REST is the underlying architectural principle of the web. The amazing thing about the web is the fact that clients (browsers) and servers can interact in complex ways without the client knowing anything beforehand about the server and the resources it hosts. The key constraint is that the server and client must both agree on the media used, which in the case of the web is HTML.
An API that adheres to the principles of REST does not require the client to know anything about the structure of the API. Rather, the server needs to provide whatever information the client needs to interact with the service. An HTML form is an example of this: The server specifies the location of the resource and the required fields. The browser doesn't know in advance where to submit the information, and it doesn't know in advance what information to submit. Both forms of information are entirely supplied by the server. (This principle is called HATEOAS: Hypermedia As The Engine Of Application State.)
So, how does this apply to HTTP, and how can it be implemented in practice? HTTP is oriented around verbs and resources. The two verbs in mainstream usage are GET
and POST
, which I think everyone will recognize. However, the HTTP standard defines several others such as PUT
and DELETE
. These verbs are then applied to resources, according to the instructions provided by the server.
For example, Let's imagine that we have a user database that is managed by a web service. Our service uses a custom hypermedia based on JSON, for which we assign the mimetype application/json+userdb
(There might also be an application/xml+userdb
and application/whatever+userdb
- many media types may be supported). The client and the server have both been programmed to understand this format, but they don't know anything about each other. As Roy Fielding points out:
A REST API should spend almost all of its descriptive effort in
defining the media type(s) used for representing resources and driving
application state, or in defining extended relation names and/or
hypertext-enabled mark-up for existing standard media types.
A request for the base resource /
might return something like this:
Request
GET /
Accept: application/json+userdb
Response
200 OK
Content-Type: application/json+userdb
{
"version": "1.0",
"links": [
{
"href": "/user",
"rel": "list",
"method": "GET"
},
{
"href": "/user",
"rel": "create",
"method": "POST"
}
]
}
We know from the description of our media that we can find information about related resources from sections called "links". This is called Hypermedia controls. In this case, we can tell from such a section that we can find a user list by making another request for /user
:
Request
GET /user
Accept: application/json+userdb
Response
200 OK
Content-Type: application/json+userdb
{
"users": [
{
"id": 1,
"name": "Emil",
"country: "Sweden",
"links": [
{
"href": "/user/1",
"rel": "self",
"method": "GET"
},
{
"href": "/user/1",
"rel": "edit",
"method": "PUT"
},
{
"href": "/user/1",
"rel": "delete",
"method": "DELETE"
}
]
},
{
"id": 2,
"name": "Adam",
"country: "Scotland",
"links": [
{
"href": "/user/2",
"rel": "self",
"method": "GET"
},
{
"href": "/user/2",
"rel": "edit",
"method": "PUT"
},
{
"href": "/user/2",
"rel": "delete",
"method": "DELETE"
}
]
}
],
"links": [
{
"href": "/user",
"rel": "create",
"method": "POST"
}
]
}
We can tell a lot from this response. For instance, we now know we can create a new user by POST
ing to /user
:
Request
POST /user
Accept: application/json+userdb
Content-Type: application/json+userdb
{
"name": "Karl",
"country": "Austria"
}
Response
201 Created
Content-Type: application/json+userdb
{
"user": {
"id": 3,
"name": "Karl",
"country": "Austria",
"links": [
{
"href": "/user/3",
"rel": "self",
"method": "GET"
},
{
"href": "/user/3",
"rel": "edit",
"method": "PUT"
},
{
"href": "/user/3",
"rel": "delete",
"method": "DELETE"
}
]
},
"links": {
"href": "/user",
"rel": "list",
"method": "GET"
}
}
We also know that we can change existing data:
Request
PUT /user/1
Accept: application/json+userdb
Content-Type: application/json+userdb
{
"name": "Emil",
"country": "Bhutan"
}
Response
200 OK
Content-Type: application/json+userdb
{
"user": {
"id": 1,
"name": "Emil",
"country": "Bhutan",
"links": [
{
"href": "/user/1",
"rel": "self",
"method": "GET"
},
{
"href": "/user/1",
"rel": "edit",
"method": "PUT"
},
{
"href": "/user/1",
"rel": "delete",
"method": "DELETE"
}
]
},
"links": {
"href": "/user",
"rel": "list",
"method": "GET"
}
}
Notice that we are using different HTTP verbs (GET
, PUT
, POST
, DELETE
etc.) to manipulate these resources, and that the only knowledge we presume on the client's part is our media definition.
Further reading:
(This answer has been the subject of a fair amount of criticism for missing the point. For the most part, that has been a fair critique. What I originally described was more in line with how REST was usually implemented a few years ago when I first wrote this, rather than its true meaning. I've revised the answer to better represent the real meaning.)
I don't actually think that DI/IoC are that uncommon in Python. What is uncommon, however, are DI/IoC frameworks/containers.
Think about it: what does a DI container do? It allows you to
- wire together independent components into a complete application ...
- ... at runtime.
We have names for "wiring together" and "at runtime":
- scripting
- dynamic
So, a DI container is nothing but an interpreter for a dynamic scripting language. Actually, let me rephrase that: a typical Java/.NET DI container is nothing but a crappy interpreter for a really bad dynamic scripting language with butt-ugly, sometimes XML-based, syntax.
When you program in Python, why would you want to use an ugly, bad scripting language when you have a beautiful, brilliant scripting language at your disposal? Actually, that's a more general question: when you program in pretty much any language, why would you want to use an ugly, bad scripting language when you have Jython and IronPython at your disposal?
So, to recap: the practice of DI/IoC is just as important in Python as it is in Java, for exactly the same reasons. The implementation of DI/IoC however, is built into the language and often so lightweight that it completely vanishes.
(Here's a brief aside for an analogy: in assembly, a subroutine call is a pretty major deal - you have to save your local variables and registers to memory, save your return address somewhere, change the instruction pointer to the subroutine you are calling, arrange for it to somehow jump back into your subroutine when it is finished, put the arguments somewhere where the callee can find them, and so on. IOW: in assembly, "subroutine call" is a Design Pattern, and before there were languages like Fortran which had subroutine calls built in, people were building their own "subroutine frameworks". Would you say that subroutine calls are "uncommon" in Python, just because you don't use subroutine frameworks?)
BTW: for an example of what it looks like to take DI to its logical conclusion, take a look at Gilad Bracha's Newspeak Programming Language and his writings on the subject:
Best Solution
Based on my research, here are some architectural review checklists I've found that do this question a little more justice, and provide some background on what an architecture review is. (Seems to be a bit of confusion about it here.)
Each of these potential candidates include a number of different categories. The overall importance of these categories will vary somewhat depending on business needs. IMHO, that's OK. It's much less costly to ask another question when going through a checklist for a review and rule it out than it is to miss a question or category entirely because it didn't seem important enough to include on a checklist initially.
There also appears to be a white-paper written on this topic, although I have not read it. It attempts to answer this question over the course of about 11 pages.
Additionally a colleague recommended a set of books from Springer, though I have not checked any of these out myself: