generators vs lists

gistfile1.py

[] tadas@tadascb-2 ~/tmp: cat generators.py
def munge(i):
    return i ** 2 + i

def func1():
    return ( munge(i) for i in xrange(10) )

def func2():
    return [ munge(i) for i in xrange(10) ]

if __name__ == '__main__':
    print list(func1())
    print func2()
[] tadas@tadascb-2 ~/tmp: python
Python 2.7.1 (r271:86832, Jul 31 2011, 19:30:53)
[GCC 4.2.1 (Based on Apple Inc. build 5658) (LLVM build 2335.15.00)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import dis
>>> import generators
>>> dis.dis(generators.func1)
  5           0 LOAD_CONST               1 (<code object <genexpr> at 0x109edb3b0, file "generators.py", line 5>)
              3 MAKE_FUNCTION            0
              6 LOAD_GLOBAL              0 (xrange)
              9 LOAD_CONST               2 (10)
             12 CALL_FUNCTION            1
             15 GET_ITER
             16 CALL_FUNCTION            1
             19 RETURN_VALUE
>>> dis.dis(generators.func2)
  8           0 BUILD_LIST               0
              3 LOAD_GLOBAL              0 (xrange)
              6 LOAD_CONST               1 (10)
              9 CALL_FUNCTION            1
             12 GET_ITER
        >>   13 FOR_ITER                18 (to 34)
             16 STORE_FAST               0 (i)
             19 LOAD_GLOBAL              1 (munge)
             22 LOAD_FAST                0 (i)
             25 CALL_FUNCTION            1
             28 LIST_APPEND              2
             31 JUMP_ABSOLUTE           13
        >>   34 RETURN_VALUE
>>> from timeit import Timer
>>> t1 = Timer(generators.func1)
>>> t2 = Timer(generators.func2)
>>> t1.timeit()
0.8525791168212891
>>> t2.timeit()
3.2556989192962646