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.