Run python in scratch buffer.

[linusboehm]

I really like the option to run lua in a scratch buffer (default keyboard shortcut is: <leader>. to open the scratch buffer and then <cr> to execute the lua snippet.

I wanted a similar behavior for python and added the following to my config. It executes the python snipped and shows the result in a scratch buffer at the bottom. Thought it might be helpful for others:

local defaults = {
  name = "Output",
  ft = vim.bo.filetype,
  ---@type string|string[]?
  icon = nil, -- `icon|{icon, icon_hl}`. defaults to the filetype icon
  win = { style = "output" },
}

local height = 20
Snacks.config.style("output", {
  width = 0,
  height = height,
  backdrop = false,
  row = vim.api.nvim_get_option_value("lines", {}) - height,
  bo = { buftype = "nofile", buflisted = false, bufhidden = "wipe", swapfile = false, undofile = false },
  minimal = false,
  noautocmd = false,
  zindex = 100,
  ft = "output",
  wo = { winhighlight = "NormalFloat:Normal", colorcolumn = "" },
})

--- Show lines in a floating buffer at the bottom.
---@param lines string
---@param opts? snacks.scratch.Config
local function show_output(lines, opts)
  opts = Snacks.config.get("output", defaults, opts)
  opts.win = Snacks.win.resolve("output", opts.win, { show = false })

  local out_buf = vim.api.nvim_create_buf(false, true)

  local content = {}
  for line in lines:gmatch("([^\n]*)\n?") do
    table.insert(content, line)
  end
  -- Remove trailing empty lines
  for i = #content, 1, -1 do
    if content[i] == "" then
      table.remove(content, i)
    else
      break
    end
  end
  vim.api.nvim_buf_set_lines(out_buf, 0, -1, false, content)
  opts.win.buf = out_buf
  return Snacks.win(opts.win):show()
end

--- Run the current buffer or a range of lines.
--- Shows the output in a scratch buffer at the bottom.
---@param opts? {name?:string, buf?:number, print?:boolean}
local function runPython(opts)
  local ns = vim.api.nvim_create_namespace("snacks_debug")
  opts = vim.tbl_extend("force", { print = true }, opts or {})
  local buf = opts.buf or 0
  buf = buf == 0 and vim.api.nvim_get_current_buf() or buf
  local name = opts.name or vim.fn.fnamemodify(vim.api.nvim_buf_get_name(buf), ":t")

  -- Get the lines to run
  local lines ---@type string[]
  local mode = vim.fn.mode()
  if mode:find("[vV]") then
    if mode == "v" then
      vim.cmd("normal! v")
    elseif mode == "V" then
      vim.cmd("normal! V")
    end
    local from = vim.api.nvim_buf_get_mark(buf, "<")
    local to = vim.api.nvim_buf_get_mark(buf, ">")

    -- for some reason, sometimes the column is off by one
    -- see: https://github.com/folke/snacks.nvim/issues/190
    local col_to = math.min(to[2] + 1, #vim.api.nvim_buf_get_lines(buf, to[1] - 1, to[1], false)[1])

    lines = vim.api.nvim_buf_get_text(buf, from[1] - 1, from[2], to[1] - 1, col_to, {})
    -- Insert empty lines to keep the line numbers
    for _ = 1, from[1] - 1 do
      table.insert(lines, 1, "")
    end
    vim.fn.feedkeys("gv", "nx")
  else
    lines = vim.api.nvim_buf_get_lines(buf, 0, -1, false)
  end

  -- Clear diagnostics and extmarks
  local function reset()
    vim.diagnostic.reset(ns, buf)
    vim.api.nvim_buf_clear_namespace(buf, ns, 0, -1)
  end
  reset()
  vim.api.nvim_create_autocmd({ "TextChanged", "TextChangedI" }, {
    group = vim.api.nvim_create_augroup("snacks_debug_run_" .. buf, { clear = true }),
    buffer = buf,
    callback = reset,
  })

  local command = "echo " .. vim.fn.shellescape(table.concat(lines, "\n")) .. " | python3 2>&1"
  local handle = io.popen(command)
  if not handle then
    Snacks.notify.error("Didn't get popen handle.", { title = name })
    return
  end
  local out = handle:read("*a")
  handle:close()

  if out == "" then
    Snacks.notify.info("No output.", { title = name, ft = "python" })
  else
    show_output(out)
  end
end

and then in the opts for the snacks lazyvim config:

    scratch = {
      enabled = true,
      win_by_ft = {
        python = {
          keys = {
            ["source"] = {
              "<cr>",
              function(self)
                local name = "scratch." .. vim.fn.fnamemodify(vim.api.nvim_buf_get_name(self.buf), ":e")
                runPython({ buf = self.buf, name = name })
              end,
              desc = "Source buffer",
              mode = { "n", "x" },
            },
          },
        },
      },
    },

This works for the entire buffer and the current visual selection and shows tracebacks in case of an error in the python script. Most of the runPython function is based on the function that is used to execute lua snippets.