def scroll_left(w, size, key):
    self.source_hscroll_start = max(0, (self.source_hscroll_start - 4))
    for sl in self.source:
        sl._invalidate()
def scroll_left(w, size, key):
    self.source_hscroll_start = max(0, (self.source_hscroll_start - 4))
    for sl in self.source:
        sl._invalidate()