os
os.system("which gcc")
os.system("which obscurepackagenotgoingtobefound")

Answer 3

For anyone who stumbles across this post later, here's what I came up with. Note that "testing" and "skip_install" are flags that I parse from the script invocation.

    print "Checking for prerequisites (Apache, PHP + PHP development, autoconf, make, gcc)"
    prereqs = list("httpd", "php", "php-devel", "autoconf", "make", "gcc")

    missing_packages = set()
    for package in prereqs:
        print "Checking for {0}... ".format([package]),

        # Search the RPM database to check if the package is installed
        res = yb.rpmdb.searchNevra(name=package)
        if res:
            for pkg in res:
                print pkg, "installed!"
        else:
            missing_packages.add(package)
            print package, "not installed!"
            # Install the package if missing
            if not skip_install:
                if testing:
                    print "TEST- mock install ", package
                else:
                    try:
                        yb.install(name=package)
                    except yum.Errors.InstallError, err:
                        print >> sys.stderr, "Failed during install of {0} package!".format(package)
                        print >> sys.stderr, str(err)
                        sys.exit(1)

    # Done processing all package requirements, resolve dependencies and finalize transaction
    if len(missing_packages) > 0:
        if skip_install:
            # Package not installed and set to not install, so fail
            print >> sys.stderr, "Please install the {0} packages and try again.".format(
                ",".join(str(name) for name in missing_packages))
            sys.exit(1)
        else:
            if testing:
                print "TEST- mock resolve deps and process transaction"
            else:
                yb.resolveDeps()
                yb.processTransaction()

Answer 4

import yum

yb = yum.YumBase()
yb.isPackageInstalled('make')