[SciPy-user] probably a stupid question: MatLab equivalent of "diff" ?

Does anyone know the equivalent of the MatLab "diff" function. The "diff" functions calculates the difference between 2 succeeding elements of an array. I need to detect (fast) the falling edge of a binary signal. There's derivate function in Python diff, but when you use an binary (true/false) input, it also detects rising edges. Probably a stupid question, but I still have troubles, digging to huge amount of information about Python. thanks, Stef Mientki