Re: Quick question about CPython interpreter
On Tue, 18 Oct 2022 at 03:51, Stefan Ram wrote: > > MRAB writes: > >It can't optimise that because, say, 'print' could've been bound to a > >function that rebinds 'str'. > > It would be possible to find out whether a call of a function > named "print" is to the standard function, but the overhead > to do this in the end might slow down the execution. > > In general, it can be possible that there could be optimizer > stages after compilation. So, one might write a small micro- > benchmark to be sure. > You'd also have to ensure that the stringification of the ID doesn't change (which it can it it isn't a core data type), and the easiest way to do THAT is to call str() on the ID every time and see if it's the same... ChrisA -- https://mail.python.org/mailman/listinfo/python-list
Re: Quick question about CPython interpreter
On 2022-10-17 16:43, David Lowry-Duda wrote:
One can use the `dis` module and investigate the generated python
bytecode. For me, I get
# file "dis1.py"
thing = 123
for i in range(10):
if "hi" == str(thing):
print("found")
break
The bytecode is then
1 0 LOAD_CONST 0 (123)
2 STORE_NAME 0 (thing)
2 4 LOAD_NAME1 (range)
6 LOAD_CONST 1 (10)
8 CALL_FUNCTION1
10 GET_ITER
>> 12 FOR_ITER28 (to 42)
14 STORE_NAME 2 (i)
3 16 LOAD_CONST 2 ('hi')
18 LOAD_NAME3 (str)
20 LOAD_NAME0 (thing)
22 CALL_FUNCTION1
24 COMPARE_OP 2 (==)
26 POP_JUMP_IF_FALSE 12
4 28 LOAD_NAME4 (print)
30 LOAD_CONST 3 ('found')
32 CALL_FUNCTION1
34 POP_TOP
5 36 POP_TOP
38 JUMP_ABSOLUTE 42
40 JUMP_ABSOLUTE 12
>> 42 LOAD_CONST 4 (None)
44 RETURN_VALUE
I note that line 22 calls the function str repeatedly, and no
optimization is done here.
# file "dis2.py"
thing = 123
strthing = str(thing)
for i in range(10):
if "hi" == strthing:
print("found")
break
This generates bytecode
1 0 LOAD_CONST 0 (123)
2 STORE_NAME 0 (thing)
2 4 LOAD_NAME1 (str)
6 LOAD_NAME0 (thing)
8 CALL_FUNCTION1
10 STORE_NAME 2 (strthing)
3 12 LOAD_NAME3 (range)
14 LOAD_CONST 1 (10)
16 CALL_FUNCTION1
18 GET_ITER
>> 20 FOR_ITER24 (to 46)
22 STORE_NAME 4 (i)
4 24 LOAD_CONST 2 ('hi')
26 LOAD_NAME2 (strthing)
28 COMPARE_OP 2 (==)
30 POP_JUMP_IF_FALSE 20
5 32 LOAD_NAME5 (print)
34 LOAD_CONST 3 ('found')
36 CALL_FUNCTION1
38 POP_TOP
6 40 POP_TOP
42 JUMP_ABSOLUTE 46
44 JUMP_ABSOLUTE 20
>> 46 LOAD_CONST 4 (None)
48 RETURN_VALUE
In short, it seems the cpython interpreter doesn't (currently) perform
this sort of optimization.
It can't optimise that because, say, 'print' could've been bound to a
function that rebinds 'str'.
--
https://mail.python.org/mailman/listinfo/python-list
Re: Quick question about CPython interpreter
One can use the `dis` module and investigate the generated python
bytecode. For me, I get
# file "dis1.py"
thing = 123
for i in range(10):
if "hi" == str(thing):
print("found")
break
The bytecode is then
1 0 LOAD_CONST 0 (123)
2 STORE_NAME 0 (thing)
2 4 LOAD_NAME1 (range)
6 LOAD_CONST 1 (10)
8 CALL_FUNCTION1
10 GET_ITER
>> 12 FOR_ITER28 (to 42)
14 STORE_NAME 2 (i)
3 16 LOAD_CONST 2 ('hi')
18 LOAD_NAME3 (str)
20 LOAD_NAME0 (thing)
22 CALL_FUNCTION1
24 COMPARE_OP 2 (==)
26 POP_JUMP_IF_FALSE 12
4 28 LOAD_NAME4 (print)
30 LOAD_CONST 3 ('found')
32 CALL_FUNCTION1
34 POP_TOP
5 36 POP_TOP
38 JUMP_ABSOLUTE 42
40 JUMP_ABSOLUTE 12
>> 42 LOAD_CONST 4 (None)
44 RETURN_VALUE
I note that line 22 calls the function str repeatedly, and no
optimization is done here.
# file "dis2.py"
thing = 123
strthing = str(thing)
for i in range(10):
if "hi" == strthing:
print("found")
break
This generates bytecode
1 0 LOAD_CONST 0 (123)
2 STORE_NAME 0 (thing)
2 4 LOAD_NAME1 (str)
6 LOAD_NAME0 (thing)
8 CALL_FUNCTION1
10 STORE_NAME 2 (strthing)
3 12 LOAD_NAME3 (range)
14 LOAD_CONST 1 (10)
16 CALL_FUNCTION1
18 GET_ITER
>> 20 FOR_ITER24 (to 46)
22 STORE_NAME 4 (i)
4 24 LOAD_CONST 2 ('hi')
26 LOAD_NAME2 (strthing)
28 COMPARE_OP 2 (==)
30 POP_JUMP_IF_FALSE 20
5 32 LOAD_NAME5 (print)
34 LOAD_CONST 3 ('found')
36 CALL_FUNCTION1
38 POP_TOP
6 40 POP_TOP
42 JUMP_ABSOLUTE 46
44 JUMP_ABSOLUTE 20
>> 46 LOAD_CONST 4 (None)
48 RETURN_VALUE
In short, it seems the cpython interpreter doesn't (currently) perform
this sort of optimization.
- DLD
--
https://mail.python.org/mailman/listinfo/python-list
Re: Quick question about CPython interpreter
On 10/14/22 16:25, DFS wrote: > - > this does a str() conversion in the loop > - > for i in range(cells.count()): >if text == str(ID): > break > > > - > this does one str() conversion before the loop > - > strID = str(ID) > for i in range(cells.count()): >if text == strID: > break > > > But does CPython interpret the str() conversion away and essentially do > it for me in the first example? No. You can use the dis module to show you what CPython is doing under the hood. -- https://mail.python.org/mailman/listinfo/python-list
Quick question about CPython interpreter
- this does a str() conversion in the loop - for i in range(cells.count()): if text == str(ID): break - this does one str() conversion before the loop - strID = str(ID) for i in range(cells.count()): if text == strID: break But does CPython interpret the str() conversion away and essentially do it for me in the first example? -- https://mail.python.org/mailman/listinfo/python-list
