The Cost of Dynamism (was Re: Pyhon 2.x or 3.x, which is faster?)

[BartC]

On 15/03/2016 11:52, BartC wrote:
> On 15/03/2016 01:55, Steven D'Aprano wrote:

>> switch obj:
>>      case "Hello", None: ...
>>      case [1, 2, 3]: ...
>>      case 23.01, 15+2j, Fraction(10, 11): ...
>>      case 100**100, {}: ...
>>
>>
>> and more. This is not negotiable: having a switch statement limited to
>> small
>> ints is simply not an option.
>
> Not a problem: http://pastebin.com/qdQintSZ

The solution I posted tested the values one after another. I was 
interested in whether it was that much faster than if-elif in CPython 3, 
so I tried the test similar to that below, except that k, c and f were 
literal values in the loop to start with.

Initial timings were 5 seconds for mine, 12.5 seconds for Python. That's 
in line with what I expected when dealing with more complex objects.

However, I then took the 100**100 outside the loop in my version (as 
that expression was not reduced to a constant). The timing then reduced 
to 170ms (I have a slow big num library).

But doing the same with Python made no difference. Taking Complex and 
Fraction outside reduced the timing to 8 seconds, still 50 times slower.

(My language doesn't understand Complex and Fraction, so testing against 
those is a quick process. Taking those out completely as well as 
100**100 made a difference, but there was the same discrepancy)

I know my language isn't that fast, so something is slowing down the 
Python in this test (and I don't /think/ I've left a zero out in my 
version!)

So maybe it makes the case for a proper Switch in Python stronger where 
such comparisons could be streamlined.


from fractions import Fraction

def test():
 
data=["Hello",None,[1,2,3],23.01,15+2j,Fraction(10,11),100**100,{},12345]
#    print (data)
     k=100**100
     c=15+2j
     f=Fraction(10,11)

     for n in range(100000):
         for obj in data:
             if obj=="hello" or obj==None:
                 pass
             elif obj==[1,2,3]:
                 pass
             elif obj==23.01 or obj==c or obj==f:
                 pass
             elif obj==k or obj=={}:
                 pass


test()


-- 
Bartc