DI is Dependency Injection, which is a $1,000 term for a $5 concept.

A Python class without DI:

    class SomeClass(object):
        def __init__(self):
            self.someDependency = GetDependency()

A Python class WITH DI:

    class SomeClass(object):
        def __init__(self, dependency):
            self.someDependency = dependency

...

That's it. DI is just explicitly passing ("injecting") a dependent object into an object, rather than requiring the object to call a function to get a reference/pointer to the dependency or make one.