Cursor and event handling in Matplotlib - Time & Space Complexity

Time Complexity: Cursor and event handling

O(n)

Understanding Time Complexity

When using cursor and event handling in matplotlib, it is important to understand how the program's speed changes as more events happen.

We want to know how the time to respond grows when many events occur.

Scenario Under Consideration

Analyze the time complexity of the following code snippet.

import matplotlib.pyplot as plt

fig, ax = plt.subplots()
line, = ax.plot([0, 1, 2], [0, 1, 0])

def on_move(event):
    if event.inaxes:
        x, y = event.xdata, event.ydata
        print(f"Cursor at: ({x:.2f}, {y:.2f})")

cid = fig.canvas.mpl_connect('motion_notify_event', on_move)
plt.show()

This code sets up a plot and prints the cursor position whenever the mouse moves inside the plot area.

Identify Repeating Operations

Identify the loops, recursion, array traversals that repeat.

• Primary operation: The event handler on_move runs every time the mouse moves inside the plot.
• How many times: It runs once per mouse movement event, which can be many times per second.

How Execution Grows With Input

As the number of mouse movements increases, the number of times on_move runs also increases directly.

Input Size (n)	Approx. Operations
10	10 calls to on_move
100	100 calls to on_move
1000	1000 calls to on_move

Pattern observation: The number of operations grows linearly with the number of mouse events.

Final Time Complexity

Time Complexity: O(n)

This means the time to handle events grows directly with the number of mouse movements.

Common Mistake

[X] Wrong: "The event handler runs only once, so time does not grow with more mouse moves."

[OK] Correct: The handler runs every time the mouse moves, so more moves mean more calls and more time.

Interview Connect

Understanding how event handling scales helps you write responsive and efficient interactive plots, a useful skill in data visualization tasks.

Self-Check

What if we added a loop inside the event handler that processes a list of size m? How would the time complexity change?