Search for ``what`` in the iterable ``data`` and return the index of the 
    first match. Return ``None`` if no match found.

def find_first(data, what):
    '''
    Search for ``what`` in the iterable ``data`` and return the index of the 
    first match. Return ``None`` if no match found.
    '''
    for i, line in enumerate(data):
        if contains(line, what):
            return i
            
    return None