Adding Text

Add text labels and descriptions directly to your plots.

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ax.text()

Add text at specific data coordinates:

import matplotlib.pyplot as plt

fig, ax = plt.subplots(figsize=(12, 3))

ax.grid(True)
ax.set_xlim(-0.5, 3.5)
ax.set_ylim(-0.05, 0.25)
ax.axhline(0, xmin=-0.5, xmax=3.5)

ax.text(0, 0.1, "Text label", fontsize=14, family="serif")
ax.text(2, 0.1, "Equation: $i\\hbar\\partial_t \\Psi = \\hat{H}\\Psi$", 
        fontsize=14, family="serif")

plt.show()

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Text Parameters

Common parameters for ax.text():

ax.text(
    x, y,                      # Position in data coordinates
    s,                         # Text string
    fontsize=12,               # Font size
    fontweight='bold',         # 'normal', 'bold', 'light', etc.
    fontstyle='italic',        # 'normal', 'italic', 'oblique'
    fontfamily='serif',        # 'serif', 'sans-serif', 'monospace'
    color='blue',              # Text color
    alpha=0.8,                 # Transparency
    rotation=45,               # Rotation angle
    ha='center',               # Horizontal alignment
    va='center',               # Vertical alignment
    backgroundcolor='yellow',  # Background color
    bbox=dict(...)             # Background box properties
)

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Text Alignment

Control horizontal alignment (ha) and vertical alignment (va):

import matplotlib.pyplot as plt

fig, ax = plt.subplots(figsize=(8, 6))
ax.set_xlim(0, 1)
ax.set_ylim(0, 1)

# Horizontal alignment options
ax.text(0.5, 0.8, "ha='left'", ha='left', fontsize=12)
ax.text(0.5, 0.6, "ha='center'", ha='center', fontsize=12)
ax.text(0.5, 0.4, "ha='right'", ha='right', fontsize=12)

# Mark the x=0.5 position
ax.axvline(0.5, color='gray', linestyle='--', alpha=0.5)

plt.show()

---

Text with Box

Add a box around text:

import matplotlib.pyplot as plt

fig, ax = plt.subplots()
ax.set_xlim(0, 1)
ax.set_ylim(0, 1)

# Simple box
ax.text(0.5, 0.7, "Text with box", 
        fontsize=14,
        bbox=dict(boxstyle='round', facecolor='wheat', alpha=0.5))

# Different box styles
ax.text(0.5, 0.5, "Square box", 
        fontsize=14,
        bbox=dict(boxstyle='square', facecolor='lightblue'))

ax.text(0.5, 0.3, "Round with padding", 
        fontsize=14,
        bbox=dict(boxstyle='round,pad=0.5', facecolor='lightgreen'))

plt.show()

Box styles: 'square', 'round', 'round4', 'circle', 'larrow', 'rarrow', 'darrow'

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Transform Coordinates

Use different coordinate systems:

import matplotlib.pyplot as plt

fig, ax = plt.subplots()
ax.plot([0, 1], [0, 1])

# Data coordinates (default)
ax.text(0.5, 0.5, "Data coords", transform=ax.transData)

# Axes coordinates (0-1 range)
ax.text(0.5, 0.9, "Axes coords", transform=ax.transAxes, ha='center')

# Figure coordinates (0-1 range)
fig.text(0.5, 0.02, "Figure coords", ha='center')

plt.show()

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Practical Example: Labeling Points

import matplotlib.pyplot as plt
import numpy as np

x = np.array([1, 2, 3, 4, 5])
y = np.array([2, 4, 1, 5, 3])
labels = ['A', 'B', 'C', 'D', 'E']

fig, ax = plt.subplots()
ax.scatter(x, y, s=100)

for xi, yi, label in zip(x, y, labels):
    ax.text(xi + 0.1, yi + 0.1, label, fontsize=12, fontweight='bold')

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

---

Multi-line Text

Use newlines for multi-line text:

import matplotlib.pyplot as plt

fig, ax = plt.subplots()
ax.set_xlim(0, 1)
ax.set_ylim(0, 1)

text = """Line 1
Line 2
Line 3"""

ax.text(0.5, 0.5, text, 
        fontsize=12, 
        ha='center', 
        va='center',
        bbox=dict(boxstyle='round', facecolor='wheat'))

plt.show()

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Key Takeaways

• ax.text(x, y, s) adds text at data coordinates
• Use ha and va for alignment
• bbox parameter adds a background box
• transform changes the coordinate system
• LaTeX math is supported with $...$