Figure and axes creation in Data Analysis Python - Step-by-Step Execution

Concept Flow - Figure and axes creation

Import matplotlib.pyplot

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Create Figure object

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Add Axes or Subplots to Figure

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Use Axes to plot data

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Show or save the Figure

This flow shows how to import the plotting library, create a figure, add axes to it, plot data on the axes, and finally display or save the figure.

Execution Sample

Data Analysis Python

import matplotlib.pyplot as plt
fig = plt.figure()
ax = fig.add_subplot(111)
ax.plot([1, 2, 3], [4, 5, 6])
plt.show()

This code creates a figure, adds one axes, plots a simple line, and displays the plot window.

Execution Table

Step	Action	Object Created	State/Value	Output/Effect
1	Import matplotlib.pyplot as plt	plt module	Available for use	No visual output
2	Create figure with plt.figure()	Figure object	Empty figure with no axes	No visual output
3	Add subplot 111 to figure	Axes object	One axes added to figure	No visual output
4	Plot data on axes	Line2D object	Line plotted on axes	No visual output
5	Call plt.show()	N/A	Figure window opens	Plot window displays line graph
6	End of script	N/A	All objects remain in memory	Plot window remains open until closed

💡 Script ends after showing the plot window

Variable Tracker

Variable	Start	After Step 2	After Step 3	After Step 4	Final
plt	Not defined	matplotlib.pyplot module	matplotlib.pyplot module	matplotlib.pyplot module	matplotlib.pyplot module
fig	Not defined	Figure object (empty)	Figure object (with 1 axes)	Figure object (with 1 axes and line)	Figure object (with 1 axes and line)
ax	Not defined	Not defined	Axes object (subplot 111)	Axes object (with line plotted)	Axes object (with line plotted)

Key Moments - 3 Insights

Why do we need to create a Figure before adding Axes?

The Figure is the main container for plots. Without it, Axes have no place to live. See execution_table step 2 and 3 where Figure is created first, then Axes are added.

What does '111' mean in add_subplot(111)?

It means 1 row, 1 column, and this is the 1st subplot. This creates a single axes filling the figure. See execution_table step 3.

Why doesn't plotting data immediately show the plot?

Plotting adds data to the Axes but does not display it. plt.show() must be called to open the plot window. See execution_table step 4 vs step 5.

Visual Quiz - 3 Questions

Look at the execution table, what object is created at step 3?

A Figure object

B Line2D object

C Axes object

D plt module

💡 Hint

Check the 'Object Created' column at step 3 in the execution_table.

At which step does the plot window appear?

A Step 3

B Step 5

C Step 4

D Step 2

💡 Hint

Look at the 'Output/Effect' column to find when the figure window opens.

If we skip creating the Figure object, what happens when adding Axes?

A Error because no Figure exists

B Axes are added to a default figure automatically

C Axes are created but not shown

D Plot shows without axes

💡 Hint

The code calls fig.add_subplot(111), so 'fig' must be defined first; skipping causes NameError: name 'fig' is not defined.

Concept Snapshot

import matplotlib.pyplot as plt
fig = plt.figure()  # Create a figure container
ax = fig.add_subplot(111)  # Add one axes (1 row, 1 col, 1st plot)
ax.plot(x, y)  # Plot data on axes
plt.show()  # Display the figure window
Key: Figure holds Axes; Axes hold plots; show() displays all.

Full Transcript

This lesson shows how to create a figure and axes using matplotlib in Python. First, we import matplotlib.pyplot as plt. Then we create a Figure object with plt.figure(). Next, we add an Axes object to the figure using fig.add_subplot(111), which means one row, one column, first subplot. We plot data on the axes with ax.plot(). Finally, plt.show() opens a window displaying the plot. Variables plt, fig, and ax change as we create and add objects. Beginners often wonder why Figure must be created first, what '111' means, and why plotting doesn't immediately show the plot. The execution table traces each step and object creation. The visual quiz tests understanding of these steps. Remember: Figure is the container, Axes is the plot area, and show() displays the figure.