在Python 2.7中循环数据

Question

I am trying to detect phase times for an oscillating object, but I can't seem to figure out how to keep my previous three data points stored at all times.

prev2 == prev
prev == current
current == int(data)

Every time I go through a data collection loop, I get some value for data, and I expect if I go through this loop 3 times, I should have my previous three values for data stored as my variables, but for some reason current, prev, and prev2 all stay at 0. What makes even less sense to me, is that if I put: print(int(data)) directly below all of this, it will return the number I want to go into current. If anyone would know how I could fix this, I would greatly appreciate it.

Answer 1

You want to use = instead of == . == checks for equality while = is an assignment statement. Your code should be:

prev2 = prev
prev = current
current = int(data)

Answer 2

This is an excellent opportunity to introduce you to the deque .

>>> from collections import deque
>>>
>>> rolling = deque([5,6,7], maxlen=3)
>>> rolling
deque([5, 6, 7], maxlen=3)
>>> rolling.append(8)
>>> rolling
deque([6, 7, 8], maxlen=3)