get_term_by not working when in functions.php

I have an odd issue with get_term_by(). It’s working fine when I use it inside a template, but when I use it in functions.php it just returns false.

$term = get_term_by('slug', 'some-term', 'some-taxonomy');
var_dump($term);

Any explanation as to why this is happening would be greatly appreciated.

This is probably happening because the taxonomy you’re trying to query is registered yet. Eg. The WordPress environment is loaded when a theme’s functions.php file loads, but many plugins/themes/core functions don’t register taxonomies until later.

Try hooking into init with a really high priority number and running the get_term_by function. Like so:

<?php
add_action( 'init', 'wpse27111_tester', 999 );
function wpse27111_tester()
{
    $term = get_term_by('slug', 'some-term', 'some-taxonomy');
    var_dump($term);
}