Handling very large numbers in Python

Question

I ve been considering fast poker hand evaluation in Python  It occurred to me that one way to speed the process up would be to represent all the card faces and suits as prime numbers and multiply them together to represent the hands  To whit   class PokerCard      faces    23456789TJQKA      suits    cdhs      facePrimes    11  13  17  19  23  29  31  37  41  43  53  59  61      suitPrimes    2  3  5  7    AND      def HashVal self         return PokerCard facePrimes self cardFace    PokerCard suitPrimes self cardSuit    This would give each hand a numeric value that  through modulo could tell me how many kings are in the hand or how many hearts  For example  any hand with five or more clubs in it would divide evenly by 2 5  any hand with four kings would divide evenly by 59 4  etc   The problem is that a seven-card hand like AcAdAhAsKdKhKs has a hash value of approximately 62 7 quadrillion  which would take considerably more than 32 bits to represent internally  Is there a way to store such large numbers in Python that will allow me to perform arithmetic operations on it

User · Answer

The python interpreter will handle it for you, you just have to do your operations (+, -, *, /), and it will work as normal.

The int value is unlimited.

Careful when doing division, by default the quotient is turned into float, but float does not support such large numbers. If you get an error message saying float does not support such large numbers, then it means the quotient is too large to be stored in float you’ll have to use floor division (//).

It ignores any decimal that comes after the decimal point, this way, the result will be int, so you can have a large number result.

>>>10//3
3

>>>10//4
2

User · Answer

You could do this for the fun of it  but other than that it s not a good idea   It would not speed up anything I can think of    Getting the cards in a hand will be an integer factoring operation which is much more expensive than just accessing an array  Adding cards would be multiplication  and removing cards division  both of large multi-word numbers  which are more expensive operations than adding or removing elements from lists  The actual numeric value of a hand will tell you nothing   You will need to factor the primes and follow the Poker rules to compare two hands   h1  lt  h2 for such hands means nothing

User · Answer

Python supports a  bignum  integer type which can work with arbitrarily large numbers  In Python 2 5   this type is called long and is separate from the int type  but the interpreter will automatically use whichever is more appropriate  In Python 3 0   the int type has been dropped completely   That s just an implementation detail  though     as long as you have version 2 5 or better  just perform standard math operations and any number which exceeds the boundaries of 32-bit math will be automatically  and transparently  converted to a bignum   You can find all the gory details in PEP 0237

User · Answer

python supports arbitrarily large integers naturally   In  1   59  3 61  4 2 3 5 7 3 5 7 Out 1   62702371781194950 In  2       61  4 Out 2   0

User · Answer

python supports arbitrarily large integers naturally  example   gt  gt  gt  10  1000 10000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000  You could even get  for example of a huge integer value  fib 4000000   But still it does not  for now  supports an arbitrarily large float    If you need one big  large  float then check up on the decimal Module  There are examples of use on these foruns  OverflowError   34    39 Result too large  39   Another reference  http   docs python org 2 library decimal html You can even using the gmpy module if you need a speed-up  which is likely to be of your interest   Handling big numbers in code Another reference  https   code google com p gmpy

[python] Handling very large numbers in Python

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