I am new to Python (somehow I started looking at python 2 days ago).
I tried to write a simple interactive webpage with CGI, and I used HTML form to get user input. However, as everyone knows, if I refresh the webpage, the form data will be resubmitted again. I just have no idea how to prevent this from happening.
The same problem, but in php/javascript, has been discussed and solutions can be found, but I would like to find the answer to the python case.
I hope there is someone here who can address my problem. Since I am not quite familiar with the language, I hope that, instead of solely giving me a descriptive solution, the kind one can also give me the pieces of codes necessary.
Thank you very much
Your question is not Python-specific, it's about the general web application design patterns.
Use GETs for requests that do not change the web app's state (viewing, queries and so on). Render the page in the response.
Use POST for whatever request that modifies the state (post submitting, editing, deleting).
Never render anything in the response, provide a 303 See Other redirection to the page where the results of the POST can be seen. E.g., if the user added a comment on the page http://example.com/blog/123, the POST handler can be http://example.com/submitcomment, but it should return nothing but a redirection to http://example.com/blog/123#comment5.
That's what #mikep referred to as Post-Redirect-Get.
On the related note: do yourself a favor, skip CGI. There is a number of nice and clean web frameworks for Python. Try Flask or Bottle (smaller frameworks) or go straight to Django if you are building a big app. Search here on Stack Overflow for pros and cons of different frameworks.
Just skip CGI. It's hard to build a good and maintainable CGI app, there are too many things to take care of, things that are already thought if in the frameworks.
I've been wasting time supporting a CGI application for some time, and switching to a framework was a relief.
You might want to view these lectures: http://www.udacity.com/overview/Course/cs253/CourseRev/apr2012
Week 2 will address your queries.
Take a look at POST-REDIRECT-GET web programming patern.
Related
I am looking to create a very basic website that has a single feature. This feature works as follows:
1) The user inputs a URL to a website
2) My website will scrape the given website for necessary information
3) Apply whatever logic I need and return the processed information as a string
4) Allow user to download returned data in .txt format.
I am working on this project with one collaborator, and he has created the scraping and logic (steps 2 and 3) in Python. I have looked around stack overflow to see if it is possible to execute python scripts in a website, and the consensus seemed to be that I will require a server that executes python, and then make HTTP requests to my server.
Unfortunately, I'm quite a junior developer and lack a lot of understanding regarding web dev, and my attempts to "dive in" have left me with more questions than answers. We have a deadline that is approximately 3 days from now, and the only part that remains is to set up a server that can execute a specific python script upon HTTP requests.
I think that the source of my confusion is a lack of understanding regarding how exactly a server works, and was hoping that the kind folks here at stack overflow could help me in:
1) better understanding what's going on "under the hood" on the server side after an HTTP request arrives (or better yet, how does an HTTP request even arrive at all?)
2) Explain to me like I'm 5 what I'll need to do to deploy my website - namely all the in-between steps that receive little attention from the other posts here at stack overflow.
Some example questions that run through my head are below:
What type of server will I need?
How will I know if it can run Python?
How does the server know that I want to execute a certain script, while upon a user entering a my website's homepage URL, land at the home screen?
I've also read up on "middle layers" such as 'CGI' - what does this accomplish?
Is setting up a server reinventing the wheel?
enter code here
Is there already a service out there that does what I'm looking for?
I've accomplished a similar project overnight with a Python web framework called Django, simply by following their official tutorial: https://docs.djangoproject.com/en/1.7/intro/tutorial01/
Django abstracts away all the web stuff for you and there's plenty of documentation on deploying it in various environments. With such deadlines I suggest you to just follow the tutorial above and eventually adapt the example to your use case testing it on Django's built-in web server, then follow a guide on deploying Django projects in your production environment.
I have a server with a database, the server will listen for http requests, and using JSONs for
data transferring.
Currently, what my server code(python) mainly do is read the JSON file, convert it to SQL and make some modifications to the database. And the function of the server, as I see, is only like a converter between JSON and SQL. Is this the right procedure that people usually do?
Then I come up with another idea, I can define a class for user information and every user's information in the database is an instance of that class. When I get the JSON file, first I put it into the instance, do some operation and then put it into the database. In my understanding, it adds a language layer between the http request and the database.
The question is, what do people usually do?
The answer is: people do usually that, what they need to do. The layer between database and client normally provides a higher level api, to make the request independent from the actual database. But how this higher level looks like depends on the application you have.
People usually make use of a Web framework, instead of implementing the basic machinery themselves as you are doing.
That is: Python i s a great language that easily allows one to translate "json into sql" with a small amount of code - and it is great for learning. If you are doing this for educational purposes, it is a nice project to continue fiddling with, and maybe you can have some nice ideas in this answer and in others.
But for "real world" usage, the apparent simple plan comes up with real world issues. Tens or even hundreds of them. How to proper separate html/css template from content from core logic, how to deal with many, many aspects of security, etc...
Them, the frameworks come into play: a web-framewrok project is a software project that had, over the years, and soemtimes hundreds of hours of work from several contributors, thought about, and addresses all of the issues a real web application can and will face.
So, it is ok if one want to to everything from scratch if he believes he can come up with a a framework taht has distinguished capabilities not available in any existing project. And it is ok to make small projects for learning purposes. It is not ok to try to come up with something from scratch for real server production, without having a deep knowledge of all the issues involved, and knowing well at least 3, 4 frameworks.
So, now, you've got the basic understanding of a way to get to a framework - it istime to learn some of the frameworks tehmselves. Try, for example, Bottle and Flask (microframeworks), and Django (a fully featured framework for web application development), maybe Tornado (an http server, but with enough of a web framework in it to be usable, and to be very instructive)- just reading the documentation on "how to get started" with these projects, to get to a "hello world" page will lead you to lots of concepts you probably had not thought about yet.
I know that with the SimpleHTTPServer I can make my directories accessible by web-browsers via Internet. So, I run just one line of the code and, as a result, another person working on another computer can use his/her browser to see content of my directories.
But I wander if I can make more complicated things. For example, somebody uses his/her browser to load my Python program with a set of parameter (example.py?x=2&y=2) and, as a result, he/she sees the HTML page generated by the Python program (not the Python program).
I also wander if I can process html form submitted to the SimpleHTTPServer.
While it is possible, you have to do pretty much everything yourself (parsing request parameters, handle routing, etc).
If you are not looking to get experience in creating web-frameworks, but just want to create a small site you should probably use a minimalistic framework instead.
Try Bottle, a simple single-file web framework: http://bottlepy.org
Maybe the VerseMatch project and related recipes over at ActiveState is something you would be interested in examining? It implements a small application using the standard library for dynamic running.
have you considered using CGIHTTPServer instead of SimpleHTTPServer? Then you can toss your scripts in cgi-bin and they'll execute. You have to include content-type header and whatnot but if you're looking for quick and dirty it's real convenient
As far as I know, for a new request coming from a webapp, you need to reload the page to process and respond to that request.
For example, if you want to show a comment on a post, you need to reload the page, process the comment, and then show it. What I want, however, is I want to be able to add comments (something like facebook, where the comment gets added and shown without having to reload the whole page, for example) without having to reload the web-page. Is it possible to do with only Django and Python with no Javascript/AJAX knowledge?
I have heard it's possible with AJAX (I don't know how), but I was wondering if it was possible to do with Django.
Thanks,
You want to do that with out any client side code (javascript and ajax are just examples) and with out reloading your page (or at least part of it)?
If that is your question, then the answer unfortunately is you can't. You need to either have client side code or reload your page.
Think about it, once the client get's the page it will not change unless
The client requests the same page from the server and the server returns and updated one
the page has some client side code (eg: javascript) that updates the page.
You definitely want to use AJAX. Which means the client will need to run some javascript code.
If you don't want to learn javascript you can always try something like pyjamas. You can check out an example of it's HttpRequest here
But I always feel that using straight javascript via a library (like jQuery) is easier to understand than trying to force one language into another one.
To do it right, ajax would be the way to go BUT in a limited sense you can achieve the same thing by using a iframe, iframe is like another page embedded inside main page, so instead of refreshing whole page you may just refresh the inner iframe page and that may give the same effect.
More about iframe patterns you can read at
http://ajaxpatterns.org/IFrame_Call
Maybe a few iFrames and some Comet/long-polling? Have the comment submission in an iFrame (so the whole page doesn't reload), and then show the result in the long-polled iFrame...
Having said that, it's a pretty bad design idea, and you probably don't want to be doing this. AJAX/JavaScript is pretty much the way to go for things like this.
I have heard it's possible with AJAX...but I was
wondering if it was possible to do
with Django.
There's no reason you can't use both - specifically, AJAX within a Django web application. Django provides your organization and framework needs (and a page that will respond to AJAX requests) and then use some JavaScript on the client side to make AJAX calls to your Django-backed page that will respond correctly.
I suggest you go find a basic jQuery tutorial which should explain enough basic JavaScript to get this working.
I'm just starting out with Python and have practiced so far in the IDLE interface. Now I'd like to configure Python with MAMP so I can start creating really basic webapps — using Python inside HTML, or well, vice-versa. (I'm assuming HTML is allowed in Python, just like PHP? If not, are there any modules/template engines for that?)
What modules do I need to install to run .py from my localhost? Googling a bit, it seems there're various methods — mod_python, FastCGI etc.. which one should I use and how to install it with MAMP Pro 1.8.2?
Many thanks
I think probably the easiest way for you to get started is to work with something like Django. It's a top-to-bottom web development stack which provides you with everything you need to develop and run a backend server. Things can be very simple in that world, no need to mess around with mod_python or FastCGI unless you really have the need.
It's also nice because it conforms to WSGI, which is a Python standard which allows you to plug together unrelated bits of reusable code to add specific functionality to your web app when needed (say for example on-the-fly gzip compression, or OpenID authentication). Once you have outgrown the default Django stack, or want to change something specific you can go down this road if you want.
Those are a few pointers to get you started. You could also look at other alternative frameworks such as TurboGears or paste if you wanted but Django is a great way to get something up and running quickly. Anyway, I'm sure you'll enjoy the experience: WSGI makes it a real joy knocking up web apps with the wealth of Python code you'll find on the web.
[edit: you may find it helpful to browse some of the may Django related questions here on stack-overflow if you run into problems]
You asked whether HTML is allowed within Python, which indicates that you still think too much in PHP terms about it. Contrary to PHP, Python was not designed to create dynamic web-pages. Instead, it was designed as a stand-alone, general-purpose programming language. Therefore you will not be able to put HTML into Python. There are some templating libraries which allow you to go the other way around, somewhat, but that's a completely different issue.
With things like Django or TurboGears or all the other web-frameworks, you essentially set up a small, stand-alone web-server (which comes bundled with the framework so you don't have to do anything), tell the server which function should handle what URL and then write those functions. In the simplest case, each URL you specify has its own function.
That 'handler function' (or 'view function' in Django terminology) receives a request object in which interesting info about the just-received request is contained. It then does whatever processing is required (a DB query for example). Finally, it produces some output, which is returned to the client. A typical way to get the output is to have some data passed to a template where it is rendered together with some HTML.
So, the HTML is separated in a template (in the typical case) and is not in the Python code.
About Python 3: I think you will find that the vast majority of all Python development going on in the world is still with Python 2.*. As others have pointed out here, Python 3 is just coming out, most of the good stuff is not available for it yet, and you shouldn't be bothered about that.
My advise: Grab yourself Python 2.6 and Django 1.1 and dive in. It's fun.
Django is definitely not the easiest way.
check out pylons. http://pylonshq.com/
also check sqlalchemy for sql related stuff. Very cool library.
On the other hand, you can always start with something very simple like mako for templating. http://www.makotemplates.org/