Text placement with ax.text in Matplotlib - Mini Project: Build & Apply

Text placement with ax.text

📖 Scenario: You are creating a simple plot to show the sales of a small shop over three days. You want to add text labels on the plot to clearly show the sales numbers on each day.

🎯 Goal: Build a plot using matplotlib that shows sales data for three days and place text labels on the plot using ax.text to display the sales numbers above each point.

📋 What You'll Learn

Create a plot with three points representing sales on three days

Use ax.text to place text labels showing sales numbers

Position the text labels slightly above each point for clarity

Print the final plot with the text labels visible

💡 Why This Matters

🌍 Real World

Adding text labels to plots helps make data easier to understand in reports and presentations.

💼 Career

Data scientists and analysts often annotate plots to highlight important values or trends for stakeholders.

1

Create the sales data and plot points

Create a list called days with values [1, 2, 3] representing three days. Create a list called sales with values [100, 150, 120] representing sales for each day. Then create a plot using fig, ax = plt.subplots() and plot the sales data as points using ax.plot(days, sales, 'o').

Matplotlib

import matplotlib.pyplot as plt
# Create days and sales lists
# Create the plot and plot the points
# Your code here

Hint

Use plt.subplots() to create the plot and ax.plot() to plot points.

2

Set vertical offset for text labels

Create a variable called offset and set it to 5. This will be used to position the text labels slightly above the points.

Matplotlib

import matplotlib.pyplot as plt

days = [1, 2, 3]
sales = [100, 150, 120]

fig, ax = plt.subplots()
ax.plot(days, sales, 'o')
# Create offset variable
# Your code here

Hint

Just create a variable named offset and assign it the value 5.

3

Add text labels above each point

Use a for loop with variables day and sale to iterate over zip(days, sales). Inside the loop, use ax.text(day, sale + offset, str(sale)) to place the sales number as text slightly above each point.

Matplotlib

import matplotlib.pyplot as plt

days = [1, 2, 3]
sales = [100, 150, 120]

fig, ax = plt.subplots()
ax.plot(days, sales, 'o')
offset = 5
# Add text labels above each point
# Your code here

Hint

Use zip(days, sales) to loop over both lists together and ax.text() to add text.

4

Display the plot with text labels

Write plt.show() to display the plot with the points and text labels.

Matplotlib

import matplotlib.pyplot as plt

days = [1, 2, 3]
sales = [100, 150, 120]

fig, ax = plt.subplots()
ax.plot(days, sales, 'o')
offset = 5

for day, sale in zip(days, sales):
    ax.text(day, sale + offset, str(sale))
# Display the plot
# Your code here

Hint

Use plt.show() to display the plot window.

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