Title and axis labels in Matplotlib - Step-by-Step Execution

Concept Flow - Title and axis labels

Start plot

↓

Plot data points

↓

Add title with plt.title()

↓

Add x-axis label with plt.xlabel()

↓

Add y-axis label with plt.ylabel()

↓

Show plot with plt.show()

This flow shows how to create a plot, add a title, label the x and y axes, and then display the plot.

Execution Sample

Matplotlib

import matplotlib.pyplot as plt
x = [1, 2, 3]
y = [4, 5, 6]
plt.plot(x, y)
plt.title('My Plot')
plt.xlabel('X axis')
plt.ylabel('Y axis')
plt.show()

This code plots points, adds a title and axis labels, then displays the plot.

Execution Table

Step	Action	Function Called	Effect on Plot
1	Import matplotlib.pyplot	import matplotlib.pyplot as plt	Prepare plotting functions
2	Define x and y data	x = [1, 2, 3]; y = [4, 5, 6]	Data ready for plotting
3	Plot data points	plt.plot(x, y)	Line connecting points (1,4), (2,5), (3,6) shown
4	Add plot title	plt.title('My Plot')	Title 'My Plot' appears at top
5	Add x-axis label	plt.xlabel('X axis')	Label 'X axis' appears below x-axis
6	Add y-axis label	plt.ylabel('Y axis')	Label 'Y axis' appears beside y-axis
7	Display plot	plt.show()	Plot window opens showing all elements
8	End	N/A	Plot displayed with title and axis labels

💡 Plot is shown with title and axis labels, execution ends.

Variable Tracker

Variable	Start	After Step 2	After Step 3	Final
x	undefined	[1, 2, 3]	[1, 2, 3]	[1, 2, 3]
y	undefined	[4, 5, 6]	[4, 5, 6]	[4, 5, 6]
plt	undefined	matplotlib.pyplot module	matplotlib.pyplot module	matplotlib.pyplot module

Key Moments - 3 Insights

Why do we call plt.title() after plt.plot()?

Calling plt.title() after plt.plot() ensures the title is added to the current plot. The execution_table row 4 shows the title added after plotting data.

What happens if we forget plt.show()?

Without plt.show(), the plot window does not open to display the plot. Execution_table row 7 shows plt.show() triggers the plot display.

Can we add axis labels before plotting data?

Yes, but usually we plot data first to confirm axes exist. The flow shows adding labels after plotting for clarity.

Visual Quiz - 3 Questions

Look at the execution_table at step 4, what is the effect on the plot?

A A title 'My Plot' appears at the top

B X-axis label is added

C Data points are plotted

D Plot window opens

💡 Hint

Check the 'Effect on Plot' column at step 4 in execution_table

At which step does the plot window open to show the plot?

A Step 3

B Step 7

C Step 5

D Step 6

💡 Hint

Look for plt.show() call in the 'Function Called' column in execution_table

If we remove plt.ylabel('Y axis'), what changes in the plot?

A The plot will not show data points

B The plot title will disappear

C The plot will have no y-axis label

D The plot window will not open

💡 Hint

Refer to execution_table step 6 where y-axis label is added

Concept Snapshot

Use plt.title('Title') to add a plot title.
Use plt.xlabel('X label') and plt.ylabel('Y label') to label axes.
Call these after plt.plot() to label the current plot.
Use plt.show() to display the plot window.
Without plt.show(), plot won't appear.

Full Transcript

This lesson shows how to add a title and axis labels to a plot using matplotlib. First, we import matplotlib.pyplot as plt. Then, we define x and y data points. Next, we plot the data with plt.plot(x, y). After plotting, we add a title using plt.title('My Plot'). We label the x-axis with plt.xlabel('X axis') and the y-axis with plt.ylabel('Y axis'). Finally, plt.show() displays the plot window with all these elements. The execution table traces each step and its effect on the plot. Key moments clarify why the order matters and the role of plt.show(). The visual quiz tests understanding of these steps. The snapshot summarizes the commands and their purpose.

Practice

1. Which matplotlib function is used to add a title to a plot?

easy

A. plt.axis()

B. plt.label()

C. plt.legend()

D. plt.title()

Solution

1. Step 1: Understand the purpose of plt.title()

   This function adds a title text at the top of the plot, describing what the plot shows.

2. Step 2: Compare with other functions

   plt.label() does not exist, plt.legend() adds a legend, and plt.axis() controls axis limits, so they don't add a title.

3. Final Answer:

   plt.title() -> Option D

4. Quick Check:

   Title function = plt.title() [OK]

Hint: Title is always set with plt.title() [OK]

Common Mistakes:

• Using plt.label() instead of plt.title()
• Confusing legend with title
• Trying plt.axis() for title

2. Which of the following is the correct syntax to label the x-axis as 'Time (seconds)' in matplotlib?

easy

A. plt.xlabel('Time (seconds)')

B. plt.xaxis('Time (seconds)')

C. plt.label('x', 'Time (seconds)')

D. plt.axislabel('Time (seconds)')

Solution

1. Step 1: Recall the function to label x-axis

   The correct function is plt.xlabel() which takes the label text as argument.

2. Step 2: Check other options for syntax errors

   plt.xaxis(), plt.label(), and plt.axislabel() are not valid matplotlib functions for axis labeling.

3. Final Answer:

   plt.xlabel('Time (seconds)') -> Option A

4. Quick Check:

   X-axis label = plt.xlabel() [OK]

Hint: Use plt.xlabel() for x-axis label text [OK]

Common Mistakes:

• Using plt.xaxis() which doesn't exist
• Trying plt.label() for axis
• Confusing axis limits with labels

3. What will be the output of the following code?

import matplotlib.pyplot as plt
plt.plot([1, 2, 3], [4, 5, 6])
plt.title('Sales Over Time')
plt.xlabel('Month')
plt.ylabel('Sales')
plt.show()

medium

A. A plot with title but no axis labels

B. A plot with no title and no axis labels

C. A plot with title 'Sales Over Time', x-axis labeled 'Month', y-axis labeled 'Sales'

D. A plot with axis labels but no title

Solution

1. Step 1: Analyze the code lines for title and labels

   The code uses plt.title('Sales Over Time') to add a title, plt.xlabel('Month') for x-axis label, and plt.ylabel('Sales') for y-axis label.

2. Step 2: Understand the plot display

   The plot will show the line graph with all these labels visible as specified.

3. Final Answer:

   A plot with title 'Sales Over Time', x-axis labeled 'Month', y-axis labeled 'Sales' -> Option C

4. Quick Check:

   Title and axis labels set correctly [OK]

Hint: Check all label functions called before plt.show() [OK]

Common Mistakes:

• Forgetting plt.title() call
• Mixing up xlabel and ylabel
• Not calling plt.show() to display

4. Identify the error in this code snippet that tries to add a title and axis labels:

import matplotlib.pyplot as plt
plt.plot([1, 2, 3], [3, 2, 1])
plt.title = 'My Plot'
plt.xlabel('X Axis')
plt.ylabel('Y Axis')
plt.show()

medium

A. Using assignment operator '=' instead of function call for plt.title

B. Missing plt.show() call

C. Incorrect order of xlabel and ylabel calls

D. plt.plot() arguments are invalid

Solution

1. Step 1: Check how title is set

   The code uses plt.title = 'My Plot' which assigns a string to the function name, overwriting it instead of calling it.

2. Step 2: Understand correct usage

   The correct way is to call the function: plt.title('My Plot') to set the title.

3. Final Answer:

   Using assignment operator '=' instead of function call for plt.title -> Option A

4. Quick Check:

   Title must be set by calling plt.title() [OK]

Hint: Use parentheses () to call plt.title() function [OK]

Common Mistakes:

• Assigning string to plt.title instead of calling
• Forgetting plt.show()
• Swapping xlabel and ylabel calls

5. You want to create a plot with the title 'Temperature Trends', x-axis labeled 'Day', and y-axis labeled 'Temperature (°C)'. Which code snippet correctly achieves this?

hard

A. plt.plot(days, temps)
plt.title = 'Temperature Trends'
plt.xlabel = 'Day'
plt.ylabel = 'Temperature (°C)'
plt.show()

B. plt.plot(days, temps)
plt.title('Temperature Trends')
plt.xlabel('Day')
plt.ylabel('Temperature (°C)')
plt.show()

C. plt.plot(days, temps)
plt.set_title('Temperature Trends')
plt.set_xlabel('Day')
plt.set_ylabel('Temperature (°C)')
plt.show()

D. plt.plot(days, temps)
plt.title('Temperature Trends')
plt.xaxis('Day')
plt.yaxis('Temperature (°C)')
plt.show()

Solution

1. Step 1: Verify correct function calls for title and labels

   plt.plot(days, temps) plt.title('Temperature Trends') plt.xlabel('Day') plt.ylabel('Temperature (°C)') plt.show() uses plt.title(), plt.xlabel(), and plt.ylabel() correctly with parentheses and proper arguments.

2. Step 2: Check other options for errors

   plt.plot(days, temps) plt.title = 'Temperature Trends' plt.xlabel = 'Day' plt.ylabel = 'Temperature (°C)' plt.show() incorrectly assigns strings to functions, plt.plot(days, temps) plt.set_title('Temperature Trends') plt.set_xlabel('Day') plt.set_ylabel('Temperature (°C)') plt.show() uses non-existent set_title functions, and plt.plot(days, temps) plt.title('Temperature Trends') plt.xaxis('Day') plt.yaxis('Temperature (°C)') plt.show() uses invalid xaxis and yaxis functions.

3. Final Answer:

   plt.plot(days, temps) plt.title('Temperature Trends') plt.xlabel('Day') plt.ylabel('Temperature (°C)') plt.show() -> Option B

4. Quick Check:

   Use plt.title(), plt.xlabel(), plt.ylabel() with parentheses [OK]

Hint: Always call plt.title(), plt.xlabel(), plt.ylabel() as functions [OK]

Common Mistakes:

• Assigning labels instead of calling functions
• Using non-existent set_title() methods
• Using plt.xaxis() instead of plt.xlabel()