Incorrect y-axis values when SI prefix is disabled

[matenestor]

Short description

I am plotting some data with values <1e-8 and customizing the plot axes and labels. When I disable SI prefix just before plotting the data (after other things are set, like axes labels and ranges), then the values on the y-axis are incorrect. The scientific notation suffix e-9 or e-10 is not shown.

Code to reproduce

import pyqtgraph as pg

arr = [
    1.20e-09, 1.66e-09, 1.99e-09, 2.10e-09, 1.96e-09,
    1.53e-09, 1.04e-09, 5.70e-10, 2.28e-10, 1.00e-10,
    2.17e-10, 6.35e-10, 1.12e-09, 1.59e-09, 1.95e-09,
    2.10e-09, 2.00e-09, 1.60e-09, 1.12e-09, 6.42e-10,
]

plot = pg.plot([0], [0])

plot.setLabel("bottom", "m/z")
plot.setLabel("left", "I[A]")

# correct
# plot.plotItem.getAxis("left").enableAutoSIPrefix(False)

plot.plotItem.setYRange(min=1e-11, max=25e-10)

# incorrect
plot.plotItem.getAxis("left").enableAutoSIPrefix(False)

plot.plot(x=list(range(len(arr))), y=arr)

# incorrect
# plot.plotItem.getAxis("left").enableAutoSIPrefix(False)

pg.exec()

Expected behavior

The data is plotted with correct value on the y-axis no matter in which order I call set methods on a plot instance.

Real behavior

1. When data is plotted before the SI prefix is disabled, then the data appear wrong.
2. When data is plotted after the SI prefix is disabled, then it works as intended, but
3. When a YRange is set before the SI prefix is disabled, then the data appear wrong again.

Tested environment(s)

• PyQtGraph version: 0.13.3
• Qt Python binding: PySide6 6.5.1.1

[sldesnoo-Delft]

The bug is in AxisItem.updateAutoSIPrefix and enableAutoSIPrefix. updateAutoSIPrefix doesn't check whether the attribute autoSIPrefix is True.
Calling enableAutoSIPrefix(False) after label and range are set still sets the value for autoSIPrefixScale. The method generateDrawSpecs doesn't check value of autoSIPrefix and always uses autoSIPrefixScale.

Proposed solution: set autoSIPrefixScale to 1.0 when autoSIPrefix == False.