Mojo Lists

Mojo Lists vs Python Lists

Mojo seeks to provide a familar programming model to python programmers, while allowing them the option of using more performant low level constructs. The stdlib is similar to python stdlib, but not exactly the same.

Iterating over lists

Python

a: List[int] = [1, 2, 3, 4]
for e in a:
    print(a)

Mojo

var a: List[Int] = List(1, 2, 3, 4)
for e in a:
    print(e)

Fails with hard to understand type errors on print().

So the programmer is forced to write:

var a: List[Int] = List(1, 2, 3, 4)
for i in range(a.size):
    var e = a[i]
    print(e)

Comparing Lists

Python

a = [1, 2, 3]
b = [4, 5, 6]
c = [4, 5, 6]
assert a != b
assert b == c

Mojo

import testing

var a: List[Int] = List(1, 2, 3)
var b: List[Int] = List(4, 5, 6)
var c: List[Int] = List(4, 5, 6)

testing.assert_not_equal(a, b)
testing.assert_equal(b, c)

Fails with List doesn’t implement __eq__ or __ne__.

Summary

While mojo makes a good faith attempt to be approachable to python programmers, it has gaps in the API and error messages can be hard to decipher for the average python programmer.