Enumerate

In both Python and Rust, the enumerate function exists to iterate over a list while keeping track of the index of the current item.

Python

Recall from the first example that we defined a Person class with a name and an age attribute.

We can instantiate a list of Person objects and iterate over them using enumerate.

def run2() -> None:
    persons = [Person("James", 33), Person("Salima", 31)]
    for i, person in enumerate(persons):
        print(f"Person {i}: {str(person)}")

Running the above function via main.py gives us the same output as in Rust:

Person 0: James is 33 years old
Person 1: Salima is 31 years old

The enumerate method returns a tuple of (index, item) for each item in the list, allowing us to access the index of the current item as we iterate over the list in a for loop.

Rust

Recall from the first example that we defined a Person struct with a name and an age attribute, in a similar way to the Python example.

We can instantiate a vector of Person objects and iterate over them using enumerate.

What is a vector? Like many other languages, Rust provides arrays, but arrays in Rust are fixed-size and allocated on the stack. Vectors are dynamic arrays that are allocated on the heap, and can grow and shrink as needed, similar to Python lists.

For most purposes, vectors in Rust perform the same function as Python lists. Unlike a Python list, a vector in Rust can only contain objects of the same type, in this case, Person.

fn run2() {
    let persons = vec![Person::new("James", 33), Person::new("Salima", 31)];
    for (i, p) in persons.iter().enumerate() {
        println!("Person {}: {}", i, p)
    }
}

The vec! macro is syntactic sugar for Vec::new(), which creates a new vector of Person objects. Additionally, the iter method returns an iterator over the vector, which is required before we can call the enumerate method on it.

Running the above function via main.rs gives us the same output as in Python:

Person 0: James is 33 years old
Person 1: Salima is 31 years old

Takeaways

• Both Python and Rust contain a convenience method called enumerate to iterate over a list while keeping track of the index of the current item.
• Python lists are dynamic arrays that can contain objects of any type.
• Rust vectors are heap-allocated dynamic arrays that can only contain objects of the same type.