Writing Python Extensions in Rust with PyO3

Rust’s memory safety comes from the borrow checker, and the borrow checker demands discipline. The learning curve is steep, but the payoff is code that doesn’t crash, doesn’t leak, and doesn’t have data races.

This post covers what makes Rust worth the investment.

The Historical Context

Systems programming has been C and C++ territory for decades. Manual memory management delivered performance but at the cost of safety. Buffer overflows, use-after-free, data races—entire categories of bugs plagued native code.

Rust emerged from Mozilla’s need for a safer systems language. The borrow checker—controversial and demanding—encodes memory safety rules into the type system. What felt restrictive became liberating once you realized: if it compiles, it won’t crash.

The Core Problem

Rust solves the safety vs. performance trade-off. Before Rust, you chose: garbage-collected languages that were safe but slow, or C/C++ that was fast but dangerous. Rust offers both—zero-cost abstractions and compile-time memory safety.

The borrow checker enforces rules about ownership and borrowing. It’s strict, sometimes frustrating, but it catches entire categories of bugs at compile time. The investment in learning pays dividends in production reliability.

A Deep Dive into the Mechanics

Let’s get technical. What’s actually happening under the hood?

At its heart, this concept relies on a few fundamental principles of computer science that we often take for granted. Concepts like idempotency, immutability, and separation of concerns are front and center here.

When implemented correctly, it allows for a level of decoupling that we’ve struggled to achieve with previous generations of tooling. But beware: this power comes with complexity. If you’re not careful, you can easily over-engineer your solution, creating a Rube Goldberg machine that is impossible to debug.

Memory Safety in Practice

The borrow checker isn’t just a compiler feature; it’s a discipline. It forces you to think about object lifecycles upfront.

use std::fmt;

struct Rectangle {
    width: u32,
    height: u32,
}

impl Rectangle {
    fn area(&self) -> u32 {
        self.width * self.height
    }

    fn can_hold(&self, other: &Rectangle) -> bool {
        self.width > other.width && self.height > other.height
    }
}

fn main() {
    let rect1 = Rectangle { width: 30, height: 50 };
    let rect2 = Rectangle { width: 10, height: 40 };

    println!("rect1 is {:?}", rect1); // Requires #[derive(Debug)] normally
    println!(
        "The area of the rectangle is {} square pixels.",
        rect1.area()
    );

    if rect1.can_hold(&rect2) {
        println!("The larger rectangle can hold the smaller one.");
    }
}

By enforcing ownership, we eliminate entire classes of bugs at compile time. No more segfaults, no more data races. Just clean, performant code.

Common Pitfalls

Rust’s learning curve is the obvious pitfall. Fighting the borrow checker for weeks can be demoralizing. The solution is embracing the compiler as a teacher, not an obstacle. Each error is showing you something about memory safety.

Also, don’t try to write Rust like you write Python or Java. Ownership-based design requires different patterns. Learn Rust idioms before trying to build complex systems.

Final Thoughts

Rust’s memory safety guarantees are revolutionary. The borrow checker is strict, but it catches entire classes of bugs at compile time. The learning curve is an investment; the payoff is code that doesn’t crash or leak.

Keep building. Keep learning.