python mmap to concatenate csv files

csv.py

❯ rm out.csv
❯ cat 1.py
from glob import glob
import mmap

files = glob("data/*")

files.sort(key=lambda x: int(x.split("/")[-1].split(".")[0]))
write_f = open("out.csv", "w+b")

for i, fname in enumerate(files):
    with open(fname, "r+b") as f:
        with mmap.mmap(f.fileno(), 0) as mm:
            if i == 0:
                write_f.write(mm.readline())
            else:
                mm.readline()
            write_f.write(mm.read())

write_f.close()
❯ time python 1.py
python 1.py  0.90s user 1.12s system 99% cpu 2.022 total
❯ wc -l out.csv
10000001 out.csv