Making a number list in a .txt file

[gruntfutuk]

with open("dico.txt","w") as f:
    for a in range(999999):
        f.write('{0:0>6}\n'.format(a))

---

'{0:0>6}\n'
{
0 = first variable
:0 = fill
> = left adjust
6 = six spaces
}

---

left adjust not needed for zero padding

with open("dico.txt","w") as f:
    for a in range(999999):
        f.write('{0:06}\n'.format(a))

I'd intended to leave it to the OP to figure out how to do the padding without the function they originally coded.

Not sure the OP wants the \n between numbers either.

That said, why not f-strings rather than format?