pyqt5-chart-widget 2.1.0

Lightweight interactive chart widget for PyQt5 with built-in approximation, multi-series, and extensible fit modes

pyqt5-chart-widget

A self-contained, dependency-free chart widget for PyQt5. No matplotlib, no pyqtgraph — drop the package into your project and go.

Built for an industrial powder feeder control application where the charting library needed to be small, fast, and not require a science degree to integrate.

Install

pip install pyqt5-chart-widget

Requires Python ≥ 3.8 and PyQt5 ≥ 5.15.

---

Quickstart

import sys
from PyQt5.QtWidgets import QApplication, QMainWindow
from pyqt5_chart_widget import ChartWidget

app = QApplication(sys.argv)
win = QMainWindow()

chart = ChartWidget()
chart.setLabel("left",   "Flow, g/min")
chart.setLabel("bottom", "RPM")

xs = [i * 100 for i in range(20)]
ys = [x * 0.05 + x ** 1.1 * 0.0003 for x in xs]

line = chart.plot(label="Pump A")
line.setData(xs=xs, ys=ys)

scatter = chart.addScatter(size=10, label="Calibration")
scatter.setData(x=xs[::3], y=ys[::3])

fit = chart.addFit(line, mode_key="poly3", label="Polynomial fit")

win.setCentralWidget(chart)
win.resize(900, 500)
win.show()
sys.exit(app.exec_())

---

API

ChartWidget

ChartWidget(
    parent=None,
    show_toolbar: bool = True,
    show_legend:  bool = False,
    show_sidebar: bool = False,
    font: QFont | None = None,
)

Method	Description
plot(color, width, label, dashed)	Add a line series → _LineItem
addScatter(size, color, label)	Add a scatter series → _ScatterItem
addFit(source, mode_key, color, width, dashed, label)	Add a fit curve for a series → _FitItem
addLine(y=, x=, color, width, dashed)	Add an infinite reference line → _InfLine
setLabel(side, text)	Set axis label — "left" or "bottom"
autofit()	Fit view to data bounds
setToolbarVisible(visible)	Show / hide the toolbar
setSidebarVisible(visible)	Show / hide the sidebar
setLegendVisible(visible)	Show / hide the legend overlay
sidebar()	Return the SidebarLabel instance (or None)
removeItem(item)	Remove any series or line
clearAll()	Remove all series
refreshFitMenu()	Rebuild the fit-mode dropdown (call after register_fit_mode)
exportCsv()	Open save dialog, write all series to CSV
exportImage()	Open save dialog, save canvas as PNG
grabImage()	Return QPixmap of the canvas without dialog

All color arguments accept any string QColor understands: "#e74c3c", "red", "rgb(200,100,50)".
If color is omitted, a color is chosen automatically from the palette.

---

Series items

line.setData(xs=[...], ys=[...])
line.setVisible(True)
line.setLabel("My series")

scatter.setData(x=[...], y=[...])

fit.setModeKey("spline")     # change fit algorithm live
fit.setVisible(False)

hline = chart.addLine(y=100.0, color="#f39c12", dashed=True)
hline.setValue(150.0)
hline.setVisible(True)

---

Built-in fit modes

Key	Description	Min points
linear_origin	Linear through origin (y = kx)	1
linear	Ordinary linear regression	2
poly2	Polynomial degree 2	2
poly3	Polynomial degree 3	2
poly4	Polynomial degree 4	2
pchip	Piecewise Cubic Hermite (monotone)	2
spline	Natural cubic spline	2

---

Custom fit modes

from pyqt5_chart_widget import FitMode, register_fit_mode

def my_fit(x_pts, y_pts, x_eval):
    # x_pts / y_pts are pre-sorted, de-duplicated
    # return a list of float values the same length as x_eval
    k = sum(xi * yi for xi, yi in zip(x_pts, y_pts)) / sum(xi**2 for xi in x_pts)
    return [k * xi for xi in x_eval]

register_fit_mode(FitMode("my_fit", "My custom fit", my_fit, min_points=2))

# Then rebuild the dropdown if the chart is already visible:
chart.refreshFitMenu()

---

Sidebar

chart = ChartWidget(show_sidebar=True)
sb = chart.sidebar()

sb.addLabel("Controls")
sb.addSeparator()
sb.addButton("Toggle line", lambda: line.setVisible(not line.visible))
sb.addButton("Export CSV",  chart.exportCsv, tooltip="Save data")
sb.clear()

---

Legend

chart = ChartWidget(show_legend=True)
# or toggle at runtime:
chart.setLegendVisible(True)

Series are shown in the legend only when they have a label and are visible.

---

Color palette

from pyqt5_chart_widget import set_palette, reset_colors

set_palette(["#ff0000", "#00ff00", "#0000ff"])  # replaces built-in palette
reset_colors()                                    # restart auto-color index

---

Internationalization

from pyqt5_chart_widget import set_tr, update_strings

# Option 1 — hook into your own tr() function
set_tr(lambda key: my_app_translations.get(key, key))

# Option 2 — patch individual strings
update_strings({
    "chart_widget.btn_fit":  "⊞ Autofit",
    "chart_widget.btn_csv":  "💾 CSV",
})

---

Interaction

Action	Result
Scroll wheel	Zoom in/out centered on cursor
Left drag	Pan
Double-click	Reset view to data bounds
Hover	Crosshair + snap to nearest point + tangent

---

Module layout

pyqt5_chart_widget/
├── __init__.py      # public API re-exports
├── chart_widget.py  # ChartWidget — main widget & toolbar
├── canvas.py        # _PlotCanvas — rendering engine
├── items.py         # _LineItem, _ScatterItem, _FitItem, _InfLine
├── math_utils.py    # FitMode, built-in fitters, register_fit_mode, nice_ticks
├── sidebar.py       # SidebarLabel — optional left panel
├── palette.py       # auto-color palette helpers
└── i18n.py          # tr(), set_tr(), update_strings()

---

Why not matplotlib / pyqtgraph?

Matplotlib embedded in Qt is slow to import, awkward to theme, and overkill for one calibration curve. Pyqtgraph is excellent but pulls in numpy as a hard dependency. This widget is ~900 lines total, has zero runtime dependencies beyond PyQt5, and does exactly what it says on the tin.

---

License

MIT