Finding the first active ethernet interface with ansible

eth.py

def first_eth(v, **kw):
    '''Finding the first active ethernet interface'''
    for n in range(10):
        name = 'ansible_eth%i' % n
        if name not in v:
            return
        eth = v[name]
        if eth['active']:
            return eth


class FilterModule(object):
    def filters(self):
        return dict(first_eth=first_eth)

You need a setting in your ansible.cfg :

[defaults]
filter_plugins = ./filter_plugins