Using plugins (e.g. custom types, facts, functions and providers) gives you even more control over the behaviour of puppet and extend what it can do. An example custom fact that exposes the version of Python installed is:

# From http://reductivelabs.com/trac/puppet/wiki/Recipes/PythonVersion
require 'facter'

pythonversion = nil
if FileTest.exists?("/usr/bin/python")
    pythonversion = %x{python -V 2>&1}.split(" ")[1]
end

Facter.add("pythonversion") do
    setcode do
        pythonversion
    end
end

Facter.add("pythonmmversion") do
    pythonmmversion = nil
    if pythonversion != nil
        pythonversionsplit = pythonversion.split(".")
        pythonmmversion = pythonversionsplit[0] + "." + pythonversionsplit[1]
    end
    setcode do
        pythonmmversion
    end
end

Using this new custom fact you can create conditional statements in manifests or templates using $pythonverion or $pythonmmversion.