[Python-Dev] Cannot declare the largest integer literal. (original) (raw)

Christian Tismer tismer@tismer.com
Mon, 08 May 2000 23:52:54 +0200

Tim Peters wrote:

[Tim] > Python's grammar is such that negative integer literals don't > exist; what you actually have there is the unary minus operator > applied to positive integer literals; ... [Christian Tismer] > Well, knowing that there are more negatives than positives > and then coding it this way appears in fact as a design flaw to me. Don't know what you're saying here.

On a 2's-complement machine, there are 2**(n-1) negatives, zero, and 2**(n-1)-1 positives. The most negative number cannot be inverted. Most machines today use the 2's complement.

Python's grammar has nothing to do with the relative number of positive vs negative entities; indeed, in a 2's-complement machine it's not even true that there are more negatives than positives.

If I read this 1's-complement machine then I believe it. But we don't need to split hair on known stuff :-)

Python generates the unary minus for "negative literals" because, again, negative literals don't exist in the grammar.

Yes. If I know the facts and don't build negative literals into the grammar, then I call it an oversight. Not too bad but not nice.

> A simple solution could be to do the opposite: > Always store a negative number and negate it > for positive numbers. ...

So long as negative literals don't exist in the grammar, "-2147483648" makes no sense on a 2's-complement machine with 32-bit C longs. There isn't "a problem" here worth fixing, although if there is , it will get fixed by magic as soon as Python ints and longs are unified.

I'd change the grammar.

ciao - chris

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