How to use ax.get_ylim() in matplotlib?

The ax.get_ylim() method in matplotlib returns the current y-axis limits as a tuple containing the minimum and maximum values. This is useful for understanding the current scale of your plot or for programmatically adjusting other plot elements based on the y-axis range.

Syntax

ax.get_ylim()

Return Value

Returns a tuple (ymin, ymax) representing the current y-axis limits.

Basic Example

Here's how to use ax.get_ylim() to retrieve the y-axis limits ?

import numpy as np
import matplotlib.pyplot as plt

# Set figure size
plt.rcParams["figure.figsize"] = [7.00, 3.50]
plt.rcParams["figure.autolayout"] = True

# Create figure and axis
fig, ax = plt.subplots()

# Create random data points
y = np.random.rand(10)

# Plot the data points
ax.plot(y, 'b-', marker='o')

# Get and print the y-axis limits
ylimits = ax.get_ylim()
print("Y-axis limits:", ylimits)
print(f"Minimum y-value: {ylimits[0]:.3f}")
print(f"Maximum y-value: {ylimits[1]:.3f}")

plt.title('Random Data Plot')
plt.show()

Y-axis limits: (-0.05, 1.05)
Minimum y-value: -0.050
Maximum y-value: 1.050

Practical Use Case

You can use get_ylim() to add annotations or elements relative to the current axis limits ?

import matplotlib.pyplot as plt
import numpy as np

# Create sample data
x = np.linspace(0, 10, 50)
y = np.sin(x) * np.exp(-x/10)

fig, ax = plt.subplots(figsize=(8, 4))
ax.plot(x, y, 'b-', linewidth=2)

# Get current y-limits
ymin, ymax = ax.get_ylim()

# Add a horizontal line at 80% of the y-range
threshold = ymin + 0.8 * (ymax - ymin)
ax.axhline(y=threshold, color='red', linestyle='--', alpha=0.7)

# Add text annotation using the limits
ax.text(5, threshold + 0.05, f'80% threshold: {threshold:.2f}', 
        ha='center', va='bottom', color='red')

print(f"Current y-limits: {ymin:.3f} to {ymax:.3f}")
print(f"Y-range span: {ymax - ymin:.3f}")

plt.title('Using get_ylim() for Annotations')
plt.grid(True, alpha=0.3)
plt.show()

Current y-limits: -0.105 to 1.050
Y-range span: 1.155

Comparison with set_ylim()

Conclusion

The ax.get_ylim() method is essential for retrieving current y-axis limits in matplotlib. Use it to understand your plot's scale or to programmatically position elements relative to the current axis range.