Develop Reference

Flask Custom Login and Template Rendering

I am new to learning Python for web development and have decided to go with Flask as my framework of choice as of now. I have chosen this primarily for its bare-bones approach on web development and I want to make as much of my web app custom and on my own as possible. I have made a very basic MVC framework in PHP and would like to make something like this in Python. I was researching some ways to interact with a database and add user login/register support and my original thoughts were that I wanted to do this all custom with my own methods and objects and what not. Similar to how I have done in PHP, so I can learn as much about developing my own back-end efficiently for long term production projects. In some research I found the basic objects in Flask such as Login Manager, Login-Form and Flask-Admin, etc. I don't like the idea of using these nicely packaged things that I have very little control over and have not dev'd custom.
Using that kind of stuff I also feel that I am not learning how all of that stuff works on the lowest level so I could not reproduce some of the benefits they are giving me later on in life when project circumstances change and maximum flexibility, customization, maintainability, and efficiency is needed. Obviously I am not in that position right now, but I DO know how to write this back end stuff in PHP and am just wondering if that means anything as far as managing sessions and Authentication on my own in Python/Flask, or if my thinking is totally out of ocontext and its not even close to managing the same stuff.

It is a really great idea to learn how authentication works at a low level -- it's particularly important as many people never learn this stuff, and it's quite interesting!
What I'd recommend you do is take a look at the official Flask tutorial (http://flask.pocoo.org/docs/0.10/tutorial/), as it covers a lot of this (working directly with sessions, etc.).
What I would not recommend, however, is using this sort of thing in production.
Using your own authentication code is almost never a good idea -- it's much better to rely on a well supported library that has been audited by other people for security issues.
In the Flask world you've got a couple choices:
Flask-Login: https://flask-login.readthedocs.org/en/latest/
Flask-Security: https://pythonhosted.org/Flask-Security/
Flask-Stormpath: http://flask-stormpath.readthedocs.org/en/latest/
Of those 3, I really like Flask-Stormpath -- but I'm super biased as I wrote it =)
Flask-Stormpath supports the widest array of customization / etc., and allows you to do whatever you want with it.
Hope that helps!

Flask official doc have some app examples. One of them is MiniTwit a micro Twitter clone. As it is a complete app, you could found much of what you're looking for. If you want to make something greater, try Full Stack Python Flask tutorial

Will learning Django translates well into other applications?

Does anyone have experience using Python in different variaty of applications?
A little background - I am a 3D artist in an animation studio. I do programming in PHP and use Zend framework for my personal project. Python has always been a language I wanted to learn because it can be used within many applications our studio is using (3D MAX, MAYA to name a few) My supervisor knew about my web background and wanted me to create a web base time line manager for the company. From the requirement I'm expecting quite a simple backend ... so it might be a good opportunity to finally learn Python. The bulk of the work will be on AJAX for the interactive front end.
So if I learn Python with web application and Django in mind, will that limit my Python skill from applying it to other applications?
a little curious about Django features as well. How well does the framework cover in terms of web application compare to Zend? Our application is pretty basic in the back end and I would love to know if Django will be able to cover them.
authenticate against Windows active directory
quick database update via AJAX interaction (drag and drop time line mostly)
Other basic stuff like discussion forum and directory browsing/file manager

So if I learn Python with web application and Django in mind, will that limit my Python skill from applying it to other applications?
No
authenticate against Windows active directory
Yes. You may need to customize an Authentication Backend.
quick database update via AJAX interaction (drag and drop time line mostly)
Django has nothing to do with Ajax. Use piston to create pleasant RESTful API that Ajax can use.
Other basic stuff like discussion forum and directory browsing/file manager
There are many, many canned applications for Django that you can plug in and integrate.

I love python as a language - but it's not the answer to everything. I know this is throwing mud in a python group, but python has one serious limitation - the rigid source code format.
While going through a django tutorial - I noticed that you cannot insert python source code into a template, and that this was presented as a 'feature' for separating programmers and designers.
I later realized that it's a limitation of django - and any other environment where python source code might get accidentally mangled. This also includes HTML WYSIWIG editors and database based 'manglers' (like Drupal).
In my opinion it's a very serious limitation with no easy cure - especially with the need to use other tools to manage the complexity of HTML / CSS / JavaScript.

I found Django a really good way to learn python. There's very little that's quirky, magical or un-pythonic in the framework. A bit of setup and you're away, writing standard python code.

What is a good reference for Server side development?

I am more interested in the design of the code (i.e functional design vs object oriented design). What are the best practices and what is the communities thoughts on this subject?
Not that it should matter, but I am working with Apache and Python technology stack.

If you are using Apache+Python, this sounds like you are using Python for dynamic web pages. In that case, I would strongly urge you to look into Django. There are also other Python web development environments, but Django is perhaps the most popular; and it has excellent documentation such as The Django Book. The Django Book describes best practices for setting up a robust web site: how to use multiple servers for redundancy, how to set up the database server, how to set up a cache to reduce the load on your database, etc.
Other than that tip, good Python server-side code would be just good Python code. There was a question asked recently about how to become a good Python developer, and I would suggest you read that: How do I get fluent in Python?

Python for web scripting

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/

Writing a website in Python

I'm pretty proficient in PHP, but want to try something new.
I'm also know a bit of Python, enough to do the basics of the basics, but haven't used in a web design type situation.
I've just written this, which works:
#!/usr/bin/python
def main():
print "Content-type: text/html"
print
print "<html><head>"
print "<title>Hello World from Python</title>"
print "</head><body>"
print "Hello World!"
print "</body></html>"
if __name__ == "__main__":
main()
Thing is, that this seems pretty cumbersome. Without using something huge like django, what's the best way to write scripts that can process get and post?

Your question was about basic CGI scripting, looking at your example, but it seems like everyone has chosen to answer it with "use my favorite framework". Let's try a different approach.
If you're looking for a direct replacement for what you wrote above (ie. CGI scripting), then you're probably looking for the cgi module. It's a part of the Python standard library. Complimentary functionality is available in urllib and urllib2. You might also be interested in BaseHTTPServer and SimpleHTTPServer, also part of the standard library.
Getting into more interesting territory, wsgiref gives you the basics of a WSGI interface, at which point you probably want to start thinking about more "frameworky" (is that a word?) things like web.py, Django, Pylons, CherryPy, etc, as others have mentioned.

As far as full frameworks go I believe Django is relatively small.
If you really want lightweight, though, check out web.py, CherryPy, Pylons and web2py.
I think the crowd favorite from the above is Pylons, but I am a Django man so I can't say much else.
For more on lightweight Python frameworks, check out this question.

There are a couple of web frameworks available in python, that will relieve you from most of the work
Django
Pylons (and the new TurboGears, based on it).
Web2py
CherryPy (and the old TurboGears, based on it)
I do not feel Django as "big" as you say; however, I think that Pylons and CherryPy may be a better answer to your question. CherryPy seems simpler,. but seems also a bit "passé", while Pylons is under active development.
For Pylons, there is also an interesting Pylons book, available online.

In Python, the way to produce a website is to use a framework. Most of the popular (and actively maintained/supported) frameworks have already been mentioned.
In general, I do not view Djano or Turbogears as "huge", I view them as "complete." Each will let you build a database backed, dynamic website. The preference for one over the other is more about style than it is about features.
Zope on the other hand, does feel "big". Zope is also "enterprise" class in terms of the features that are included out of the box. One very nice thing is that you can use the ZODB (Zope Object Database) without using the rest of Zope.
It would certainly help if we knew what kinds of websites you were interested in developing, as that might help to narrow the suggestions.

In web2py the previous code would be
in controller default.py:
def main():
return dict(message="Hello World")
in view default/main.html:
<html><head>
<title>Hello World from Python</title>
</head><body>
{{=message}}
</body></html>
nothing else, no installation, no configuration, you can edit the two files above directly on the web via the admin interface. web2py is based on wsgi but works also with cgi, mod_python, mod_proxy and fastcgi if mod_wsgi is not available.

I really love django and it doesn't seem to me that is huge. It is very powerful but not huge.
If you want to start playing with http and python, the simplest thing is the BaseHttpServer provided in the standard library. see http://docs.python.org/library/basehttpserver.html for details

I agree with Paolo - Django is pretty small and the way to go - but if you are not down with that I would add to TurboGears to the list

If you are looking for a framework take a look at this list: Python Web Frameworks
If you need small script(-s) or one time job script, might be plain CGI module is going to be enough - CGI Scripts and cgi module itself.
I would recommend you to stick to some framework if you want to create something more then static pages and simple forms. Django is I believe most popular and most supported.

What is "huge" is a matter of taste, but Django is a "full stack" framework, that includes everything from an ORM, to templates to well, loads of things. So it's not small (although smaller than Grok and Zope3, other full-stack python web frameworks).
But there are also plenty of really small and minimalistic web frameworks, that do nothing than provide a framework for the web part. Many have been mentioned above. To the list I must add BFG and Bobo. Both utterly minimal, but still useful and flexible.
http://bfg.repoze.org/
http://bobo.digicool.com/