Deceptively minimalistic Python IDE for GNU Emacs.
Q: How many keys does it take to define/redefine a Python function?
A: One - e
.
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
.
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.
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: 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
.
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.
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.
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
.