Text placement with ax.text in Matplotlib - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the ax.text function do in matplotlib?

It adds text at a specific position on the plot, defined by x and y coordinates.

beginner

Which parameters are essential for placing text using ax.text?

The essential parameters are x and y for position, and s for the text string.

beginner

How can you change the color and font size of text added with ax.text?

Use the color parameter to set text color and fontsize to set the size.

intermediate

What does the ha and va parameters control in ax.text?

ha controls horizontal alignment (left, center, right), and va controls vertical alignment (top, center, bottom) of the text.

beginner

Why is ax.text useful in data visualization?

It helps add labels, notes, or explanations directly on the plot to make the data easier to understand.

Which of these is the correct way to add text at position (2, 3) with the text 'Hello' using ax.text?

A ax.text('Hello', 2, 3)

B ax.text(2, 3, 'Hello')

C ax.text('Hello')

D ax.text(3, 2, 'Hello')

The correct syntax is ax.text(x, y, s), so ax.text(2, 3, 'Hello') places 'Hello' at x=2, y=3.

How do you align text to the center horizontally using ax.text?

A ha='center'

B va='center'

C align='center'

D text_align='center'

The parameter ha='center' sets horizontal alignment to center.

Which parameter changes the font size of text in ax.text?

A textsize

B fontweight

C fontsize

D size

The fontsize parameter controls the size of the text font.

What does the 'va' parameter control in ax.text?

A Vertical alignment of the text

B Value of the text

C Visibility of the text

D Variable alignment

The va parameter controls vertical alignment (top, center, bottom) of the text.

If you want to add red text at coordinates (1, 1), which is the correct code?

A ax.text(1, 1, 'Text', textcolor='red')

B ax.text(1, 1, 'Text', fontcolor='red')

C ax.text('Text', 1, 1, color='red')

D ax.text(1, 1, 'Text', color='red')

The color parameter sets the text color, so ax.text(1, 1, 'Text', color='red') is correct.

Explain how to place and style text on a matplotlib plot using ax.text.

Think about position, what you want to say, and how it looks.

Describe why adding text annotations with ax.text can improve a data visualization.

Imagine you are telling a story with your plot.

Practice

1. What does the ax.text function do in matplotlib?

easy

A. It draws a line between two points.

B. It places text at specified x and y coordinates on the plot.

C. It creates a new figure window.

D. It changes the background color of the plot.

Solution

1. Step 1: Understand the purpose of ax.text

   The ax.text function is used to add text labels at specific positions on a plot using x and y coordinates.

2. Step 2: Compare with other options

   Other options describe different matplotlib functions: creating figures, drawing lines, or changing background color, which are not what ax.text does.

3. Final Answer:

   It places text at specified x and y coordinates on the plot. -> Option B

4. Quick Check:

   ax.text adds text labels = C [OK]

Hint: ax.text adds text at (x, y) on the plot [OK]

Common Mistakes:

• Confusing ax.text with plot or figure functions
• Thinking ax.text changes plot colors
• Assuming ax.text draws shapes

2. Which of the following is the correct syntax to place the text 'Hello' at coordinates (2, 3) using ax.text?

easy

A. ax.text(2, 3, 'Hello')

B. ax.text('Hello', 2, 3)

C. ax.text(x=3, y=2, text='Hello')

D. ax.text(3, 2, 'Hello')

Solution

1. Step 1: Recall ax.text parameter order

   The correct order is ax.text(x, y, text), so x=2, y=3, text='Hello' means ax.text(2, 3, 'Hello').

2. Step 2: Check other options

   ax.text('Hello', 2, 3) swaps text and coordinates, ax.text(x=3, y=2, text='Hello') uses wrong parameter names, ax.text(3, 2, 'Hello') swaps x and y values.

3. Final Answer:

   ax.text(2, 3, 'Hello') -> Option A

4. Quick Check:

   ax.text(x, y, text) = A [OK]

Hint: Remember ax.text(x, y, text) order [OK]

Common Mistakes:

• Swapping x and y coordinates
• Putting text before coordinates
• Using wrong parameter names

3. What will the following code display on the plot?

import matplotlib.pyplot as plt
fig, ax = plt.subplots()
ax.plot([1, 2, 3], [4, 5, 6])
ax.text(2, 5, 'Center', fontsize=12, color='red')
plt.show()

medium

A. An error because color must be uppercase.

B. A blue text 'Center' at point (2, 5) on the plot.

C. No text will appear because fontsize is missing.

D. A red text 'Center' at point (2, 5) on the plot.

Solution

1. Step 1: Analyze ax.text parameters

   The code places text 'Center' at (2, 5) with font size 12 and color red, which is valid syntax.

2. Step 2: Understand matplotlib behavior

   Text appears on the plot at the given coordinates with specified style. Color names are case-insensitive, so 'red' works fine.

3. Final Answer:

   A red text 'Center' at point (2, 5) on the plot. -> Option D

4. Quick Check:

   ax.text with color='red' shows red text = A [OK]

Hint: Color names in ax.text are case-insensitive [OK]

Common Mistakes:

• Thinking fontsize is mandatory to show text
• Assuming color must be uppercase
• Expecting text at wrong coordinates

4. Identify the error in this code snippet:

fig, ax = plt.subplots()
ax.text(1, 2, fontsize='large')
plt.show()

medium

A. plt.show() must come before ax.text.

B. ax.text requires x and y as strings, not numbers.

C. The text argument is missing.

D. fontsize must be an integer or float, not a string like 'large'.

Solution

1. Step 1: Check ax.text parameters

   Matplotlib's ax.text requires three positional arguments: x, y, and text (s). The code provides only x=1, y=2, then a keyword argument, missing the text.

2. Step 2: Verify other options

   Numbers for x/y are correct, fontsize='large' is valid, and plt.show() order is fine.

3. Final Answer:

   The text argument is missing. -> Option C

4. Quick Check:

   ax.text requires x, y, text = C [OK]

Hint: ax.text requires x, y, text positional args [OK]

Common Mistakes:

• Omitting the text argument
• Confusing parameter order
• Calling plt.show() too early

5. You want to add a label 'Max Point' exactly above the highest point in this plot:

import matplotlib.pyplot as plt
x = [1, 2, 3, 4]
y = [2, 5, 1, 7]
fig, ax = plt.subplots()
ax.plot(x, y, marker='o')
# Add text here
plt.show()

Which code correctly places the label 0.3 units above the highest point?

hard

A. ax.text(4, 7.3, 'Max Point', va='bottom', ha='center')

B. ax.text(4, 7.3, 'Max Point', ha='center')

C. ax.text(4, 7, 'Max Point', va='top')

D. ax.text(4, 7, 'Max Point', ha='left')

Solution

1. Step 1: Identify highest point coordinates

   The highest y value is 7 at x=4.

2. Step 2: Place text 0.3 units above with correct alignment

   To place text above, y=7.3 is correct. Use vertical alignment va='bottom' so text bottom aligns at 7.3, placing text above the point. Horizontal alignment ha='center' centers text horizontally at x=4.

3. Final Answer:

   ax.text(4, 7.3, 'Max Point', va='bottom', ha='center') -> Option A

4. Quick Check:

   Text above point uses y+offset and va='bottom' = B [OK]

Hint: Use va='bottom' to place text above y coordinate [OK]

Common Mistakes:

• Using va='top' places text below the coordinate
• Not adding offset to y coordinate
• Misaligning text horizontally