A fast, powerful, and extensible dice engine for D&D, d20 systems, and any other system that needs dice!
- Quick to start - just use
dice_parser.roll()
! - Optimised for speed and memory efficiency
- Highly extensible API for custom behaviour and dice stringification
- Built-in execution limits against malicious dice expressions
- Tree-based dice representation for easy traversal
Requires Python 3.10+.
python3 -m pip install git+https://github.com/lmaotrigine/dice-parser@main
>>> import dice_parser as dice
>>> result = dice.roll('1d20+5')
>>> str(result)
'1d20 (10) + 5 = `15`'
>>> result.total
15
>>> result.crit
<CritType.NORMAL: 0>
>>> str(result.ast)
'1d20 + 5'
This is the grammar supported by the dice parser, roughly ordered by how rightly the grammar binds.
These are the atoms used at the base of the syntax tree.
Name | Syntax | Description | Examples |
---|---|---|---|
literal | INT , DECIMAL |
A literal number. | 1 , 0.5 , 3.14 |
dice | INT? "d" (INT | "%") |
A set of die. | d20 , 3d6 |
set | "(" (num ("," num)* ","?)? ")" |
A set of expressions. | () , (2,) , (1, 3+3, 1d20) |
Note that (3d6)
is equivalent to 3d6
, but (3d6,)
is the set containing a single element 3d6
.
These operations can be performed on dice and sets.
Name | Syntax | Description | Examples |
---|---|---|---|
set_op | operation selector |
An operation on a set (see below). | kh3 , ro<3 |
selector | seltype INT |
A selection on a set (see below). | 3 , h1 , >2 |
Operators are always followed by a selector, and operate on the items in the set that match the selector.
Syntax | Name | Description |
---|---|---|
k | keep | Keeps all matched values. |
p | drop | Drops all matched values. |
rr | reroll | Rerolls all matched values until none match. (Dice only) |
ro | reroll once | Rerolls all matched values once. (Dice only) |
ra | reroll and add | Rerolls up to one matched value once, keeping the original roll. (Dice only) |
e | explode on | Rolls another die for each matched value. (Dice only) |
mi | minimum | Sets the minimum value of each die. (Dice only) |
ma | maximum | Sets the maximum value of each die. (Dice only) |
Selectors select from the remaining kept values in a set.
Syntax | Name | Description |
---|---|---|
X | literal | All values in this set that are literally this value. |
hX | highest X | The highest X values in the set. |
lX | lowest X | The lowest X values in the set. |
>X | greater than X | All values in this set greater than X. |
<X | less than X | All values in this set less than X. |
Syntax | Name | Description |
---|---|---|
+X | positive | Does nothing. |
-X | negative | The negative value of X. |
Syntax | Name |
---|---|
X * Y | multiplication |
X / Y | division |
X // Y | int division |
X % Y | modulo |
X + Y | addition |
X - Y | subtraction |
X == Y | equality |
X >= Y | greater/equal |
X <= Y | less/equal |
X > Y | greater than |
X < Y | less than |
X != Y | inequality |
>>> from dice_parser import roll
>>> r = roll('4d6kh3') # highest 3 of four 6-sided dice
>>> r.total
14
>>> str(r)
'4d6kh3 (4, 4, **6**, ~~3~~) = `14`'
>>> r = roll('2d6ro<3') # roll 2d6, then reroll any 1s or 2s once
>>> r.total
9
>>> str(r)
'2d6ro<3 (**~~1~~**, 3, **6**) = `9`'
>>> r = roll('8d6mi2') # roll 8d6, with each die having a minimum roll of 2
>>> r.total
33
>>> str(r)
'8d6mi2 (1 -> 2, **6**, 4, 2, **6**, 2, 5, **6**) = `33`'
>>> r = roll('(1d4 + 1, 3, 2d6kl1)kh1') # the highest of 1d4+1, 3, and the lower of 2d6
>>> r.total
3
>>> str(r)
'(1d4 (2) + 1, ~~3~~, ~~2d6kl1 (2, 5)~~)kh1 = `3`'
The default stringifier formats the result of each roll in Markdown, which may not be useful in your application.
To change this behaviour, you can create a subclass of dice_parser.Stringifier
(or dice_parser.SimpleStringifier
as a starting point), and implement the str_*
methods to customize how your dice
tree is stringified
Then, simply pass an instance of your stringifier into the roll()
function!
>>> import dice_parser
>>> class MyStringifier(dice_parser.SimpleStringifier):
... def stringify_node(self, node):
... if not node.kept:
... return 'X'
... return super().stringify_node(node)
...
... def str_expression(self, node):
... return f'The result of the roll {self.stringify_node(node.roll)} was {int(node.total)}'
...
>>> result = dice_parser.roll('4d6e6kh3', stringifier=MyStringifier())
>>> str(result)
'The result of the roll 4d6e6kh3 (X, 5, 6!, 6!, X, X) was 17'
Each dice node supports value annotations - i.e., a method to "tag" parts of a roll with some indicator. For example,
>>> from dice_parser import roll
>>> str(roll('3d6 [fire] + 1d4 [piercing]'))
'3d6 (3, 2, 2) [fire] + 1d4 (3) [piercing] = `10`'
>>> str(roll('-(1d8 + 3) [healing]'))
'-(1d8 (7) + 3) [healing] = `-10`'
>>> str(roll('(1 [one], 2 [two] 3 [three])'))
'(1 [one], 2 [two], 3 [three]) = `6`'
are all examples of valid annotations. Annotations are purely visual and do not affect the evaluation of the roll by default.
Additionally, when allow_comments=True
is passed to roll()
, the result of the roll may have a comment:
>>> from dice_parser import roll
>>> result = roll('1d20 I rolled a d20', allow_comments=True)
>>> str(result)
'1d20 (13) = `13`'
>>> result.comment
'I rolled a d20'
Note that while allow_comments
is enabled, AST caching is disabled, which may lead to slightly worse performance.
By default, the parser caches the 256 most frequently used dice expressions in an LFU cache, allowing for a significant
speedup when rolling many of the same kinds of rolls. This caching is disabled when allow_comments
is True.
With caching:
$ python -m timeit -s "from dice_parser import roll" "roll('1d20')"
10000 loops, best of 5: 21.6 usec per loop
$ python -m timeit -s "from dice_parser import roll" "roll('100d20')"
500 loops, best of 5: 572 usec per loop
$ python3 -m timeit -s "from dice_parser import roll; expr='1d20+'*50+'1d20'" "roll(expr)"
500 loops, best of 5: 732 usec per loop
$ python3 -m timeit -s "from dice_parser import roll" "roll('10d20rr<20')"
1000 loops, best of 5: 1.13 msec per loop
Without caching:
$ python3 -m timeit -s "from dice_parser import roll" "roll('1d20')"
5000 loops, best of 5: 61.6 usec per loop
$ python3 -m timeit -s "from dice_parser import roll" "roll('100d20')"
500 loops, best of 5: 620 usec per loop
$ python3 -m timeit -s "from dice_parser import roll; expr='1d20+'*50+'1d20'" "roll(expr)"
500 loops, best of 5: 2.1 msec per loop
$ python3 -m timeit -s "from dice_parser import roll" "roll('10d20rr<20')"
1000 loops, best of 5: 1.26 msec per loop