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Python web frameworks vs Java web frameworks (how is web development in Python done?)

I am thinking in starting a personal pet web project to experiment with different things and extend my knowledge.
I use Java a lot at work (for web applications :D) and was thinking in making my own in Python since I kinda like this language but never passed the simple scripts stages.
I want to step up a gear regarding Python (using 2.6.5) and don't know what to expect or what framework to choose from: Django, Pylons, web2py etc.
I also don't know how much these frameworks will offer me and how much will I have to write from scratch.
I could use a comparison with Java if somebody can provide me with. I'm thinking at filter functionalities such as sitemesh, custom tags like JSTL; In Python, can I write clean pages of HTML with tags in them or write a lot of print statements (something like servlets did in Java etc?
I don't know exactly how to phrase this question.
I actually need a presentation of how web development is performed in Python, at what level, and what the web frameworks bring to the table.
Can you share from your experience?
TIA!

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Python web frameworks run the full gamut of capabilities/facilities, all the way from shims around WSGI such as Bottle and Flask, all the way to full frameworks such as Django and TurboGears, and even "megaframeworks" such as Zope. Each does things slightly differently, but there will be some familiarity from one to the next.

It may sound strange, but there's no need to know "how web development is performed in Python" to start doing it.
In fact, working with language/framework/etc is a single most reliable way to get understanding of it. You won't gain a lot from one-page summaries.
Also, comparing it with Java isn't likely to help. There's no point in doing "Java-style development in Python". If you want to benefit, you'll need to clear your mind and do everything "Python-way".
As to what Python framework to choose, Django seems like like a good starting point. It's very popular, which means you won't be left without tutorials/documentation/help.
PS Short version: just do it.

Python web frameworks do it in a similar way as some Java-based frameworks. I can speak for Django here.
A good comparison could be Play! vs. Django. Both of them foster using an MVC architecture (or MTV = models, templates, views) and already provide you with a lot of things like CRUD operations in admin pages, ORM, authentication, URL configurations, a template language and much more.
Other Java-based frameworks might differ a lot, and I can't give you a general answer. Depending on the choice, there are only few differences. You can simply choose the language and framework you like the most. I'd recommend to go through some tutorials (Django tutorial, Play! framework tutorial for instance) and look which one works best for your needs.

Java Backend and Rails Frontend

I have a startup considering building a Java backend and a Rails frontend. The Java backend will take care of creating a caching layer for the database and offer other additional services. The Rails frontend will mostly be for creating the webapp and monitoring tools.
What startups/companies out there are using this kind of setup? What are some gotchas in terms of development speed, deployment, scalability, and integration?
(What would be helpful for me is personal experience or informal case studies. I'd like to de-priorities answers addressing alternatives like Grails or JRuby unless it turns out to be a big part of the equation)
Thanks!

I've never done any rails development but here are my thoughts. Why not just use Grails? I've done a fair amount of Grails development and it works well for rapid prototyping. It also offers all the power of Java, Spring, and Hibernate. Instead of dealing with communication between two different technologies you could take advantage of the fact that Grails uses Spring and Hibernate under the covers to deal with caching as well as any other requirements these technologies support. If you have Java developers Grails should not be to hard to pick up. The grails plugin story is decent. All of them are stored in a central place and are easy to obtain but quality differs depending on the plugin author. You also have to remember that since Grails uses Groovy which is syntactically similar to Java and runs on the JVM it is very easy to use existing java code including the multitude of available Java libraries. I don't know this for certain but I assume there are a lot more libraries out there for use with Java and there for with Grails then are available for the Ruby language and Rails. I can't make a resource usage call for you but my question would be how many people do you have with experience designing Rails systems that use Java on the back end with all the gotchas that will go along with that? You may find that you have no one who is proficient at debugging when something goes wrong in communication between the two technologies.

I have used similar pair for one of my projects, but instead of RoR I used Python. I don't think there's large difference.
In general, there's nothing specific in this kind of programming. Two most important things you must care about:
good modularity;
well thought-out protocol between RoR and Java.
First is about exact functionality decomposition between parts of the system. We've got some troubles because of not understanding what part of a job must be done by Java, and what part by Python. In general, you must tie together all functions that are close to each other, and thing that are far must be connected in a very few places. I guess you know rules of good modularity, but in case of composing different languages this must be thought-out much more carefully. You can also be interested in creating several distinct Java services (e.g. one for database caching and another one for all the rest) to be able freely combine them or even use in other projects later.
Second is about communication between your parts. I can see two ways to communicate: through database and through pure network protocol. The former need some network communication anyway, so we used pure network protocol, without any other way to connect parts.
We had experimented a lot with SOAP, but it gave hundreds of errors: this protocol is quite ok to connect services written in one language (i.d. Java to Java), but terrible for connecting services in different languages - automatic tools for generating WSDLs gave different results for Java and Python, and manual creating of scheme was hard and labor-intensive.
So we used to REST. It uses all the features of HTTP protocol such as all four main HTTP methods (POST, GET, PUT, DELETE), error codes and many other things, so it covers almost everything you may want. The only restriction with REST is that it can't hold state, so you may need to implement your own sessions mechanism.
If you're not very comfortable with REST and seek some real example, see Facebook Graph API and for implementing REST services in Java you can use Restlets.

Perhaps I'm stating the obvious here, but the biggest gotcha here is the actual fact you're combining two technologies. Not only will development be slower - Rails and all Java frameworks are expecting to have a full Ruby/Java application - but for the other issues you mention (deployment, scalability, integration), the existing tools and solutions will not work, or at least not very well.
If you have a compelling reason to combine the two, go ahead but expect to spend more time on these issues than with a single technology solution. If you don't, pick either Rails or Java.

I would strongly urge you to consider having the frontend and backend in the same JVM for performance reasons.
For Rails, JRuby can run Rails, and you can have it in a Java EE container providing fast communication between components.
Having multiple architechtures which do not run in the same process requires you to do network based communication which takes much, much longer than just passing a reference to an object (I do not expect you to want to use shared memory).

Twitter.com is supposedly using a Java backend, and Rails for their web interface. Here are some resources:
http://www.radicalbehavior.com/5-question-interview-with-twitter-developer-alex-payne/
http://blog.adsdevshop.com/2008/05/02/twitter-is-not-abandoning-rails/
http://twitter.com/#!/ev/status/801530348
More specifically, they use Scala on the backend (which compiles to Java byte code):
http://www.artima.com/scalazine/articles/twitter_on_scala.html
I don't think there is anything wrong with this approach. However, you will be supporting two different platforms/VMs. I have seen this kind of situtation result in a sort of fracturing of expertise within an organization. And you end up paying to a lot to have two sets of expertise in house.
If the problem of segmenting expertise concerns you, I would suggest running JRuby of Rails. It is very mature now - and runs better than Rails on Ruby 1.8.x.

We have used Ruby on Rails for front-end and Core-Java SOAP Api for backend. It worked very well.
The main issue is not with performance but with the people. It is very difficult to hire expert people in Ruby on Rails for everything, instead you hire few or you can easily mould to just learn Rails UI.
As startup point of view, it is best strategy. So many believe ROR is best for startups... but very few knew it because in most of MNC's we use Java, so there is pressure to learn Rails and Code, or hire very few ROR developers. So instead you can use ROR for frontend (only few people do that, or it is easy to learn) and use experienced Java developers for DB updates and business logic.

I want to make a "Web 2.0" application without using JavaScript directly

I'm a full time Java developer of around 4 years, professionally. I'm a GWT fanatic. I love Java. Here's the problem: In my free time I often fall victim to the verbosity of my favorite tools for doing "heavy" development. I also often fall into the trap of obsessively engineering my software. I'll end up with the most beautiful unfinished implementation, ever.
So, here's what I normally work with.
GWT - I use this for dynamic UI and web layout. I love the ease of re-use and it has taught me to absolutely hate javascript. I really can't even bring myself to do much HTML/JS anymore.
Hibernate - POJO to Database, easy-peasy. What i really need from this other than the mapping is that it allows me to have an application that works across multiple databases.
Spring - Mostly security. I've written my own custom LDAP bits for a project.
XML - I've used dom4j and other implementations, including xstreamer. I'd like to use JiBX for XML transport. The problem with this is that I need XML messages that conform to a specific standard rather than being autogenerated. Object->XML->Object are also common enough that it can be a performance bottleneck with large messages (250KB+).
I tried Lombok for a little while and liked it but had occasional issues with it and then I blew up a partition and lost all that work. I don't really feel like doing the same thing again (half the fun was in learning how to do it, now that I know... meh). This taught me why other people want to reduce the explicit code and replace it with an implicit system.
I've been looking into Grails but that runs me into the JavaScript problem (you know, that I don't like it) pretty quickly. I could use GWT with Grails on the back end but I get back into the problem of getting deep in the weeds with GWT. It has also occurred to me that there might be a way to have Grails tags in GSP that are made up of GWT widgets. I'm not really sure how I feel about that.
Another problem I have with Grails is that validation logic before form submission is separated from validation constraints after submission. I don't see how they can be unified (yet) to produce "pretty" front-end validation. I went out of my way to start a JSR-303 compliant validation project for GWT to help solve some of this problem for GWT and really liked the results. It isn't finished but I still find it useful.
So, help me find a better way!
TL;DR - I want to have a Database (and Database-Independent) to GUI solution that allows for dynamic web programming all in one language. Failing that, as close to one language as possible.
TL;DR is TL;DR - I hate JavaScript now, help.
EDIT: I know that it is techincally impossible to do "Web 2.0" development without JavaScript. I'm just trying to not be the guy who has to write it. (Getting a tool such as GWT to do it for me from a language I do like, for example.)

Just learn JavaScript.
Resistance is Futile
...and you will be assimilated.
PD: I'm an ex JavaScript enemy. Now it's my favourite language.

You can certainly develop an entire Web 2.0 project without coding Javascript using GWT (we have), but at the end of the day you still have to know HTML/CSS & Javascript.
This might sound like a stupid statement, but it's not once you consider that GWT is not a perfect abstraction, nor is it designed to be. It wasn't written in Java so that you didn't have to ever code in Javascript again, instead they did it because Java has better IDE's, is statically typed and makes maintenance a hell of a lot easier.
So yes, by all means go with GWT (and check out the new OOPHM, because it's AWESOME) but don't forget that you'll always need an understanding of the underlying frameworks of the web, if you want to develop for the web.

Have you heard of Echo?
It doesn't provide the database part of the problem, but it would work well with any database that you can work well with.
Echo is a platform for building
web-based applications that approach
the capabilities of rich clients. The
applications are developed using a
component-oriented and event-driven
API, eliminating the need to deal with
the "page-based" nature of browsers.
To the developer, Echo works just like
a user interface toolkit.
The latest iteration, Echo3, features
the ability to write applications in
either server-side Java or client-side
JavaScript. Server-side applications
run in any Java Servlet Container and
do not require developer knowledge of
HTML, HTTP, or JavaScript.

You might want to take a look at some of the AJAX powered JSF libraries. IceFaces and RichFaces are both solid.

Been there, done that. I was a GWT developer for 3 years... I started using it in v1.1! GWT is fantastic, and works really well for small applications. But the development comes to a crawl once you it a moderate application size, even if you divide your application in sub-modules.
It is also quite ironic that a UI framework has such limited UI creation tools. :)
Personally I bit the bullet and learned javascript. It isn't as bad as I thought. Especially with jQuery. :)
Obviously there is no perfect framework. But just the fact that GWT has been out for 3.5 years now, and it still largerly ignored in the Java world should tell you something. Since you're doing this on your free time, I would recommend learning the most popular framework: Struts. You'll see its limitation, and also why it is so popular. Of course, you'll need jQuery for that 2.0 functionalities. :)

Take a look at JRapid, a rapid development platform for Java developers. It generates very powerful Ajax enabled UI without the need of coding.

Not sure if you would like this , but have you heard about Haxe?
You might not like it but its AIO (all in one) solution (sort of).

I can understand your dislike of JavaScript and it certainly has its problems but I think your fighting nature at this point.
Web 2.0 is strongly based on JavaScript for a good reason as it provides the ability to perform tasks on the client machine without requiring page loads.
I'm sure there are alternatives but if you want the look and feel of Web 2.0, you will end up doing a lot more work with little reward. JavaScript is the accepted and functional tool for the job.

I'd say stick with GWT and just drink more of the Koolaid. It's a completely awesome development model that seems to be lost on those who haven't tried it.
If you want to improve your GWT experience, jump to the bleeding edge (I work off trunk, it's quite stable) and use the other Google originated projects like GIN, gwt-incubator and Guice. Especially watch Ray Ryan's GWT best-practices Google I/O talk: http://www.youtube.com/watch?v=PDuhR18-EdM
As for the "framework" part: forget 'em. Just use normal servlets and let GWT take care of the RPC for you. Servlets are a pain when you have to deal with JSP and you're own AJAX calls, but when they're only implementing asynchronous app logic, it's not that bad at all. Guice Servlet makes it all quite easy. You can still use a JVM hosted language to write your servlets if you want.
GWT has an incredible advantage over other JavaScript frameworks in that the layer of abstraction it provides allows for major future advances without any changes to your code. If the GWT compiler and browser detection scripts can take advantage of new browser features then you benefit from a simple recompile.
The big annoyance I see in your requirements in XML... hopefully that's just for integration with a 3rd party service and your client-server communication can just be GWT-RPC.

I don't use javascript or ajax, in medium-large application they create a lot of problem with compatibility, because moving some part of code inside client, create security breaches and problem with different browser.
I use only HTML(5) and CSS2/CSS3, and I have a lot successes.
I use this 2 ways:
using "puzzle-techinque". Write a lot of small and simple template (or tiles) to create the big page. I use only JSTL and Spring tag, with Rich/Prime/Ice-faces I encountered a lot of problem with rendering, page building and flow controller, so I discarded them.
using my custom library to parse HTML pages. I create template with my custom grammar, put inside the parser and write on output stream. This is the best way.
If you say me your preferred language and context, I can help you to perform JS-free.

How to rapidly build a Web Application?

To build a Web Application, what kind of open source web application frameworks / technologies are currently present that would be:
Faster to learn.
Ease of use.
Have widgets for rapid development(From a GUI perspective).
Database integration.
I would want this web app to communicate to a Java client.
I am not bound to Java on the server side and free to try out any good rapid application framework.
To summarize, I haven't done much work for the server side hence am not conversant with the tools and technologies for the same.
What would you suggest?
Any and every input would be welcome!...

There is no single "right" answer to this question. As a Java programmer of some 10+ years when asked this question my usual answer is... PHP. There are several reasons for this:
Low resource usage (Apache, nginx);
Cheaper hosting;
Really low barrier to entry;
It's really Web-oriented rather than being general purpose that can be used for Web (like Java);
The fact that PHP scripts aren't persistent (like Java servlets are) between requests makes them much more forgiving and less likely to cause memory leaks and other problems;
No deployment step (like Python, Perl, etc). I'd say this is about the best thing about dynamic scripted languages. Just save the file and click reload on your browser;
PHP might be inconsistent in syntax and several other things but it's also mature and used by some really large sites on the Web (eg Facebook, Yahoo, Flickr, Wikipedia);
PHP is by far the most popular Web development language.
Widgets can be done by any manner of Javascript frameworks like YUI, ExtJS, SmartClient, jQuery UI, etc;
PHP fits well with MySQL.
That being said, a lot of these apply to other languages too (eg Python/Django).
I don't think you necessarily need a framework for PHP but if you do I'd look at one or more of:
Kohana: it's like a more modern version of the more popular CodeIgniter;
Zend Framework: it's modular so you can use as much or as little of it as you like;
Smarty: it's a powerful templating system.

Django has a few notable 'rapid' items including automatically generated administrative interface, bundled ORM (lowers dev time by not having to write SQL and some other code), and a large community with several re-usable apps.
Where Django (or Ruby on Rails or any other MVC framework for that matter) isn't going to be rapid is the learning curve when you first come to developing on them. Django (and RoR) have quite a bit of seperation-of-concerns and if you're not used to that sort of environment, it takes a while to learn the framework. If you're using an ORM that's something to get used to as well, and then of course for any framework you go with there's the API to learn as well.
PHP on the other hand is a little more intuitive in terms of where you put the code and how pages make up your web app. It'll basically let you slap code wherever you want so in the beginning it will probably be faster. In the end it will be quicker but your final product will be sloppier and probably require re-factoring later on.
This comes down to a question of what's the use of the framework. If it's for a hobby site, just go with what's easy (php), otherwise you might want to consider a well-supported MVC framework.
As others have pointed out, jquery is probably the pick for pre-made GUI widgets.
Edit -- And apparently now Django (as of 1.1) has a very awesome set of unit testing tools it comes bundled with. Things like an extended TestCase specifically for Django, a test client (you can do test page request w/o an actual client or server), a tool to give you a % of test coverage you have of the project, and a bunch of other neat stuff.

You've already tagged your question with "java", "php", "python", and "ruby-on-rails", so researching and learning more about those tools would probably help to answer your question.
However, I believe that rapidly building an application is almost never actually the correct goal. Normally, what you want to do is build an application that can be rapidly maintained -- that is, maintained with the lowest possible overall development cost over time.

I would say part of the learning curve will go into understanding concepts. I have been learning about web-apps for some months now, and with my improved understanding of concepts right now, most frameworks show very much similarities. Here are my results so far:
PHP: Great to learn about concepts for doing forms, http-post-requests, http-get-requests. easy interaction with database layer, and it is possible to obtain a working basic application in couple of hours. Almost no hassle with build-systems and web-server configuration.
Ruby-on-Rails: Great to learn about REST and more complicated CRUD applications. Great to learn about the complexity behind MVC and especially simple and powerful interaction with the database layer by using ActiveRecord. Introduction of meta-programming (code-that-writes-code, code-scaffolding) is great. Nice opportunities for free cloud-deployment, e.g. heroku.com and there is a very active community
Java: Powerful interaction with web-server possible (Tomcat, JBoss, ...) MVC is rather complicated here, and in general many configuration-steps necessary (build systems, ORM layer, ...) Grails is a great simplifaction and introduces meta-programming for Java. Jboss Seam introduces REST for Java (but have not looked into this yet)

There are tons, which ones are "good" depend on what you need.
There's Ruby on Rails, which is pretty handy.
For python there's django.
For PHP (I spend a lot of time dealing with PHP), you can look at:
symfony
cakePHP
Solar
Zend Framework
Which are all good in certain situations, and annoying in others.

Speaking only in terms of speed of development, Ruby on Rails is the fastest one out there.

I would vote for Grails.

You can build an runnable Java Web application within 5 to 10 minutes by using the following online Java web application generator:
http://www.webappexpress.net

Java for the web

I posted this question: https://stackoverflow.com/questions/418597/java-and-net-for-php-programmer and the answers I was given didn't really help me out.
I read a few of the tutorials at sun.
The basic syntax I understand. The thing I don't understand and really need to (because I think my company is going to tell me start working with this) is to learn how to work with java for the web. I am a php programmer and I did some asp.net c# a few months ago. I am really not understanding how to work with java on the web.
I installed netbeans.
When I start a web project I also get asked what frameworks I want.
I don't know any java frameworks (I do know about spring but never really worked with it).
Is there no simple tutorial on how to do some java for the web??? I never had these much problems when I was first introduced to php :(
Someone help me out, or at least point me in a good direction.

You may find this question helpful.
All you really need to know is HTML, Java, and JSPs.
Creating dynamic content is very easy using JSPs and Java. You also need a webserver like Tomcat or Glass Fish.
As far as the back end Java code goes, there is no difference between that and a desktop application. The only thing that you are changing is the user interface. One of the biggest challenges with switching to a web interface is the fact that it is stateless by design.

The frameworks make web programming easier, they're not required. You can write web applications using plain old servlets and JSPs (with a web application container like Tomcat or JBoss) or even do all the HTTP I/O yourself (obviously that's pointless with Tomcat, etc, around).
A framework like Spring with Hibernate, etc, is similar to frameworks in PHP like CakePHP, they make development easier, they enforce sensible patterns (MVC) upon the programmer, the abstract code that is always going to be done the same way for this type of application. Yes, they limit your choices and abilities, and restrict the actions you can take, to varying degrees. Some are far more heavyweight than others. But there's a lot of choice in the Java world which is a strength, but you just have to spend time evaluating them, and picking one based upon your capabilities.
Take struts and tiles. You can simply use Struts as an MVC system and avoid all of the utility JSP tags it provides. It would take you a short time to rewrite the functionality you end up using yourself, but that's time you don't have, and then there's debugging, and specific domain knowledge and experience that you can't account for.

Are you familiar with MVC? There are multiple frameworks in Java that implement it. Struts is one of the more popular. It may help to start using Struts and work through a tutorial.
This tutorial is a good one that also will introduce you to spring.
This tutorial deals with struts in netbeans

By technical side, you can start downloading Tomcat and code the exercises and documentation.
By "architectural" sie, you code in Java the business logic, that is all the components that take the parameter by communication client-server (request), manipulate this and use this for create the result.
this result is give to communication server-client (response) and it appear, with presentation layer (JSP, etc) in the web page.
The explication is very preciseless and not very "orthodoxe", I know.
It's matter that you understand.

The programming model that is (in most cases) used when writing a Java web application is actually a subset of J2EE. Not a rocket science, but there's a need to know at least bits of it.
Get yourself familiar with concept of J2EE Web Container, J2EE Web application, it's descriptor (web.xml), Servlets (which are, in fact the basic "building stones" of any J2EE webapp) and, of course, JSPs.
Sun has many nice tutorials on their's web pages. Googling any of the above terms with "site:sun.com" usually brings good results (e.g. this one about the concept of Servlets: http://java.sun.com/products/servlet/articles/tutorial/ ).
I'd also forget about web frameworks first, and start with the J2EE stuff, then MVC as a design pattern. After that, go into the web frameworks. Use of a framework is usually of a great help, but even when using one, you still need to know the basics.

Since you're using NetBeans, start with the tuturials they have on their site.
http://www.netbeans.org/kb/docs/web/quickstart-webapps.html
Go through the simple tutorials on the site before you start going into the details on any frameworks.
Java webapps are pretty simple. You have your Java classes (.java) that handle your business logic and your .jsp files that handle the presentation. Try and keep them seperate. You also want to familiarize yourself with the JSTL tags and el (expression language) syntax