Array? Please help.

[Scott David Daniels]

Scott David Daniels wrote:
> Dr. Pastor wrote:
>> Scott David Daniels wrote:
>>> Dr. Pastor wrote:
>>>> I need a row of 127 bytes that I will use as a
>>>> circular buffer. Into the bytes (at unspecified times)
>>>> a mark (0<mark<128) will be written, one after the other.
>>>> After some time the "buffer" will contain the last 127 marks.
>>> Sounds a lot like homework.
>> No it is not home work.
> 
> OK, taking you at your word, here's one way:
>  (and some untested code)

As penance for posting untested code, here is a real implementation:

     import array

     class Circular(object):
         '''A circular buffer, holds only non-zero entries'''
         def __init__(self, size=127):
             '''Create as N-long circular buffer

             .data is the circular data store.
             .point is the index of the next value to write
             '''
             self.data = array.array('b', [0] * size)
             self.point = 0

         def mark(self, value):
             '''Add a single value (non-zero) to the buffer'''
             assert value
             self.data[self.point] = value
             self.point += 1
             if self.point >= len(self.data):
                 self.point = 0

         def recent(self):
             '''Return the most recent values saved.'''
             result = self.data[self.point :] + self.data[: self.point]
             for n, v in enumerate(result):
                 if v:
                     return result[n :]
             return result[: 0] # an empty array

Tests:
     c = Circular(3)
     assert list(c.recent()) == []
     c.mark(12)
     assert list(c.recent()) == [12]
     c.mark(11)
     assert list(c.recent()) == [12, 11]
     c.mark(10)
     assert list(c.recent()) == [12, 11, 10]
     c.mark(9)
     assert list(c.recent()) == [11, 10, 9]


--Scott David Daniels
scott.daniels at acm.org