Quickstart: Python

eunoia is the Python binding. You hand euler() a dict of set sizes, it fits an area-proportional diagram, and .plot() renders it with matplotlib.

Install

pip install eunoia

Wheels ship for all common platforms, so no Rust toolchain is needed. Plotting uses matplotlib (a dependency).

Fit a diagram

import eunoia as eu
import matplotlib.pyplot as plt

fit = eu.euler({"A": 5, "B": 3, "A&B": 1.5})
print(fit)  # residual table + goodness-of-fit metrics
fit.plot()
plt.show()

The input dict is keyed by combination expression: a single set ("A") or sets joined with & ("A&B"). Values are exclusive by default: the part of A outside B is 5, the overlap is 1.5. Pass input="inclusive" if your numbers are full set sizes and the core will decompose them:

fit = eu.euler({"A": 8, "B": 4.5, "A&B": 1.5}, input="inclusive")

The result carries the fitted geometry and fit statistics:

fit.shapes        # list of fitted Circle/Ellipse structs
fit.loss          # objective value (lower is better)
fit.diag_error    # largest single-region error

Pick a different shape

fit = eu.euler({"A": 5, "B": 3, "A&B": 1.5}, shape="ellipse")
fit.plot(quantities=True)

shape is one of "circle" (default), "ellipse", "square", or "rectangle". Ellipses are more flexible and often fit three or more sets noticeably better; see Shapes.

Customize the plot

fit.plot(
    colors=["#e41a1c", "#377eb8"],  # per-set
    quantities="fitted",            # show fitted areas at region anchors
    labels=True,
    edges={"linewidth": 1.5},
)

eunoia.options(...) sets defaults for every subsequent plot; reset_options() reverts to the built-ins.

Venn diagrams

For a fixed, non-proportional Venn template (every intersection shown regardless of size), use venn(); it accepts a set count, a list of names, or a mapping:

fit = eu.venn(["A", "B", "C"])
fit.plot(quantities=True)

Ellipse Venn diagrams support 1–5 sets; circle, square, and rectangle support 1–3.

Next steps

The full API reference lives on the eunoia-py docs site. For how the fit works across all bindings, see the Fitter pipeline and Goodness of fit chapters.