如何在matplotlib.pyplot第二个子图添加水平线并保持颜色同步？

Hey there! Let's tackle your problem step by step—you want to add a horizontal line at y=100.000 to your second subplot, while keeping both subplots (and the line) using the same color. Here are two straightforward approaches:

Approach 1: Inherit the color from your first plot #

This method automatically picks up the color of your first curve, so you don't have to hardcode any color values:

import matplotlib.pyplot as plt

# Replace these with your actual data
px = [1, 2, 3, 4, 5]
py = [10, 20, 15, 25, 30]
curve = [50, 75, 90, 100, 120, 110]

# First subplot: plot and capture the line's color
plt.subplot(2, 1, 1)
# The comma extracts the single Line2D object from the returned list
line1, = plt.plot(px, py)
plot_color = line1.get_color()  # Get the color of the first line

# Second subplot: use the same color for the curve and horizontal line
plt.subplot(2, 1, 2)
plt.plot(curve, color=plot_color)
# Add the horizontal line at y=100.000, matching the plot color
plt.axhline(y=100.000, color=plot_color, linestyle='--', label='100.000')

# Optional: Add a legend to highlight the horizontal line
plt.legend()

# Adjust spacing to prevent overlapping labels
plt.tight_layout()
plt.show()

Approach 2: Manually specify a unified color #

If you prefer to control the exact color, just define a color value upfront and use it for all elements:

import matplotlib.pyplot as plt

# Define your desired color (use any valid matplotlib color: hex, name, RGB tuple)
plot_color = '#1f77b4'  # Matplotlib's default blue

# Your data (replace with real values)
px = [1, 2, 3, 4, 5]
py = [10, 20, 15, 25, 30]
curve = [50, 75, 90, 100, 120, 110]

plt.subplot(2, 1, 1)
plt.plot(px, py, color=plot_color)

plt.subplot(2, 1, 2)
plt.plot(curve, color=plot_color)
# Add horizontal line with the same color
plt.axhline(y=100.000, color=plot_color, linestyle='--')

plt.tight_layout()
plt.show()

Key Notes: #

• The plt.axhline() function is perfect for horizontal lines—it spans the entire width of the subplot by default.
• Use linestyle (like '--' for dashed, ':' for dotted) to distinguish the horizontal line from your main curve if needed.
• plt.tight_layout() ensures your subplots and labels don't overlap, making the figure cleaner.

内容的提问来源于stack exchange，提问作者Mike