python-design-pattern-rag

The Prebound Method Pattern (Structural)

Purpose

The Prebound Method pattern improves performance by storing a method reference in a local variable before calling it repeatedly. It’s especially helpful in loops or callback-heavy code, where method lookups would otherwise happen over and over.

Problem It Solves

In Python, each time you call an instance method (e.g., obj.method()), Python performs a dynamic lookup to resolve the method. This is fine for occasional calls, but in tight loops or high-frequency callbacks, this lookup adds unnecessary overhead. By assigning the method to a local variable first, you can avoid the repeated lookup and make calls faster.

When to Use It

Use this pattern when:

• You call the same method many times in a loop or performance-critical section.
• You’re registering the same method as a callback in multiple places.
• You want to optimize by reducing small but repeated overhead.

When Not to Use It

Skip this pattern if:

• The method is only called a few times.
• Readability matters more than micro-optimization.
• The performance gain is too small to justify the extra step.

How It Works

Instead of calling the method like this each time:

obj.method()

You assign it once to a local variable:

method = obj.method

Then use method() directly. In Python, this works because accessing a bound method returns a callable object that includes the instance (self), so you’re effectively storing a preconfigured function.

Real-World Analogy

Think of a librarian who looks up a specific book multiple times. Rather than scanning all the shelves each time, they write the book’s location on a sticky note and go directly to it. That’s what prebinding does—it skips the repeated search.

Simplified Example

class Processor:
    def process_text(self, text):
        print(f"Processing text: {text}")

proc = Processor()

# Prebind the method
process_text = proc.process_text

# Use it multiple times
for _ in range(3):
    process_text("Hello, world!")

By prebinding proc.process_text to process_text, you avoid the repeated attribute lookup during the loop.

Learn More

Explore the full Python example here: Prebound Method Pattern on GitHub

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