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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def whitespace_before_cursor_on_line():
 """ Filter which evaluates to True when the characters before the cursor are whitespace, or we are at the start of te line. """

    b = get_app().current_buffer
    before_cursor = b.document.current_line_before_cursor

    return bool(not before_cursor or before_cursor[-1].isspace())