On 16/09/21 4:23 am, Mostowski Collapse wrote:
I really wonder why my Python implementation
is a factor 40 slower than my JavaScript implementation.
There are Javascript implementations around nowadays that are
blazingly fast. Partly that's because a lot of effort has been
put into them, but it's also because Javascript is a different
language. There are many dynamic aspects to Python that make
fast implementations difficult.
I use in Python:
temp = [NotImplemented] * code[pos]
pos += 1
is the the idiom [_] * _ slow?
No, on the contrary it's probably the fastest way to do it
in Python. You could improve it a bit by precomputing
[NotImplemented]:
# once at the module level
NotImplementedList = [NotImplemented]
# whenever you want a new list
temp = NotImplementedList * code[pos]
That's probably at least as fast as built-in function for
creating lists would be.
does it really first create an
array of size 1 and then enlarge it?
It does:
>>> def f(code, pos):
... return [NotImplemented] * code[pos]
...
>>> from dis import dis
>>> dis(f)
2 0 LOAD_GLOBAL 0 (NotImplemented)
2 BUILD_LIST 1
4 LOAD_FAST 0 (code)
6 LOAD_FAST 1 (pos)
8 BINARY_SUBSCR
10 BINARY_MULTIPLY
12 RETURN_VALUE
BTW, the Python terminology is "list", not "array".
(There *is* something in the stdlib called an array, but
it's rarely used or needed.)
--
Greg
--
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