Using Python in vimscript: How to export a value from a python script back to vim?

Question

I'm struggling with Python in vim.
I still haven't found out how I can import a value from a python script (in a vim function) back to vim p.e.

function! myvimscript()

  python << endpython
    import vim, random, sys
    s = vim.eval("mylist")
    # do operation with variable "s" in python
  endpython

  " import variable "s" from above 
  " do operation with "s" in vimscript
endfunction

1) How can I use "s" again in vim (how can I import "s" from the python code back to vim)?

I can't find out as well how to use vim.current.buffer with a selection.

function! myvimscript()
  let startline = line("'<")
  let endline = line("'>")

  python << endpython
    start = vim.eval("startline")
    end = vim.eval("endline")
    cb = vim.current.buffer 
    l = cb[start:end]
  endpython
endfunction

2) How can I assign the dynamic value "start" and "end" to "l"

@TallPaul, Un pythonscript running in a vimscript (and invoked with a map in vimrc) — Reman
– Reman, Commented Jul 15, 2013 at 14:46
Related: How do I get the value returned from a function in Python & Vimscript?. — glts
– glts, Commented Jul 15, 2013 at 15:32
Note: this basic approach of printf-style string interpolation vim.command("let sInVim = '%s'"% s) is a source of potential bugs. Specifically, this approach will not work as expected if the interpolated value causes delimiter collision on the single-quote character — dreftymac
– dreftymac, Commented Nov 22, 2022 at 19:24

Kent · Accepted Answer · 2013-07-15 15:47:30Z

28

First of all, please define your function name starting with uppercase.

Here is an example for your two questions. I hope it helps:

function! TestPy() range

    let startline = line("'<")
    let endline = line("'>")
    echo "vim-start:".startline . " vim-endline:".endline
python << EOF
import vim
s = "I was set in python"
vim.command("let sInVim = '%s'"% s)
start = vim.eval("startline")
end = vim.eval("endline")
print "start, end in python:%s,%s"% (start, end)
EOF
    echo sInVim
endfunction

first I paste the output of a small test: I visual selected 3,4,5, three lines, and :call TestPy()

The output I had:

vim-start:3 vim-endline:5
start, end in python:3,5
I was set in python

So I explain the output a bit, you may need to read the example function codes a little for understanding the comment below.

vim-start:3 vim-endline:5   #this line was printed in vim,  by vim's echo.
start, end in python:3,5    # this line was prrinted in py, using the vim var startline and endline. this answered your question two.
I was set in python         # this line was printed in vim, the variable value was set in python. it answered your question one.

I added a range for your function. because, if you don't have it, for each visual-selected line, vim will call your function once. in my example, the function will be executed 3 times (3,4,5). with range, it will handle visualselection as a range. It is sufficient for this example. If your real function will do something else, you could remove the range.

With range, better with a:firstline and a:lastline. I used the line("'<") just for keep it same as your codes.

EDIT with list variable:

check this function:

function! TestPy2()
python << EOF
import vim
s = range(10)
vim.command("let sInVim = %s"% s)
EOF
    echo type(sInVim)
    echo sInVim
endfunction

if you call it, the output is:

3
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

the "3" means type list (check type() function). and one line below is the string representation of list.

edited Jul 15, 2013 at 15:47

answered Jul 15, 2013 at 14:57

Kent

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5 Comments

Reman Over a year ago

great explication Kent! But what if s is not a string but a list. It gives errors with vim.command("let sInVim = '%s'"% s)

Reman Over a year ago

Thank you very much. I will study your answer a bit more. You gave me so much information. But now everything works fine!

Reman Over a year ago

Now with you info I'm trying to test a random function using python.

:py import vim, random as r; cb = vim.current.buffer ; start = vim.eval('line("'<")'); end = vim.eval('line("'>")'); l = cb[start:end] ; r.shuffle(l) ; cb[start:end] = l

Something still doesn't work. error: must be string not bool.

Reman Over a year ago

Found the solution :) I had to declare the variables 'start' and 'end' as integers :)

mMontu Over a year ago

For global variables there is another option for vim.command("let sInVim = '%s'"% s): vim.vars["sInVim"] = s

tossbyte · Accepted Answer · 2019-05-30 19:05:30Z

5

As of v7.3.569, vim built-in functions pyeval() and py3eval() allow you to evaluate a python expression, and return its result as a vimscript value. It can handle simple scalar values, but also lists and dictionaries - see :help pyeval()

On 1): For using a python-defined variable in vim:

python << endPython
py_var = 8
endPython

let vim_var = pyeval('py_var')

On 2): I assume you want the buffer lines last highlighted in visual mode, as a list of strings in vimscript:

python << endPython
import vim
cb = vim.current.buffer
start = int(vim.eval("""line("'<")"""))
end = int(vim.eval("""line("'>")"""))
lines = cb[(start - 1) : end]
endPython
let lines = pyeval('lines')

Note: This is a somewhat contrived example, as you could get the same directly in vimscript:

let lines = getline("'<", "'>")

edited May 30, 2019 at 19:05

answered May 30, 2019 at 18:52

tossbyte

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6 Comments

Reman Over a year ago

I use this one: python << endPython | my_val = ... | vim.command("let my_val = '%s'" % my_val) | endpython || let vim_val = my_val What is the difference between both?

tossbyte Over a year ago

@Reman: pyeval might facilitate using existing python libs, which are usually not aware of vim context. Also, with vim.command, lists and dictionaries might be slightly more brittle, due to potential quoting issues.

Reman Over a year ago

rippleslash, does it also work with Python 3.7? I do receive errors after having changed a few vim.command in ...pyeval(): "cannot find python library 2.7" - I don't use python 2.7

Reman Over a year ago

rippleslash, what to do if a list or dictionary has only integers? py3eval() can't convert the object: E859: Failed to convert returned python object to vim value

tossbyte Over a year ago

@Reman, py3eval("[1, 2, 3]") and py3eval("{ 'foo': 1 }") seem to work, but py3eval("{ 1: 'foo' }") doesn't (tried in vim 8.1.1137). According to :help Dictionary, vim always uses strings as dict keys, maybe that's why it fails in this case. Best I can think of is to stringify your dict keys - i.e. def convert(d): return { str(k): v for k, v in d.items() } in python and py3eval("convert({ 1: 'foo' })") in vim.

|

Tinmarino · Accepted Answer · 2019-12-12 05:53:37Z

1

In short:

:py3 vim.command("let vimvar = '%s'" % 'pyvalue')

or

:let vimvar = py3eval("'pyvalue'")

Where vimvar is a vim variable and can be b: w: t: g: l: s: a: v: and 'pyvalue' is a python variable.

answered Dec 12, 2019 at 5:53

Tinmarino

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1 Comment

dreftymac Over a year ago

Note: this basic approach of printf-style string interpolation vim.command("let sInVim = '%s'"% s) is a source of potential bugs. Specifically, this approach will not work as expected if the interpolated value causes delimiter collision on the single-quote character

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