"a dependent consumer

a declaration of a component's dependencies, defined as interface contracts

an injector (sometimes referred to as a provider or container) that creates instances of classes that implement a given dependency interface on request."

Wait, I still have to declare dependencies, just like the import statement in python, require.js in JS, etc. which are apparently not 'dependency injection' systems? And this just adds, er more code?

That same wikipedia page mentions dynamically loaded dependencies while also mentioning 'a declaration of a components dependencies' which sure doesn't sound dynamic to me.

Does anyone care to provide a better explanation of what dependency injection gives me over the existing common dependency mechanisms?

DI is not the same as an IOC container. Get it right ffs, if you want people to take you seriously.

DI:

    class Blah():
      def __init__(self, dependency):
        self.dep = depedency

    my_blah = container.resolve(Blah)

    "Pinject is a pythonic dependency injection library. Python ports of other libraries, like 
     Spring or Guice, retain the feel (and verbosity) of being designed for a statically typed
     language. Pinject was designed from the ground up for python."

Intuitive.

Also, what's wrong with annotations? I'm rather fond of this sort of code:

    ### implements, resolve, Scope
    class IType(object):
      prop1 = None
      def call(self):
        pass

    @implements(IType)
    class ImplType(object):
      prop1 = "Value"
      def call(self):
        pass

    scope = Scope()
    scope.register(ImplType)

    @resolve(scope)
    class UsesType(object):
      def __init__(self, t=IType):
        self.t = t

    instance = UsesType()

    obj_graph = pinject.new_object_graph(binding_specs=[SomeBindingSpec()])
    needs_provider = obj_graph.provide(NeedsProvider)

    instance = UsesType(my_mock)

    ?????? 

Self important library is self important. Not amazed.

    def python_di_copyright_2069_hosay123(dep, *args, **kwargs):
        modname, _, classname = dep.rpartition('.')
        mod = importlib.import_module(modname)
        return getattr(mod, classname)(*args, **kwargs)

We just published it under Google's Github to give a terrible project implied legitimacy that it likely doesn't even have internally.

If my objects get injected to each other automatically by their name then my dependencies are just as predetermined, which results in coupled code, except the coupling is now difficult to read or modify.

Once I decided I am only using explicit injection, I don't need a framework, I just instantiate my classes in the right order and pass them into each other. What can possibly be more pythonic than that?

I have the same issue with Angular.js btw. They are trying to make is easy to start by adding dependency injection magic, but in reality all I see is "this can't possibly work (and indeed it doesn't)", so I just need to spend more time digging and understanding the magic before I can start writing ANY code.

Every documentation should start by explaining the explicit way of doing things, then adding the sugar afterwards.

import this

From a testing perspective I sort-of get it; from a "this is less tightly coupled" I don't: all you've done is move the coupling to a different level. Code always has to be coupled at some level, so where's the advantage?

With the amount of noise about DI I'm sure it's something I should pay attention to rather than be turned off (as happened with Rails), but I really don't et it. Can anyone provide the missing piece in my thinking?

[0] http://till.klampaeckel.de/blog/archives/154-Dependency-Inje...

+

Implicit class bindings

...ummm...

  Pinject creates implicit bindings for classes.
  The implicit bindings assume your code follows PEP8
  conventions: your classes are named in CamelCase, and
  your args are named in lower_with_underscores. Pinject
  transforms class names to injectable arg names by
  lowercasing words and connecting them with underscores.
  It will also ignore any leading underscore on the class
  name.

  If two classes map to the same arg name, whether those
  classes are in the same module or different modules,
  Pinject will not create an implicit binding for that arg
  name (though it will not raise an error).

not sure if i overlooked it in the notes or not, but i have a couple questions.

you mentioned copyright at the end. what sort of license are you releasing it under?

Does it support nested creation of objects? ( ie if you ask for an instance of class 'FOO' and FOO has a DI or 'BAR' will BAR be first created and then injected into FOO)

That's not IOC. That's service location. Which is only used at the "composition root" (look it up) in IOC.

"In fact, pinject doesn't even mention tests in its documentation. Whew~ That's only the whole reason for using DI in the first place."

No, testing accounts for just one of the more minor reasons to be using DI.

We've repeatedly seen concepts that were popularized by the enterprise Java crowd flow down to the .NET crowd, and eventually to the PHP crowd.

IoC and DI is a good example of this. It was extremely hyped within the Java community during the early- and mid-2000s. Then this flowed into the C# community, with it getting a lot of attention during the late-2000s and early-2010s. Now it has finally made its way to the PHP community.

An astute PHP user who recognizes this flow of ideas will look at how the trend has progressed within the Java and C# communities. What they'll see is that there has be movement away from IoC and DI. The purported advantages never materialized, but there was a lot of pain and bad code left around.

Many in the Java community have moved on toward simpler frameworks and techniques, or even toward a far more static JVM-targeting language like Scala. Many C# users have similarly started moving away to other approaches.

At some point, perhaps around 2016 or so, the PHP community will come to the same conclusions about the suitability (or lack thereof) of these techniques. After experiencing the problems first hand, they'll too move back to simpler, more explicit approaches.

read "Dependency injection in .Net" by Mark Seemann. it's the best resource to understand wtf DI is all about and what are benefits.