PyQtGraph errors in Spyder/IPython — Fixing common PyQtGraph color, font size, and compatibility issues

2020-05-07T09:00:00+00:00

I'm following a PyQtGraph tutorial and getting errors when I try to set colors and font sizes on my plot titles and labels. Using color names like 'blue' causes a ValueError, and passing size=30 as an integer gives a TypeError. What's going wrong and how do I fix it?

If you're working through PyQtGraph tutorials and running into errors when setting colors, titles, or font sizes, you're not alone. These issues come up frequently, especially when using older versions of PyQtGraph in environments like Spyder or IPython. The good news is that most of these problems have straightforward fixes.

In this article, we'll walk through the most common PyQtGraph errors related to colors and label formatting, explain why they happen, and show you how to solve them.

The color name error

You might see this error when trying to set a title color using a full color name like 'blue':

python

self.graphWidget.setTitle("Your Title Here", color='blue', size='30pt')

python

File "...\pyqtgraph\functions.py", line 182, in mkColor
    g = int(c[1]*2, 16)
ValueError: invalid literal for int() with base 16: 'll'

Or, when using 'black':

python

UnboundLocalError: local variable 'r' referenced before assignment

These errors occur because older versions of PyQtGraph's mkColor function don't understand full color names like 'blue' or 'black'. When you pass 'blue', PyQtGraph tries to interpret it as a hex color string, picks out individual characters ('l', 'u', etc.), and fails to parse them as hexadecimal values.

The fix: use single-letter color codes or update PyQtGraph

The simplest immediate fix is to use PyQtGraph's single-letter color codes instead of full color names:

Letter	Color
`'r'`	Red
`'g'`	Green
`'b'`	Blue
`'c'`	Cyan
`'m'`	Magenta
`'y'`	Yellow
`'k'`	Black
`'w'`	White

So instead of color='blue', use color='b':

python

self.graphWidget.setTitle("Your Title Here", color="b", size="30pt")

You can also pass colors as hex strings or RGB tuples:

python

# Hex color
self.graphWidget.setTitle("Your Title Here", color="#0000FF", size="30pt")

# RGB tuple (values 0-255)
self.graphWidget.setTitle("Your Title Here", color=(0, 0, 255), size="30pt")

The better long-term fix is to update PyQtGraph to a newer version, where full color name support has been improved:

pip install pyqtgraph --upgrade

The font size TypeError

Another common error appears when passing the size parameter as an integer:

python

self.graphWidget.setTitle("Your Title Here", color="b", size=30)

python

File "...\pyqtgraph\graphicsItems\LabelItem.py", line 61, in setText
    optlist.append('font-size: ' + opts['size'])
TypeError: can only concatenate str (not "int") to str

This happens because PyQtGraph's LabelItem.setText method builds a CSS style string internally. It expects the size value to already be a string with a unit suffix like '30pt'. When you pass the integer 30, Python can't concatenate a string and an integer.

The fix: pass size as a string with units

Always pass the size parameter as a string that includes the CSS unit:

python

self.graphWidget.setTitle("Your Title Here", color="b", size="30pt")

The pt suffix stands for "points," which is a standard CSS font-size unit. You could also use px (pixels) if you prefer:

python

self.graphWidget.setTitle("Your Title Here", color="b", size="30px")

Updating PyQtGraph

Many of these issues were fixed in later releases of PyQtGraph. If you're using an older version (especially anything before 0.11), upgrading will resolve most of these problems and give you access to better features and performance.

Check your current version:

pip show pyqtgraph

Upgrade to the latest version:

pip install pyqtgraph --upgrade

If you're using Anaconda (common with Spyder), you can also update through conda:

conda install -c conda-forge pyqtgraph

The `time.clock` error

If you're on Python 3.8 or later with an older PyQtGraph version, you may also see an error related to time.clock. This function was removed in Python 3.8. Upgrading PyQtGraph to version 0.11.0 or later fixes this as well.

A complete working example

Here's a complete example that uses the correct color and size formats, and should work across PyQtGraph versions:

python

import sys

from PyQt5.QtWidgets import QApplication, QMainWindow

import pyqtgraph as pg


class MainWindow(QMainWindow):
    def __init__(self):
        super().__init__()

        self.graphWidget = pg.PlotWidget()
        self.setCentralWidget(self.graphWidget)

        # Set background color
        self.graphWidget.setBackground("w")

        # Set title with single-letter color code and string size
        self.graphWidget.setTitle(
            "Temperature Over Time", color="b", size="20pt"
        )

        # Set axis labels
        styles = {"color": "r", "font-size": "18px"}
        self.graphWidget.setLabel("left", "Temperature (°C)", **styles)
        self.graphWidget.setLabel("bottom", "Time (min)", **styles)

        # Add grid
        self.graphWidget.showGrid(x=True, y=True)

        # Sample data
        hour = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
        temperature = [30, 32, 34, 32, 33, 31, 29, 32, 35, 30]

        # Plot with a blue pen
        pen = pg.mkPen(color="b", width=2)
        self.graphWidget.plot(hour, temperature, pen=pen)


app = QApplication(sys.argv)
window = MainWindow()
window.show()
sys.exit(app.exec_())

This example avoids all the common pitfalls:

Colors use single-letter codes ("b", "r") instead of full names
The title size is a string with a unit ("20pt")
Axis label styles use string values with units ("18px")

If you run this and see your plot with a blue title, red axis labels, and a line chart, everything is working correctly.

For an in-depth guide to building Python GUIs with PyQt5 see my book, Create GUI Applications with Python & Qt5.

Python GUIs - ipython

PyQtGraph errors in Spyder/IPython — Fixing common PyQtGraph color, font size, and compatibility issues

The color name error

The fix: use single-letter color codes or update PyQtGraph

The font size TypeError

The fix: pass size as a string with units

Updating PyQtGraph

The time.clock error

A complete working example

The `time.clock` error