Why Figure creation with plt.figure in Matplotlib? - Purpose & Use Cases

The Big Idea

What if your beautiful charts got lost in a messy tangle of lines? Here's how to keep them neat and clear!

The Scenario

Imagine you want to draw multiple pictures on paper, but you only have one sheet. You try to draw everything on that one sheet, and it gets messy and confusing.

The Problem

When you try to plot many charts without creating separate figures, your graphs overlap each other. It becomes hard to see each chart clearly, and fixing this by erasing or redrawing is slow and frustrating.

The Solution

Using plt.figure() lets you create a new blank canvas for each chart. This way, each graph has its own space, making your visuals clear and organized without any overlap.

Before vs After

✗ Before

plt.plot(data1)
plt.plot(data2)  # second plot overlaps the first

✓ After

plt.figure()
plt.plot(data1)
plt.figure()
plt.plot(data2)  # separate figures, no overlap

What It Enables

It allows you to create multiple clear and separate charts easily, making your data stories easier to understand and share.

Real Life Example

A teacher preparing different graphs for a class presentation can create each chart on its own figure, so students see each topic clearly without confusion.

Key Takeaways

Without separate figures, plots can overlap and become unclear.

plt.figure() creates a new blank canvas for each plot.

This keeps charts organized and easy to read.

Practice

1. What does the plt.figure() function do in matplotlib?

easy

A. Plots a line graph directly

B. Creates a new blank canvas for plotting graphs

C. Saves the current plot to a file

D. Displays the plot on the screen

Solution

1. Step 1: Understand the role of plt.figure()

   The plt.figure() function creates a new empty figure, which is like a blank canvas for drawing plots.

2. Step 2: Differentiate from other functions

   Functions like plt.plot() draw on the figure, plt.show() displays it, and plt.savefig() saves it. Only plt.figure() creates the blank space.

3. Final Answer:

   Creates a new blank canvas for plotting graphs -> Option B

4. Quick Check:

   plt.figure() = new blank canvas [OK]

Hint: Remember: figure = blank canvas for plots [OK]

Common Mistakes:

• Confusing plt.figure() with plt.plot()
• Thinking plt.figure() displays the plot
• Assuming plt.figure() saves the plot

2. Which of the following is the correct way to create a figure with size 8 inches wide and 6 inches tall using plt.figure()?

easy

A. plt.figure(size=(8, 6))

B. plt.figure(dimensions=(8, 6))

C. plt.figure(size=[8, 6])

D. plt.figure(figsize=(8, 6))

Solution

1. Step 1: Recall the correct parameter name

   The parameter to set figure size is figsize, which takes a tuple of (width, height) in inches.

2. Step 2: Check the syntax of options

   Only plt.figure(figsize=(8, 6)) uses figsize=(8, 6) correctly. Others use wrong parameter names or data types.

3. Final Answer:

   plt.figure(figsize=(8, 6)) -> Option D

4. Quick Check:

   figsize=(width, height) = plt.figure(figsize=(8, 6)) [OK]

Hint: Use figsize=(width, height) tuple inside plt.figure() [OK]

Common Mistakes:

• Using 'size' instead of 'figsize'
• Passing list instead of tuple
• Using wrong parameter names like 'dimensions'

3. What will be the output of this code?

import matplotlib.pyplot as plt
fig = plt.figure(figsize=(4, 3), dpi=100)
print(fig.get_size_inches())
print(fig.dpi)

medium

A. [4 3]
100.0

B. [400 300]
100.0

C. [4. 3.]
100.0

D. [4.0 3.0]
10

Solution

1. Step 1: Understand figsize and dpi

   The figsize is in inches as a float array, so fig.get_size_inches() returns [4. 3.]. The dpi is dots per inch, set to 100.0.

2. Step 2: Check print outputs

   Printing fig.get_size_inches() shows floats with decimal points. Printing fig.dpi shows 100.0 as set.

3. Final Answer:

   [4. 3.] 100.0 -> Option C

4. Quick Check:

   figsize floats and dpi number = [4. 3.] and 100.0 [OK]

Hint: fig.get_size_inches() returns floats, dpi is float [OK]

Common Mistakes:

• Expecting integers instead of floats for size
• Confusing dpi value with size
• Misreading output format

4. Identify the error in this code snippet:

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

medium

A. The parameter 'size' is invalid; should be 'figsize'

B. plt.plot() cannot be used after plt.figure()

C. plt.show() is missing parentheses

D. The lists in plt.plot() have different lengths

Solution

1. Step 1: Check parameter names in plt.figure()

   The correct parameter to set figure size is figsize, not size. Using size causes an error.

2. Step 2: Verify other parts of the code

   Using plt.plot() after plt.figure() is valid. plt.show() has parentheses. Lists have same length.

3. Final Answer:

   The parameter 'size' is invalid; should be 'figsize' -> Option A

4. Quick Check:

   Use figsize= not size= in plt.figure() [OK]

Hint: Use figsize=, not size=, to set figure size [OK]

Common Mistakes:

• Using 'size' instead of 'figsize'
• Thinking plt.plot() can't follow plt.figure()
• Forgetting parentheses in plt.show()

5. You want to create two separate plots in two separate windows. Which code correctly creates two figures and plots a simple line in each?

hard

A. fig1 = plt.figure(figsize=(4,3))
plt.plot([1,2,3],[4,5,6])
fig2 = plt.figure(figsize=(4,3))
plt.plot([1,2,3],[6,5,4])
plt.show()

B. plt.figure(figsize=(8,3))
plt.subplot(1,2,1)
plt.plot([1,2,3],[4,5,6])
plt.subplot(1,2,2)
plt.plot([1,2,3],[6,5,4])
plt.show()

C. fig = plt.figure(figsize=(8,3))
plt.plot([1,2,3],[4,5,6])
plt.plot([1,2,3],[6,5,4])
plt.show()

D. plt.figure(figsize=(4,3))
plt.plot([1,2,3],[4,5,6])
plt.figure(figsize=(4,3))
plt.plot([1,2,3],[6,5,4])

Solution

1. Step 1: Understand figure creation for multiple plots

   Creating two separate figures requires calling plt.figure() twice, each time creating a new blank canvas.

2. Step 2: Check code correctness

   fig1 = plt.figure(figsize=(4,3)) plt.plot([1,2,3],[4,5,6]) fig2 = plt.figure(figsize=(4,3)) plt.plot([1,2,3],[6,5,4]) plt.show() creates two figures with specified sizes and plots on each before showing. plt.figure(figsize=(8,3)) plt.subplot(1,2,1) plt.plot([1,2,3],[4,5,6]) plt.subplot(1,2,2) plt.plot([1,2,3],[6,5,4]) plt.show() uses subplots in one figure, not two figures. fig = plt.figure(figsize=(8,3)) plt.plot([1,2,3],[4,5,6]) plt.plot([1,2,3],[6,5,4]) plt.show() plots both lines on one figure. plt.figure(figsize=(4,3)) plt.plot([1,2,3],[4,5,6]) plt.figure(figsize=(4,3)) plt.plot([1,2,3],[6,5,4]) misses plt.show().

3. Final Answer:

   fig1 = plt.figure(figsize=(4,3)) plt.plot([1,2,3],[4,5,6]) fig2 = plt.figure(figsize=(4,3)) plt.plot([1,2,3],[6,5,4]) plt.show() -> Option A

4. Quick Check:

   Two plt.figure() calls = two separate plots [OK]

Hint: Call plt.figure() twice for separate plot windows [OK]

Common Mistakes:

• Using subplots instead of separate figures
• Plotting multiple lines on one figure expecting separate windows
• Forgetting plt.show() to display plots