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~.