Thread by @SebaWitowski

Since everyone is doing the Advent of Code, I want to do something else - the #IPython Advent Calendar.
IPython is great to interactively solve problems like this, and I want to show you some tips to make the most of it.
So 25 tips for 25 days 👇

1. You can display useful information for any function, module, or variable by adding "?" at the end (or at the beginning). No need to google for the documentation.

2. If you want to see the whole source code of a function (or a class/module), add two question marks instead of one:
your_function??

3. If you want to write a longer function, use "%edit" command.
IPython will open a temporary file in your favorite editor (you need to set it with the EDITOR environment variable), and when you save and close it, it will execute that code.

4. Speaking of the %edit command, you can run "%edit -p" to reopen the same file that you edited last time. This is great to incrementally build some bigger code block or to quickly fix a mistake you made last time.

5. Forgot how some function is called? You can use * for wildcard search in a module or class. For example, os.*dir*? returns all functions from the os module that contain "dir" in their names.

6. Post-mortem debugging is 🚀!
When an exception happens, run %debug, and it will start a debugger for that past exception.
Great way to debug unexpected exceptions (unexpected == you didn't think it's going to fail, so you didn't enable the debugger before running your code).

7. Run %pdb to automatically start a debugger on every exception (run %pdb again to disable it).

8. Run shell commands directly from IPython by prefixing them with "!".
Wanna run vim from IPython? Why not ("!vim")?!
Node REPL inside IPython REPL? Sure ("!node")!
Drop your file system ("!rm -rf /") - well, maybe not 😅

6. Post-mortem debugging is 🚀!
When an exception happens, run %debug, and it will start a debugger for that past exception.
Great way to debug unexpected exceptions (unexpected == you didn't think it's going to fail, so you didn't enable the debugger before running your code).

7. Run %pdb to automatically start a debugger on every exception (run %pdb again to disable it).

8. Run shell commands directly from IPython by prefixing them with "!".
Wanna run vim from IPython? Why not ("!vim")?!
Node REPL inside IPython REPL? Sure ("!node")!
Drop your file system ("!rm -rf /") - well, maybe not 😅

9. You can move around the filesystem with %cd without leaving IPython. If you started IPython in a "wrong" folder, you can move with "%cd some/other/folder". You also get autocompletion for folder names when pressing TAB.

10. Use "%autoreload" to automatically reload any imported function/module before running them.
It's great when you want to edit code in one window and run it in IPython without reimporting it every time (more info here: switowski.com/blog/ipython-a…).

11. Use %xmode to change how verbose the errors are. Each time you run it, it changes between Minimal (almost no information)->Plain->Context (default value)->Verbose (LOTS of information)->Minimal.

The verbose mode prints values of the local variables in the stack trace.

Use "%rerun ~1/" to automatically rerun all the commands from the previous IPython session.

Unfortunately, it won't work if you had exceptions (rerun stops after every exception) or if the last session also contains "%rerun ~1/" (it will start a weird recursion and fail).

13. Want to execute some code each time you start IPython? Add it in the "startup" folder. It's a great way to automatically import some modules that you use all the time.

14. You can create a new profile with different settings. For example, you can create a profile just for debugging with verbose exceptions and plenty of debugging/profiling libraries automatically imported.

15. Output of the last command is stored in variable _
If you forgot to assign an expression to a variable, use var = _. Outputs from older commands are stored in variables constructed by adding a cell number to _. So _1 is the output of the first command in the current session.

16. You can edit ANY function or module (even those installed with pip) - just run "%edit function_name". IPython will find the source code of that function and open it for editing.

Below, I'm breaking the built-in randint() function by making it always return 42.

17. Want to share your code with someone? Run %pastebin <line numbers> (e.g. %pastebin 1-5) - this will take the first 5 lines from IPython, create an online pastebin (it's like GitHub gist), and return a link that you can send to someone.

18. Want to use IPython as a debugger?
Install "ipdb" and either use "ipdb.set_trace()" or run "export PYTHONBREAKPOINT=ipdb.set_trace" and use the built-in "breakpoint()" statement (requires Python >= 3.7). Thanks to @mborus for this idea!

@mborus 19. Want to execute code from another language? Type %%ruby, write some ruby code, press Enter twice, and IPython will run it without problems. It works for other languages, too (including Python 2).

18,5. And if you just want to start an IPython session in a specific place in your code (not as a debugger), drop the "from IPython import embed; embed()" line there.

@mborus 20. Use %store to save variables in IPython's database. That way, you can restore it with "%store -r variable" in another IPython session. Or set 'c.StoreMagics.autorestore = True' in configuration to automatically restore all variables each time you start IPython.

21. If you want to save your IPython session to a file and turn it into a proper program, use "%save filename.py first_cell-last_cell".
Then open https://t.co/vL2FCpvS8m in your editor and remove lines that you don't need. Et voilà! You have a Python script!

22. If you need to clean up code with an incorrect indentation or trailing ">" characters (for example, when copying from an email), copy that code and run %paste.

IPython will try to automatically fix the indentation, remove > characters and execute the code from the clipboard.

23. To see all the variables from the current session with their types and values, run %whos.

24. Do you want to speed up your code with asynchronous functions? IPython has an event loop built-in, so you can write and run async functions just like regular functions (it's called %autoawait and can be turned off if you want to start your own event loop).

25. You can run scripts that contain IPython-specific syntax (shell commands or magic commands). Just save them with the .ipy extension and run them with the "ipython filename.ipy" command.