How about something like:

>>> def t1(*argv):
...     value = 0
...     for n in argv:
...         value *= 1_000
...         value += n
...     return value

>>> t1(123, 456, 789)

Similarly, for define t2 to use 1_000_000, t3 to use 1_000_000_000 and so on, instead of 1_000. For really big numbers, you might want to use t10.

I think something like
>>> t10(
...     111_222_333_444_555_666_777_888_999_000,
...     111_222_333_444_555_666_777_888_999_000,
...     111_222_333_444_555_666_777_888_999_000,
... )
gives a nice representation of a 90 digit number.

I think everyone on this thread thought this way once, but this way is a bother.
If you want to type a very long number, we may code like this in Jonathans proposal.

>>> t1(3, 826, 393, 629, 472, 794, 629, 263, 026, 302...

But if you noticed that you did typo in very last argument(=low digit), you need to remove and add commas.
This is really a burden.

In this respect, I'd agree with making new syntax.

Finally, perhaps really big numbers should be stored as data, rather than placed in source code files. (For example, this would allow these large pieces of data to be verified, via a secure hash.)

As your thought, I think big numbers like MBytes should be stored as data, but how about big constant or something like that?
I believe those kind of numbers should be stored in some python files like .

Yamato Nagata