A python script for "rolling" dice notation used in table-top RPGs and a script for modeling the results.
Many table-top role-playing games use the following notation to describe rolls that players make:
NdX
Where N is the number of dice and X is the number of sides on each die.
For example, damage from a rapier in D&D:
1d6+DEX piercing damage
or a quantity of treasure
3d6*100 copper pieces
rolldice is a program that interprets and emulates this notation, producing a quantity and identifier pair
modeldice is a program that interprets and models the notation, producing a probability distribution of the roll
Both programs accept a string argument formatted as a comma-separated list of things to roll and string IDs, such as "2d2 birds, 7d4 fish".
The 'd' in the dice notation is treated like an operator. It means "roll a die with [number after the d] sides [number before the d] times and sum the result."
It is interpreted as an operator after the parentheses: Parentheses, Dice, Exponents, Multiplication, Addition
It is important to note, though, that the order of operations on either side of the d is not assumed to be left-right.
"2d4d6" is arbitrary, and will throw an error.
"(2d4)d6" and "2d(4d6)" are both acceptable.
The expression can use most mathematics that python normally supports:
"(-2d4+(7d8)**2)d10/5+2d6%2"
In D&D 5e, Wizards of the Coast introduced an "advantage/disadvantage" system, which basically means you drop the lowest or the highest of 2d20. Long before that, the standard way to produce a new heroic character's attribute scores was to roll 4d6 and drop the lowest for each attribute.
In order to do that, use the l or h modifier to drop the lowest or highest:
NdX<[l|h][M]
where M is the number to drop from that end.
Advantage: "2d20l1"
Disadvantage: `"2d20h1"'
Stat roll: 4d6l1 STR, 4d6l1 DEX, 4d6l1 CON, 4d6l1 INT, 4d6l1 WIS, 4d6l1 CHA
It is important to know that the dice model is an exhaustive, brute force method that does not work well for large numbers. For example:
modeldice "4d6l1" takes very little time to complete.
modeldice "3d100" takes a very long time to complete.
This is a bug and needs a better solution.