Develop Reference

Code completion similar to intelliJ for python

I recently started working with Java and I really like to auto-correction / completion features in IntelliJ.
Does it exist something similar and as powerful for python?

I presume you are using JetBrains IDE so you could try out their PyCharm for python. It's from the same company so I presume that PyCharm's autocomplete features are on par with that of IntelliJ
As I never used IntelliJ, the recommendations below are based on the autocomplete features of PyCharm.
I was using tabnine on vs code and it does support many ide's however I stopped using it now since it is using too much resources on my laptop and I feel that auto complete is kind of distracting (but that is just my opinion). You could also try Github's Copilot, my friend uses it but for reasons mentioned earlier, I didn't try it. These two however, may not be the autocompletes you are looking for as they can basically write your code for you.

Dig into variables while debugging

I am currently debugging code using Python. I have not been using Python for a while. I put some breakpoints on a variable which is an integer. Let's say this variable is X = 10. How can I:
see what is in the variable? (I can highlight and a yellow case appears but if there are a lot of information it is not practical to display like this)
do some manipulation of the variable, for example I would like to do X+2 and get the result?

As noted in the comments, there are many possible IDEs you can use with Python. The original question was specifically about Eclipse and so my answer focuses on a solution using that IDE. Other solutions are possible if you prefer a different environment...
First off, you need to sort out which plug-in you use for eclipse. You have a few options as you can see on the python wiki. It looks like PyDev is more popular, but you could pick others.
Assuming you go for PyDev, you can use the watch facility as described here to evaluate any expression. Alternatively you can use the console debugger to evaluate code directly in the debugger.
EDIT: As per the comments, you can also open the Expressions window using Window > Show View > Other > Debug > Expressions. This is the same window as used for the watch facility and the contents can be edited directly.

I'm sure everyone has their own opinion, but I find the python tools for Eclipse quite complex. If you aren't tied to an Eclipse IDE, try PyCharm. It has very good tools for doing exactly what you want, and many tutorial videos. This video shows you how to do exactly what you have requested: https://www.youtube.com/watch?v=QJtWxm12Eo0

I don't think you can do this purely in Eclipse, not without extensive plugins. However, there are some very good python debugging tools out there.
If you're willing to get your hands dirty, the builtin python debugger pdb does everything you want and more. Import pdb, pdb.set_trace() where you want to break, and you step into an interactive debugger that's very familiar if you've used gdb before.
If you want to use something more IDE focused, I recommend Immunity Debugger. It's really rather good, and has a lot of documentation. This might be a little more than you're looking for though.

Try opensource, free VS Code (with Python plugin). It has a slick intellisense feature and you can watch, inspect the variables, debug them. The editor is node.js based and can work in every platform. Eclipse is overkill for python development IMHO.

ipdb is a handy tool for python debugging:
ipdb exports functions to access the IPython debugger, which features tab completion, syntax highlighting, better tracebacks, better introspection with the same interface as the pdb module.
To install ipdb, simply run pip install ipdb --user in your shell.
To set breakpoint, add import ipdb; ipdb.set_trace() before the line where you want to jump into the debugger. E.g.:
import ipdb; ipdb.set_trace()
X=10
Once you run your program python myfunc.py, an IPython-like interactive shell will be triggered and you can run python commands in it. E.g.:
ipdb> p X
10
ipdb> X+2
12
Here is a simple tutorial: An Introduction to Python Debugging

In Python, how do I debug with an interactive command line (and visual breakpoints?)

I've recently moved from Matlab to Python. Python is a much better language (from the point of view of a computer scientist), but Python IDEs all seem to lack one important thing:
A proper interactive debugger.
I'm looking for:
The ability to set breakpoints graphically by clicking next to a line of code in the editor.
The ability to run ANY CODE while stopped in the debugger, including calling functions from my code, showing new windows, playing audio, etc.
When an error occurs, the debugger should automatically open an interactive console at the error line.
Once done with the interactive console, you can resume normal execution.
Matlab has all these features and they work incredibly well, but I can't find them anywhere in Python tools.
I've tried:
PyCharm: the interactive console is clunky, often fails to appear, and crashes all the time (I've tried several different versions and OSs).
IPython: can't set breakpoints -Launching a Python console programatically: you have to stop your code, insert an extra line of code, and run again from the beginning to do this. Plus, you can't access functions already imported without re-importing them.
Being able to debug and fix problems THE FIRST TIME THEY APPEAR is very important to me, as I work in programs that often take dozens of minutes to re-run (computational neuroscience).
CONCLUSION: there is NO way to do all of these in Python at the moment. Let us hope that PyLab development accelerates.

At the top of your code, write
import pdb
And within your code, use the following statement wherever you want to debug.
pdb.set_trace()
You will have an interactive shell thus, whenever the set_trace() statement is met.
You can then use step(s), next(n), continue(c) and so on to check the execution flow, and print values of variables like print var
For more details on pdb, refer here

There are many Python IDEs. That was a topic here: What IDE to use for Python?
"The ability to set breakpoints graphically by clicking next to a line of code in the editor."
PyDev has this. Double-click in the gray margin bar.
"The ability to run ANY CODE while stopped in the debugger, including calling functions from my code, showing new windows, playing audio, etc."
PyDev has this. It's not the only one. PyScripter's stated features seem to include this.
"When an error occurs, the debugger should automatically open an interactive console at the error line."
PyDev does this. (I think. Or at worst do you need to double-click on the console message that states the error's location in the code?)
"Once done with the interactive console, you can resume normal execution."
PyDev has this. It's called "resume". It's what the green "play" triangle in a toolbar does. Some other software calls this feature "continue".

I've been searching for the same, but unfortunately Python IDEs are not as well-featured as Matlab's at this point. For scientific programming, you will also want graphics/plotting to run in an entirely different thread, so IPython integration is essential. As far as I can tell, the Matlab IDE feature to change the workspace from the debugger, which then affects code running subsequently, is quite unique. Each of the features exist in some IDE, but none exist in all:
Spyder has good integration with scientific tools, but its debugging is limited to the built-in pdb, which lacks the requirement to execute any code and have this code affect the namespace after continuing.
PyDev and PyCharm, and quite a few others, have decent debugging features, but I don't think it has good integration with scientific tools. That means, if you plot, you lose access to your prompt. Not good.
As far as I've experienced, the closest comes Wing IDE. It is a propietry product, but if you're making the transition from Matlab 89$/year for non-commercial-use should be acceptable (you can evaluate it first). But for me, I've ultimately settled to alter my workflow, and not using any sophisticated IDE at all. When I looked was some years ago, so perhaps the situation has improved.
You might also be interested in this article from April 2013, Evaluating IDEs for Scientific Python. It doesn't really reach a conclusion either.

Seeing as you are comming from Matlab, I would suggest you give a look at
Python(x,y)
The page decribes it as follows:
Python(x,y) is a free scientific and engineering development software for numerical computations, data analysis and data visualization based on Python programming language, Qt graphical user interfaces and Spyder interactive scientific development environment.
It will not cater to all your wishes, but it certainly made me feel comfortable when I started out with Python, coming from Matlab.
Hope it helps

You can do all this in the iPython Notebook. Use the magic command %pdb to stop on error.

If using the command line,
alias ipythondebug='ipython --InteractiveShell.pdb true'
in your ~/.profile will give you debug on error like Matlab. This of course requires ipython installed.
Not sure about the resuming part.
You can also edit the ipython config file if you want the debug on error to be permanent. See
https://ipython.readthedocs.io/en/stable/interactive/magics.html#magic-pdb

Experienced Python programmers (ESPECIALLY former php programmers) : How do I debug python?

In PHP, it was extremely easy to start hacking away and figuring out what was going on on a page. Just throw in a bunch of echos and print_r's and that was about it. It appears that this technique is not working for me in python. I am getting practice by hacking around in a python photo upload module, and when a photo is uploaded, it creates 3 different size photos. I found the code that does this, but I want to see the state at that particular moment. I tried doing a "print" on the size variable, but it did not show up in my browser.
I guess a more straightforward question would be, is it "pythonic" do debug using the browser ( equivalent to echo's and print_r's in php ), or is this what the python console is for? Thanks!

Use the logging module rather than printing stuff to stdout.
Using the interpreter in interactive mode is a great way to try out code, and pdb is very useful for real debugging.

It's "pythonic" to do debugging using the pdb module.
But really, if you're just "hacking around", then I suggest messing around with an interactive interpreter interface, especially one that supports autocompletion (Python itself comes with IDLE right out of the box).

You need to learn how to use a debugger ;) Hacking with prints is cool for simple php, but you can save a lot of time in higher languages with a debugger.
As mentioned, PDP is a place to start http://docs.python.org/library/pdb.html

As others have mentioned PDB, I'll take the opportunity to sing the praises of Eclipse using the pydev plugin, which is absolutely fantastic. IDLE is also well worth a go. Both of these IDEs allow you to step through code, inspect variables, auto-complete, etc. etc.
http://pydev.org/
Download Eclipse then use the Software Updates menu to add in PyDev.
http://pydev.org/updates

PyCharm from JetBrains is as good as all their other products. It has an integrated debugger and lots more.

New to Python. Need info on the environment for it

I'm a complete newbie to Python. I've worked on PHP/JavaScript earlier but starting today I'm moving onto Python. I have no idea about the environment needed for it. I could use some suggestions on it for me to get started.

Under Unix, Emacs is a good choice, to which I always come back, because it is convenient to have a single editor for everything, and because it's open source.
What is best for you depends on your past experience with IDEs. I'd say: stick with what you've been using, or take this opportunity to try an even better IDE.
Note: Python comes with Idle, which is a very simple (if limited) IDE.

Be sure to check out IPython. It's an enhanced interactive python shell with a bunch of useful features such as Tab-Completion using introspection (eg, type "my_object." to see a list of its attributes and methods), logging your interactive session to an executable python-file, defining macros, etc. The documentation page has a link to the tutorial as well as screencasts showing it in action.

On my mac/Linux machines, python came pre-installed. On windows I use both jython under the eclipse IDE and ActivePython with their IDE/eclipse.   With eclipse you'll want PyDev.

It all depends on what you are looking for and what you are already using.
For instance, if you are using a more 'simple' editor at the moment: as long as it's got Python syntax you've got the basics.
If you are used to e.g. Eclipse you can just continue to use that, combined with Pydev. Besides syntax highlighting you'll also get more fancy features to help you debug and refactor your code.
Personally I use Emacs with python-mode (and a few other modes to interface with Subversion and Git). In the past I used Vim which also worked quite well.
My advice would be to start out with your current environment as long as it has some rudimentary support for Python. Once you are familiar with the language, start exploring what your environment is missing and either add it or if you cannot, switch to an enviroment which does support the feature.

I use gvim with some plugin in order to have better support for python.
If you like IDE, look at wing IDE wich is the best I have tested so far. Especially the debuger included is really helpful.

The Python Beginner's Guide and the official Python Tutorial both seem like good places to start.

Geany is a good option for a Linux setup, it's intellisense isn't that great but syntax highlighting is good and it can compile your code directly from inside the editor, plus it handles other languages such as C/C++, PHP, Java etc... Eric is another popular choice as it's a full IDE and I know some people use Eclipse.
On windows I use Notepad++, but it's mostly because I like text editors instead of fully blown IDE's.
Reference wise Daniel's choices are very good places to start, also check out Green Tea Press who do free computer books, there are two Python choices on there but the "Python for Software Design" book hasn't yet been published properly although you can download the manuscript. The "How to Think Like a Computer Scientist" book is a good one and not as scary as it sounds.

IDLE is nice to try out things. Other tools that people like are Eclipse with the Pydev plugin which seems to work ok, although it has crashed a few times (Eclipse, that is) and NetBeans (which I haven't tried) but some people seem to like.

I can only help you if you're running a Mac. Download Xcode. I believe that Python 2.3 comes bundled with these development tools. Luckily enough, this is all you really need to get started, unless you want a newer version of Python.
All you need to do is open up Terminal and type python. You're done!