prspace

Probability spaces with the same syntax in Python and R: Pr[X == 0] = 0.25.

Alpha. The API may change between 0.x releases.

import math
from prspace import PrSpace, Event

n_samples = math.comb(19, 10)
Pr = PrSpace()
S_B = Event(support="count")  # 0, 1, 2, ...

for B in (100, 1000):
    Pr[S_B == 0] = math.prod(1 - k / n_samples for k in range(B))
    print("Pr[S_B >= 1] =", Pr[S_B >= 1])  # derived: S_B is a count

print(Pr)
# PrSpace with 1 probability:
#   Pr[S_B == 0] = 0.004397413

• Complements are derived: after Pr[X == 0] = 0.25, Pr[X != 0] and Pr[~(X == 0)] are 0.75.
• Event(support=...) takes "real" (default), "integer", "count", or a list like [1, 2, 3] or ["H", "T"], and anything the rules of probability then pin down is derived.
• PrSpace(check="warn" | "error" | "off", derive=True): assignments that contradict earlier ones warn or raise InconsistentProbabilityError, saying which values would have been consistent.
• Reading a value that can't be determined raises UndefinedProbabilityError (a KeyError) with the known bounds in .lower and .upper.
• Event names are inferred from the variable they're bound to, or pass Event("name").

The R package has the same syntax. See the repository for both.