Flask is a REST engine written in Python. Pretty much like Django, however much simpler. It is very suitable for exposing microservices, with a small number of controllers etc. Here is a sample of how to do stuff with Flask. <\/p>\n\n\n\n\n\n\n\n
Import: to use it, you have to install the package with pip, the packge name is flask;<\/p>\n\n\n\n
The g object is accessed with flask.g and it is an object that is isolated in a request \/ response cycle. You add stuff in it, then get it wherever you need it and then read the previously set attributes. It is like a dictionary, so update it with whatever key \/ value pairs you want. <\/p>\n\n\n\n
One very good example: the general configuration data is one thing, the db connection pool is another thing that can be set <\/p>\n\n\n\n
Here is an example of an application with a controller associated with that flask application instance<\/p>\n\n\n\n
import<\/span> flask<\/span>\n\n\ndef<\/span> start<\/span>():\n app =<\/span> flask.<\/span>Flask(__name__)\n\n @app<\/span>.<\/span>route('\/'<\/span>, methods=<\/span>['GET'<\/span>])\n def<\/span> alfa<\/span>():\n return<\/span> "the response"<\/span>\n\n app.<\/span>run('0.0.0.0'<\/span>, 8080<\/span>)\n\n\nif<\/span> __name__ ==<\/span> '__main__'<\/span>:\n start()\n<\/pre><\/div>\n\n\n\nSo you see the following:<\/p>\n\n\n\n
\n- application is defined<\/li>\n\n\n\n
- @app is related to the flask application stored in variable app, different variable, different annotation<\/li>\n\n\n\n
- @app.route registers route “\/” for method GET for the function alfa<\/li>\n<\/ul>\n\n\n\n
In the end all the requests on the server at port 8080 shall be processed by this function<\/p>\n\n\n\n
Hello world sample without annotation<\/h2>\n\n\n\n
In the above example there is a small problem: you need to define the function alfa inside a context that has all defined, app, etc. This is an issue: a project with 100 controllers, each exposing different route etc cannot be practically devised in this way: at least each controller function should be defined in a different file, to look more elegant etc. OK. So how do you programmatically add a route to a flask application, well, in this way: <\/p>\n\n\n\n
import<\/span> flask<\/span>\n\n\ndef<\/span> alpha<\/span>():\n return<\/span> "the response"<\/span>\n\n\ndef<\/span> start<\/span>():\n app =<\/span> flask.<\/span>Flask(__name__)\n\n app.<\/span>add_url_rule('\/'<\/span>, 'root'<\/span>, alpha, methods=<\/span>['GET'<\/span>])\n\n app.<\/span>run('0.0.0.0'<\/span>, 8080<\/span>)\n\n\nif<\/span> __name__ ==<\/span> '__main__'<\/span>:\n start()\n<\/pre><\/div>\n\n\n\nSimple: function alpha is defined elsewhere; it is now in our file for simplicity but typically for bigger applications it is moved in a totally different file. <\/p>\n\n\n\n
Setting response status code and headers<\/h2>\n\n\n\n
In the method alpha defined above, instead of merely returning a string, better create a response from flask and then modify the state of this response by adding headers and overriding the status code – which normally is 200, here:<\/p>\n\n\n\n
def<\/span> alpha<\/span>():\n resp =<\/span> flask.<\/span>Response("the response"<\/span>)\n resp.<\/span>headers.<\/span>update({'Content-Type'<\/span>: 'text'<\/span>})\n resp.<\/span>status_code =<\/span> 206<\/span>\n\n return<\/span> resp\n<\/pre><\/div>\n\n\n\nBefore request and after request<\/h2>\n\n\n\n
Many times you need to have something done before any request is being transferred to the route processors. A good example is either to get the actual start of the transaction for metrics, or to get the g object and put some stuff in it to be available for downstream processing. <\/p>\n\n\n\n
This is how you define a function that is used before any request: <\/p>\n\n\n\n
def<\/span> call_before_request<\/span>():\n print<\/span>('before request'<\/span>)\n\n\ndef<\/span> call_after_request<\/span>(response):\n print<\/span>('after request'<\/span>)\n return<\/span> response\n\n\ndef<\/span> start<\/span>():\n app =<\/span> flask.<\/span>Flask(__name__)\n\n app.<\/span>add_url_rule('\/'<\/span>, 'root'<\/span>, alpha, methods=<\/span>['GET'<\/span>])\n app.<\/span>before_request_funcs[None<\/span>] =<\/span> [call_before_request]\n app.<\/span>after_request_funcs[None<\/span>] =<\/span> [call_after_request]\n\n app.<\/span>run('0.0.0.0'<\/span>, 8080<\/span>)\n<\/pre><\/div>\n\n\n\nPlease note:<\/p>\n\n\n\n
\n- you can use very well annotation before_request and after_reqeust but again, the functions that are implemented for this purpose must be defined in a context where app is easy to access<\/li>\n\n\n\n
- very important, the call after request gets the http response as a parameter and must return this response (after you did or you did not changes to it) or else you get http code 500<\/li>\n\n\n\n
- definitely the fact that we wrote some print statements inside those function is only for demo purposes; normally you use either logging or you just don’t print stuff from those functions. <\/li>\n<\/ul>\n","protected":false},"excerpt":{"rendered":"
Flask is a REST engine written in Python. Pretty much like Django, however much simpler. It is very suitable for exposing microservices, with a small number of controllers etc. Here is a sample of how to do stuff with Flask.<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[],"class_list":["post-24","post","type-post","status-publish","format-standard","hentry","category-uncategorized"],"_links":{"self":[{"href":"https:\/\/coding101.xyz\/index.php?rest_route=\/wp\/v2\/posts\/24","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/coding101.xyz\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/coding101.xyz\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/coding101.xyz\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/coding101.xyz\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=24"}],"version-history":[{"count":5,"href":"https:\/\/coding101.xyz\/index.php?rest_route=\/wp\/v2\/posts\/24\/revisions"}],"predecessor-version":[{"id":99,"href":"https:\/\/coding101.xyz\/index.php?rest_route=\/wp\/v2\/posts\/24\/revisions\/99"}],"wp:attachment":[{"href":"https:\/\/coding101.xyz\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=24"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/coding101.xyz\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=24"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/coding101.xyz\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=24"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}