[PYTHON] List comprehensions are no longer slow in PyPy 7.3.1

List comprehensions are no longer slow in PyPy 7.3.1

I've almost finished what I want to say in the title ...

[Python Competitive Programming Acceleration Tips (Personally Be careful when doing Atcoder in Python)](https://juppy.hatenablog.com/entry/2019/06/14/Python_%E7%AB% B6% E6% 8A% 80% E3% 83% 97% E3% 83% AD% E3% 82% B0% E3% 83% A9% E3% 83% 9F% E3% 83% B3% E3% 82% B0% E9% AB% 98% E9% 80% 9F% E5% 8C% 96tips_% 28 Python% E3% 81% A7Atcoder% E3% 82% 92% E3% 82% 84% E3% 82% 8B% E9% 9A% 9B% E3% 81% AB% E5% 80% 8B # Pypy% E3% 81% 98% E3% 82% 83% E3% 81% A0% E3% 82% 81% E3% 81% AA% E3% 82% 82% As mentioned in E3% 81% AE), there was the fact that PyPy's list comprehensions were slow.

By the way, [https://morepypy.blogspot.com/2020/04/pypy-731-released.html](PyPy 7.3.1 released) has the following sentence.

improved JIT code generation for generators (and generator expressions in particular) when passing them to functions like sum, map, and map that consume them.

List comprehension is just like passing a generator expression to the list function !?

$ cat 1.py
n = 10**7

a = [0]*n
for i in range(n):
    a[i] = i*2

$ cat 2.py
n = 10**7

a = [i*2 for i in range(n)]

$ ./pypy3 --version
Python 3.6.9 (2ad108f17bdb, Apr 07 2020, 03:05:35)
[PyPy 7.3.1 with MSC v.1912 32 bit]

$ time ./pypy3.exe 1.py

real    0m0.149s
user    0m0.000s
sys     0m0.000s

$ time ./pypy3.exe 2.py

real    0m0.136s
user    0m0.015s
sys     0m0.000s

List comprehension is faster !!

$ ./pypy3 --version
Python 3.6.9 (1608da62bfc7, Dec 23 2019, 12:38:24)
[PyPy 7.3.0 with MSC v.1911 32 bit]

$ time ./pypy3.exe 1.py

real    0m0.146s
user    0m0.000s
sys     0m0.015s

$ time ./pypy3.exe 2.py

real    0m0.440s
user    0m0.000s
sys     0m0.015s

List comprehensions are about three times slower in PyPy 7.3.0.

Unfortunately, the language update for AtCoder is PyPy 7.3.0, isn't it? Sadness doesn't stop.

Postscript: It is alive and well that the addition of strings is hopelessly slow.

$ cat 3.py
n = 10**5
res = 'a'
for _ in [0]*n:
    res += 'a'

$ time ./pypy3 3.py

real    0m1.476s
user    0m0.000s
sys     0m0.015s

$ time python3 3.py

real    0m0.082s
user    0m0.015s
sys     0m0.062s