* lpy

Deceptively minimalistic Python IDE for GNU Emacs.

* Setup
Install from MELPA and enable =lpy-mode=.

* Introduction
Q: How many keys does it take to define/redefine a Python function?
A: One - ~e~.

** Arrow navigation
Q: Does this also apply to classes, import statements, for loops and
plain one liners?
A: Of course.

Q: How many keys does it take to move to the next Python function?
A: One - ~j~.

Q: Does this also apply to classes, import statements, for loops and
plain one liners?
A: Of course.

Q: So, how do I eval a statement, move to the second statement, and
eval the second statement?
A: ~eje~.

Q: How to move back to the first statement?
A: ~k~.

Q: How do I descent into a compound statement, like =def=?
A: ~l~.

Q: How do I ascent back?
A: ~h~.

Q: Back to eval, how do I eval something that's not a compound
statement?
A: Mark as much legal code as you like with a region and press ~e~.

Q: Any shortcut for marking a symbol in order to eval it?
A: ~M-m~.

** Semantic navigation
Q: How can I select a top-level symbol in the current file?
A: ~g~.

Q: How do I follow to the current symbol's definition?
A: ~M-.~.

Q: How do I go back from there?
A: =M-,=.

Q: Does =M-,= also bring me back after ~g~?
A: Yes.

** Eval in more detail
Q: Where do I see the result of the eval?
A: In the minibuffer.

Q: What if the result of the operation is =None=?
A: Then =(ok)= is printed to confirm that the operation went through.

Q: What if an uncaught exception is thrown?
A: The exception will be displayed in the minibuffer, highlighted in
red.

Q: Is it possible to be productive without ever seeing the REPL
buffer?
A: Yes.

Q: How do I see the REPL buffer?
A: ~C-c C-z~.

Q: Can I have more than one REPL session?
A: Yes, use ~xp~ to select session or start a new one.

Q: Does pressing ~e~ on a variable assignment output nothing because the
result is =None=?
A: No, magic is used to make it print the new value of the variable.

Q: Where else is ~e~ magical?
A: ~e~ on  =__file__= will print the actual file name.

Q: Any more?
A: ~e~ on a single line =return= statement will print the return result.

Q: How do I insert the result of the eval into the buffer?
A: ~E~.

Q: How do I insert the result of the eval into the buffer as a
comment?
A: ~2e~.

Q: Howto easily select things to eval?
A: ~M-m~ to get into special. Then ~+~ and ~-~ to expand/shrink selection with =expand-region=.

** Debugging
Q: How do I step into an expression?
A: ~xj~.

Q: Where does this work?
A: Function or method call, possibly with the result being assigned to
a variable.

Q: What does that do exactly?
A: Evaluate the function arguments, jump to the function definition,
and store the function arguments into global variable with appropriate
names.

Q: So if all I have is =sys.argv= I can use ~xj~ (combined with ~j~, ~l~ and
~e~) to step into my program as deep as I want?
A: Yes.

Q: What if I just want to place a breakpoint to speed things up?
A: To place a breakpoint, throw any exception. Then, enter
=lp.pm()= into the REPL.

Q: =lp.pm()= sounds weird, how can I see how it works?
A: Enter into the REPL: =os.path.realpath(42)= which will raise an
exception a few functions down the line. Then enter =lp.pm()=.

Q: Wait, so this is like =pdb=?
A: Yes, very similar.

Q: So why go through the trouble?
A: To get global variable context and proceed with ~e~ and ~j~.

Q: Got it. Anyway, I see =File "/usr/lib/python2.7/posixpath.py",
line 61, Frame [3/3]:=, what does it mean?
A: =realpath= called =_joinrealpath=, which called =isabs=, which raised an
Exception.

Q: Three functions (=realpath=, =_joinrealpath=, and =isabs=), that's what
3/3 means. And I'm in =isabs= now?
A: Yes.

Q: How do I open the source code for =isabs=?
A: It's a link: use the mouse or =ace-link= or =next-error=.

Q: I'm at the definition of =isabs= now, was its argument value stored
somewhere?
A: Yes, if you eval =s=, you get =42= - the value that propagated from
=os.path.realpath(42)=.

Q: =isabs= is boring. How do I go up the stack?
A: Enter =up= into the REPL.

Q: I entered up, and now the frame is 2/3 and
I'm at =def _joinrealpath(path, rest, seen)=. Does this mean I can eval
=path=, =rest=, and =seen= since they were propagated from the
=os.path.realpath(42)= call?
A: Yes.

Q: And entering =up= again will bring me to 1/3 and =realpath=?
A: Yes.

Q: How do I go back down stack?
A: Enter =dn=.

** Notebooks
Q: Is this like IPython?
A: Yes.

Q: But it's different how?
A: You use Emacs instead of a browser, and the cells are
self-contained in comments.

Q: Sounds nice, but I'm not sold yet?
A: It's like Org-mode embedded in Python code.

Q: So I can fold / unfold each cell?
A: Yes.

Q: And eval/reeval it with ~e~?
A: Yes.

Q: How about organizing cells in a hierarchy?
A: Also possible.

Q: And ~e~ works on the hierarchy as well?
A: Yes.

Q: Are cells actually called different or something?
A: Yes, they're outlines.

Q: How do I make an outline named =Includes=?
A: Enter =#* Includes=.

Q: And like in Org-mode, the amount of stars is that outline's level?
A: Yes.

Q: Do ~M-left~ and ~M-right~ work like in Org-mode for promotion/demotion?
A: Yes.

Q: How to fold/unfold an outline?
A: ~i~.

Q: How do I fold/unfold all outlines?
A: ~I~.

Q: How do I make a table of contents?
A: ~2I~.

Q: When I press ~e~ on an outline it evaluates itself and the result is
echoed; how do I make the result insert itself into the buffer
instead?
A: End the outline name in =:= (semicolon)

Q: How do I clean up all inserted results?
A: ~M-x~ =lpy-clean=.

Q: Any more neat stuff about outlines?
A: Yes, outlines are structured statements and parents to the
top-level statements.

Q: So ~j~ / ~k~ and ~h~ / ~l~, and even ~e~ treat outlines as statements? Neat.
A: Yeah.

** Completion
Q: How do I get completion at point?
A: Press ~C-M-i~.

Q: Is this static completion or does it depend on the REPL state?
A: Both. The static one is more convenient and is tried first. But the
dynamic one is very reliable, since it knows exactly on which type of
object you're operating.

Q: But dynamic completion won't work unless my current object has a
value in the REPL?
A: Correct.

Q: What's used for static completion?
A: Jedi.

** Inline hints
Q: How do I look up the function arguments of the current function?
A: Toggle ~C-2~.

Q: What about the docstring?
A: Toggle ~C-1~.