arrays - Arithmetic Progression in Python without storing all the values -

i'm trying represent array of evenly spaced floats, arithmetic progression, starting @ a0 , elements a0, a0 + a1, a0 + 2a1, a0 + 3a1, ... numpy's arange() method does, seems allocate memory whole array object , i'd using iterator class stores a0, a1 , n (the total number of elements, might large). exist in standard python packages? couldn't find so, ploughed ahead with:

class mylist():     def __init__(self, n, a0, a1):         self._n = n         self._a0 = a0         self._a1 = a1      def __getitem__(self, i):         if < 0 or >= self._n:             raise indexerror         return self._a0 + * self._a1      def __iter__(self):         self._i = 0         return self      def next(self):         if self._i >= self._n:             raise stopiteration         value = self.__getitem__(self._i)         self._i += 1         return value 

is sensible approach or revinventing wheel?

well, 1 thing doing wrong should for i, x in enumerate(a): print i, x.

also, i'd use generator method instead of hassle __iter__ , next() methods, because solution wouldn't allow iterate on same mylist twice @ same time 2 different iterators (as self._i local class).

this better solution gives random access efficient iterator. support in , len operators thrown in bonus :)

class mylist(object):     def __init__(self, n, a0, a1, eps=1e-8):         self._n = n         self._a0 = a0         self._a1 = a1         self._eps = eps      def __contains__(self, x):         y = float(x - self._a0) / self._a1         return 0 <= int(y) < self._n , abs(y - int(y)) < self._eps      def __getitem__(self, i):         if 0 <= < self._n:             return self._a0 + * self._a1         raise indexerror      def __iter__(self):         current = self._a0         in xrange(self._n):              yield current              current += self._a1      def __len__(self):         return self._n