By using
(index for index, value in enumerate(the_iterable) if condition(value))
one can check the condition of the value of the first item in the_iterable, and obtain its index without the need to evaluate all of the items in the_iterable.
The complete expression to use is
first_index = next(index for index, value in enumerate(the_iterable) if condition(value))
Here first_index assumes the value of the first value identified in the expression discussed above.