Returns an iterator pointing to the position of the first item found equal to data according to cmp_func and cmp_data. If more than one item is equal, it is not guaranteed that it is the first which is returned. In that case, you can use Sequence.iterNext and Sequence.iterPrev to get others.
cmp_func is called with two items of the seq, and cmp_data. It should return 0 if the items are equal, a negative value if the first item comes before the second, and a positive value if the second item comes before the first.
This function will fail if the data contained in the sequence is unsorted.
data to look up
the function used to compare items in the sequence
user data passed to cmp_func
an glib.SequenceIter pointing to the position of the first item found equal to data according to cmp_func and cmp_data, or NULL if no such item exists