Appending to []

[Kiuhnm]

On 4/22/2012 10:29, Bernd Nawothnig wrote:
[...]
> In general I always prefer the pure functional approach. But you are
> right, if it is too costly, one has to weigh the pros and contras.

Here's some stupid trick I came up with after reading this thread. It's 
of very limited use, of course and I don't even know whether it's 
reliable or not.

-->
import sys

class MyList:			        # just a test
     def __init__(self, iter):
         self.__start_cnt = sys.getrefcount(self)
         self.__elems = list(iter)

     def __add__(self, other):
         global optimizations
         cnt = sys.getrefcount(self)
         if cnt == self.__start_cnt and len(self.__elems) > 100:
             print('optimized')
             optimizations += 1
             self.__elems.extend(other.__elems)
             return self
         print('normal behavior')
         return MyList(self.__elems + other.__elems)

     def __eq__(self, other):
         return self.__elems == other.__elems

     def __iter__(self):
         return self.__elems.__iter__()

optimizations = 0

print('#1')
y = MyList([1000, 1001])
x = MyList(range(0, 1000)) + y
assert x == MyList(range(0, 1002))
assert optimizations == 1

optimizations = 0

print('#2')
x = MyList(range(0, 1000))
z = x + MyList([1000, 1001])
assert x == MyList(range(0, 1000))
assert z == MyList(range(0, 1002))
assert optimizations == 0

optimizations = 0

print('#3')

def comp_list(from_, to_):
     # Some long computation which results in a list.
     return MyList(range(from_, to_))

x = comp_list(0, 1000) + comp_list(1000, 2000) + MyList([2000, 2001])
assert x == MyList(range(0, 2002))
assert optimizations == 2
<--

Kiuhnm