Any need for dependency injection in Dynamic Languages?

In order to write testable C# code, I use DI heavily.

However lately I've been messing around with IronPython and found that as you can mock any methods/classes/functions etc... you like, the need for DI is gone.

Is this the case for dynamic langagues such as Python?

Instead of:

class Person(Address) {
...

You can have:

class Person() {
...
    // Address initialised in here.

For dynamic languages and therefore following manaual DI for dynamic langagues is simply not needed.

Any advice on this?

Solution

Dependency Injection is also about how you wire things together --- which has nothing to do about the mockability of depended-on objects. There's a difference between having a Foo-instance that needs a Bar-connection of some kind instantiate it directly and having it completely ignore how it gets that connection as long as it has it.

If you use dependency injection you also gain better testability. But the converse isn't true. Easier testability by being able to overwrite anything doesn't bring the other advantages of dependency injection. There are many component/DI-frameworks for Python available exactly for these reasons.