casting - Why is calling float() on a number slower than adding 0.0 in Python? -

what reason casting integer float slower adding 0.0 int in python?

import timeit   def add_simple():     in range(1000):         = 1 + 0.0   def cast_simple():     in range(1000):         = float(1)   def add_total():     total = 0     in range(1000):         total += 1 + 0.0   def cast_total():     total = 0     in range(1000):         total += float(1)   print "add simple timing: %s" % timeit.timeit(add_simple, number=1) print "cast simple timing: %s" % timeit.timeit(cast_simple, number=1) print "add total timing: %s" % timeit.timeit(add_total, number=1) print "cast total timing: %s" % timeit.timeit(cast_total, number=1) 

the output of is:

add simple timing: 0.0001220703125

cast simple timing: 0.000469923019409

add total timing: 0.000164985656738

cast total timing: 0.00040078163147

if use dis module, can start see why:

in [11]: dis.dis(add_simple)   2           0 setup_loop              26 (to 29)               3 load_global              0 (range)               6 load_const               1 (1000)               9 call_function            1 (1 positional, 0 keyword pair)              12 get_iter         >>   13 for_iter                12 (to 28)              16 store_fast               0 (i)    3          19 load_const               4 (1.0)              22 store_fast               1 (a)              25 jump_absolute           13         >>   28 pop_block         >>   29 load_const               0 (none)              32 return_value  in [12]: dis.dis(cast_simple)   2           0 setup_loop              32 (to 35)               3 load_global              0 (range)               6 load_const               1 (1000)               9 call_function            1 (1 positional, 0 keyword pair)              12 get_iter         >>   13 for_iter                18 (to 34)              16 store_fast               0 (i)    3          19 load_global              1 (float)              22 load_const               2 (1)              25 call_function            1 (1 positional, 0 keyword pair)              28 store_fast               1 (a)              31 jump_absolute           13         >>   34 pop_block         >>   35 load_const               0 (none)              38 return_value 

note call_function

function calls in python (relatively) slow. . lookups. because casting float requires function call - that's why it's slower.