Great question! The default behavior for Matplotlib's axis offset text (like the 1e-6 in your plot) is to sit at the top of the Y-axis. While ax.yaxis.set_offset_position('left') or ('right') shifts it to the left/right side of that top position, it doesn't place it along the side of the axis (aligned with tick labels, for example).

Here are a few practical ways to fix this:

Option 1: Manually Reposition the Offset Text #

You can directly grab the offset text object and adjust its position using axis coordinates, so it sits vertically centered alongside the Y-axis ticks:

import matplotlib.pyplot as plt

fig, ax = plt.subplots()
ax.plot([0,1],[0,1e-6],'o-')

# Get the offset text object from the Y-axis
offset_text = ax.yaxis.get_offset_text()

# Use axis coordinates (transAxes) to place it left of the Y-axis, vertically centered
# (0,0) = bottom-left of the axis area, (1,1) = top-right; negative x moves left outside the axis
offset_text.set_position((-0.1, 0.5))
offset_text.set_transform(ax.transAxes)

# Align the text so it sits neatly against the Y-axis
offset_text.set_ha('right')  # Horizontal right alignment
offset_text.set_va('center') # Vertical center alignment

ax.set_xlabel('$x$')
ax.set_ylabel('$y$')
plt.show()

Option 2: Integrate Offset Text into the Y-Axis Label #

If you prefer a cleaner look, you can hide the default offset text and append its value directly to your Y-axis label:

import matplotlib.pyplot as plt

fig, ax = plt.subplots()
ax.plot([0,1],[0,1e-6],'o-')

offset_text = ax.yaxis.get_offset_text()
# Grab the offset string and hide the original text
offset_str = offset_text.get_text()
offset_text.set_visible(False)

# Update the Y-label to include the offset
ax.set_ylabel(f'$y$ ({offset_str})')

ax.set_xlabel('$x$')
plt.show()

Option 3: Use Transformations for Dynamic Positioning #

For plots where the axis might resize, using a blended transform ensures the offset text stays aligned with the tick labels:

import matplotlib.pyplot as plt
import matplotlib.transforms as transforms

fig, ax = plt.subplots()
ax.plot([0,1],[0,1e-6],'o-')

offset_text = ax.yaxis.get_offset_text()
# Create a transform that aligns with the tick label horizontal position, and axis vertical position
tick_transform = ax.yaxis.get_ticklabels()[0].get_transform()
offset_transform = transforms.blended_transform_factory(
    tick_transform.transform_axes((0, 0)),  # Match tick label horizontal position
    ax.transAxes  # Use axis vertical coordinates
)

offset_text.set_transform(offset_transform)
offset_text.set_ha('right')
offset_text.set_va('center')

ax.set_xlabel('$x$')
ax.set_ylabel('$y$')
plt.show()

All these approaches let you move the offset text away from the top of the Y-axis and place it exactly where you want it on the side.

内容的提问来源于stack exchange，提问作者Hongcheng Ni