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Speedup default PlotWidget/PlotItem initialization #3315

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Speedup default PlotWidget/PlotItem initialization #3315

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@Gatsik Gatsik commented May 29, 2025

I needed to generate a bunch of plots and noticed that it was quite slow. This PR tries to reduce the number of overheads on initializing PlotWidget by implementing several optimizations:

  • Don't initialize ViewBoxMenu on PlotWidget init. Create them on mouse events (or when one wants ot access menu property explicitly) instead when needed -- many setupUi() calls required to create menu are expensive
  • Remove WidgetGroup from ViewBoxMenu -- they were unused there -- reduces expensive autoAdd() method recursions
  • Create helper methods to set only necessary AxisItem properties and avoid calling _updateLabel during initialization (setHtml is quite expensive!)
  • Don't set LabelItem text during initialization if text is empty (since setHtml is slow)
  • Remove slot connections by name from AxisItem and PlotItem UI templates (unused) (to avoid generating these calls, pass -a option to uic)
  • Replace some double dict lookups with try..except blocks

Here are my benchmarks with this script:

import time

from PyQt6.QtWidgets import QApplication

import pyqtgraph as pg


def main() -> int:
    app = QApplication([])
    start = time.perf_counter()
    for _ in range(20):
        pg.PlotWidget()
    end = time.perf_counter()
    print(end - start)
    return 0


if __name__ == "__main__":
    raise SystemExit(main())
  • before: 0.5176408999977866
  • after: 0.28181239999685204

And also cProfile results (before and after respectively):
profile_before
profile_after

obtained by running this script:

import cProfile

from PyQt6.QtWidgets import QApplication

import pyqtgraph as pg


def main() -> int:
    app = QApplication([])
    with cProfile.Profile() as pr:
        for _ in range(20):
            pg.PlotWidget()
    pr.dump_stats("profile.pstat")
    return 0


if __name__ == "__main__":
    raise SystemExit(main())

and converting results to svg with yelp-gprof2dot and graphviz

github-advanced-security[bot]
github-advanced-security bot found potential problems May 29, 2025
View reviewed changes
pyqtgraph/graphicsItems/PlotItem/PlotItem.py
for label in self.axes:
try:
labels[label] = kwargs.pop(label)
except KeyError:

Check notice

Code scanning / CodeQL

Empty except Note

'except' clause does nothing but pass and there is no explanatory comment.
github-advanced-security[bot]
github-advanced-security bot found potential problems May 30, 2025
View reviewed changes
@Gatsik Gatsik force-pushed the plotwidget-init-speedup branch from 5522457 to d959deb Compare May 30, 2025 10:39
@Gatsik
Speedup PlotWidget initialization by removing some overhead
66d44ce 
Multiple PlotWidget initialization is quite slow

* Don't initialize ViewBoxMenu on PlotWidget init
  Create them on mouse events instead when needed --
  many `setupUi()` calls are expensive
* Remove WidgetGroup from ViewBoxMenu -- they weren't used
  anywhere -- reduces expensive `autoAdd()` method recursions
* Create helper methods to set only necessary AxisItem properties
  and avoid calling `_updateLabel` during initialization
  (`setHtml` is quite expensive!)
* Don't set LabelItem text during initialization if text is empty
  (since `setHtml` is slow)
* Remove slot connections by name from Axis and PlotItem UI
  templates (unused) (to avoid generating these calls, pass `-a`
  option to `uic`)
* Replace some dict lookups with `try..except` blocks
@Gatsik
Trim trailing whitespaces
5cf7bc0 
and sort imports
in files affected by commit
20a9acd
@Gatsik
Restore original behaviour of WidgetGroup.findWidget method
480967d
@Gatsik
Fix typehint and missing arg
51fb081
@Gatsik Gatsik force-pushed the plotwidget-init-speedup branch from f3fcbd6 to 51fb081 Compare November 17, 2025 22:36
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