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CREATED

2023-10-05

UPDATED

5 days ago

Molten

Molten is a fork of Magma, a plugin for running code interactively with the jupyter kernel. Molten provides an excellent repl-like experience, and an incredible notebook-like experience in neovim.

https://github.com/benlubas/molten-nvim/assets/56943754/17ae81c0-306f-4496-bce8-99286e7f21ed

Feature Highlights

Send code to run asynchronously in the jupyter kernel
See output below the code in real time, without flicker, as virtual text or in a floating window (or both)
Renders images, plots, and LaTeX in neovim
Take input from stdin with vim.ui.input
Send code from multiple buffers to the same kernel
Send code from the same buffer to multiple kernels
Supports any language with a Jupyter Kernel (in theory, they haven't all been tested)
Python virtual environment support
Import and Export outputs to and from jupyter notebook files

Requirements

NeoVim 9.4+
Python 3.10+
image.nvim is only required for the image.nvim image provider
wezterm.nvim is only required for the wezterm image provider
Required Python packages (can be installed in a venv. read more):
- pynvim (for the Remote Plugin API)
- jupyter_client (for interacting with Jupyter)
Optional Python packages:
- cairosvg (for displaying SVG images with transparency)
  - If you don't need transparency, image.nvim can render svg images perfectly fine
- pnglatex (for displaying TeX formulas)
- plotly and kaleido (for displaying Plotly figures)
- pyperclip if you want to use molten_copy_output
- nbformat for importing and exporting output to jupyter notebooks files
- pillow for opening images with :MoltenImagePopup

You can run :checkhealth to see what you have installed.

Note: Optional python packages are only imported when they're used.

Quick-start

For the impatient: Probably Too Quick Start Guide
For everyone else: Not So Quick Start Guide
Windows users also read this
NixOS users can checkout this

Configuration information is located further down in this README.

To setup molten for editing Jupyter Notebook files, see Notebook Setup.

Usage

Start by initializing a kernel. This kernel will get a kernel_id which is most commonly just the name of the kernel. If you try to initialize two kernels with the same name, the second one will be named kernel_name_n where n is the total number of kernels that are already initialized.

You execute code by sending it to a kernel, specified by its kernel_id (this is handled automatically if there is only one option).

When you execute some code, it will create a cell. You can recognize a cell because it will be highlighted when your cursor is in it.

A cell is delimited using two extmarks (see :h api-extended-marks), so each cell will adjust when editing text within its boundaries.

When your cursor is in a cell (i.e., you have an active cell), a floating window may be shown below the cell, reporting output. This is the floating output window. (To see more about whether a window is shown or not, see :MoltenShowOutput and g:molten_auto_open_output). When you cursor is not in any cell, no cell is active. When your cursor leaves a cell, its floating output window will close.

Output may also be displayed as virtual text below a cell. Virtual text output will stay there until you re-run the cell or delete the cell.

Overlapping cells are not allowed. If you create an overlapping cell, the old cell will be deleted.

The output window has a header, containing the execution count and execution state (i.e., whether the cell is waiting to be run, running, has finished successfully or has finished with an error). Below the header, output is shown.

Jupyter provides a rich set of outputs. To see what we can currently handle, see Output Chunks.

Commands

These user commands are the main interface to the plugin. It is recommended to map most of them to keys, as explained in Keybindings.

Here is a list of the commands and their arguments. Args in [] are optional, args in "" are literal.

When the kernel argument is specified as optional the command behaves in the following way:

if the kernel is specified, send the code to that kernel
else if there is only one active kernel for the current buffer, send the code to that kernel
else if there is more than one active kernel for the current buffer, prompt the user for the kernel

Some commands will prompt for a kernel when they require one, but no kernel is attached to the buffer. This is configurable with the molten_auto_init_behavior option.

Command	Arguments	Description
`MoltenInfo`	none	Show information about the state of the plugin, initialization status, available kernels, and running kernels
`MoltenInit`	`["shared"] [kernel]`	Initialize a kernel for the current buffer. If `shared` is passed as the first value, this buffer will use an already running kernel. If no kernel is given, prompts the user.
`MoltenDeinit`	none	De-initialize the current buffer's runtime and molten instance. (called automatically on vim close/buffer unload)
`MoltenGoto`	`[n]`	Go to the `n`th code cell `n` defaults to 1 (1 indexed)
`MoltenNext`	`[n]`	Go to the next code cell, or jump `n` code cells `n` defaults to 1. Values wrap. Negative values move backwards
`MoltenPrev`	`[n]`	like `Next` but backwards
`MoltenEvaluateLine`	`[kernel]`	Evaluate the current line
`MoltenEvaluateVisual`	`[kernel]`	Evaluate the visual selection (cannot be called with a range!)
`MoltenEvaluateOperator`	`[kernel]`	Evaluate text selected by the following operator. see Keybindings for useage
`MoltenEvaluateArgument`	`[kernel] code`	Evaluate given code in the given kernel
`MoltenReevaluateCell`	none	Re-evaluate the active cell (including new code) with the same kernel that it was originally evaluated with
`MoltenDelete`	none	Delete the active cell (does nothing if there is no active cell)
`MoltenShowOutput`	none	Shows the output window for the active cell
`MoltenHideOutput`	none	Hide currently open output window
`MoltenEnterOutput`	none	Move into the active cell's output window. Opens but does not enter the output if it's not open. must be called with `noautocmd` (see Keybindings for example)
`MoltenInterrupt`	`[kernel]`	Sends a keyboard interrupt to the kernel which stops any currently running code. (does nothing if there's no current output)
`MoltenOpenInBrowser`	none	Open the current output in the browser. Currently this only supports cells with `'text/html'` outputs, configured with `molten_auto_open_html_in_browser` and `molten_open_cmd`
`MoltenImagePopup`	none	Open an image from the current output with python's `Image.show()`. This will use your system's default image viewer, this behavior can happen automatically (see: `molten_auto_image_popup`)
`MoltenRestart`	`[!] [kernel]`	Shuts down a restarts the kernel. Deletes all outputs if used with a bang
`MoltenSave`	`[path] [kernel]`	Save the current cells and evaluated outputs into a JSON file. When path is specified, save the file to `path`, otherwise save to `g:molten_save_path`. currently only saves one kernel per file
`MoltenLoad`	`["shared"] [path]`	Loads cell locations and output from a JSON file generated by `MoltenSave`. path functions the same as `MoltenSave`. If `shared` is specified, the buffer shares an already running kernel.
`MoltenExportOutput`	`[!] [path] [kernel]`	Export outputs from the current buffer and kernel to a jupyter notebook (`.ipynb`) at the given path. read more
`MoltenImportOutput`	`[path] [kernel]`	Import outputs from a jupyter notebook (`.ipynb`). read more

Keybindings

The commands above should be mapped to keys for the best experience.

Pay attention to MoltenEvaluateVisual and MoltenEnterOutput, as they need to be run in...odd ways.

Minimum Suggested

vim.keymap.set("n", "<localleader>mi", ":MoltenInit<CR>",
    { silent = true, desc = "Initialize the plugin" })
vim.keymap.set("n", "<localleader>e", ":MoltenEvaluateOperator<CR>",
    { silent = true, desc = "run operator selection" })
vim.keymap.set("n", "<localleader>rl", ":MoltenEvaluateLine<CR>",
    { silent = true, desc = "evaluate line" })
vim.keymap.set("n", "<localleader>rr", ":MoltenReevaluateCell<CR>",
    { silent = true, desc = "re-evaluate cell" })
vim.keymap.set("v", "<localleader>r", ":<C-u>MoltenEvaluateVisual<CR>gv",
    { silent = true, desc = "evaluate visual selection" })

Other example mappings

vim.keymap.set("n", "<localleader>rd", ":MoltenDelete<CR>",
    { silent = true, desc = "molten delete cell" })
vim.keymap.set("n", "<localleader>oh", ":MoltenHideOutput<CR>",
    { silent = true, desc = "hide output" })
vim.keymap.set("n", "<localleader>os", ":noautocmd MoltenEnterOutput<CR>",
    { silent = true, desc = "show/enter output" })

Configuration

Configuration is done with variables. Below you'll find a table of all the potential configuration variable, their values, and a brief description.

the default value is wrapped in ()

Variable	Values	Description
`g:molten_auto_image_popup`	`true` \| (`false`)	When true, cells that produce an image output will open the image output automatically with python's `Image.show()`
`g:molten_auto_init_behavior`	`"raise"` \| (`"init"`)	When set to "raise" commands which would otherwise ask for a kernel when they're run without a running kernel will instead raise an exception. Useful for other plugins that want to use `pcall` and do their own error handling
`g:molten_auto_open_html_in_browser`	`true` \| (`false`)	Automatically open HTML outputs in a browser. related: `molten_open_cmd`
`g:molten_auto_open_output`	(`true`) \| `false`	Automatically open the floating output window when your cursor moves into a cell
`g:molten_cover_empty_lines`	`true` \| (`false`)	The output window and virtual text will be shown just below the last line of code in the cell.
`g:molten_cover_lines_starting_with`	(`{}`) \| array of str	When `cover_empty_lines` is true, also covers lines starting with these strings
`g:molten_copy_output`	`true` \| (`false`)	Copy evaluation output to clipboard automatically (requires `pyperclip`)
`g:molten_enter_output_behavior`	(`"open_then_enter"`) \| `"open_and_enter"` \| `"no_open"`	The behavior of MoltenEnterOutput
`g:molten_image_provider`	(`"none"`) \| `"image.nvim"` \| `"wezterm"` \|	How images are displayed see Images for more details
`g:molten_open_cmd`	(`nil`) \| Any command	Defaults to `xdg-open` on Linux, `open` on Darwin, and `start` on Windows. But you can override it to whatever you want. The command is called like: `subprocess.run([open_cmd, filepath])`
`g:molten_output_crop_border`	(`true`) \| `false`	'crops' the bottom border of the output window when it would otherwise just sit at the bottom of the screen
`g:molten_output_show_exec_time`	(`true`) \| `false`	Shows the current amount of time since the cell has begun execution
`g:molten_output_show_more`	`true` \| (`false`)	When the window can't display the entire contents of the output buffer, shows the number of extra lines in the window footer (requires nvim 10.0+ and a window border)
`g:molten_output_virt_lines`	`true` \| (`false`)	Pad the main buffer with virtual lines so the floating window doesn't cover anything while it's open
`g:molten_output_win_border`	(`{ "", "━", "", "" }`) \| any value for `border` in `:h nvim_open_win()`	Some border features will not work if you don't specify your border as a table. see border option of `:h nvim_open_win()`
`g:molten_output_win_cover_gutter`	(`true`) \| `false`	Should the output window cover the gutter (numbers and sign col), or not. If you change this, you probably also want to change `molten_output_win_style`
`g:molten_output_win_hide_on_leave`	(`true`) \| `false`	After leaving the output window (via `:q` or switching windows), do not attempt to redraw the output window
`g:molten_output_win_max_height`	(`999999`) \| int	Max height of the output window
`g:molten_output_win_max_width`	(`999999`) \| int	Max width of the output window
`g:molten_output_win_style`	(`false`) \| `"minimal"`	Value passed to the `style` option in `:h nvim_open_win()`
`g:molten_save_path`	(`stdpath("data").."/molten"`) \| any path to a folder	Where to save/load data with `:MoltenSave` and `:MoltenLoad`
`g:molten_split_direction`	(`"right"`) \| `"left"` \| `"top"` \| `"bottom"` \|	Direction of the terminal split created by wezterm. Only applies if `g:molten_image_provider = "wezterm"`
`g:molten_split_size`	(`40`) \| int	(0-100) % size of the screen dedicated to the output window. Only applies if `g:molten_image_provider = "wezterm"`
`g:molten_tick_rate`	(`500`) \| int	How often (in ms) we poll the kernel for updates. Determines how quickly the ui will update, if you want a snappier experience, you can set this to 150 or 200
`g:molten_use_border_highlights`	`true` \| (`false`)	When true, uses different highlights for output border depending on the state of the cell (running, done, error). see highlights
`g:molten_limit_output_chars`	(`1000000`) \| int	Limit on the number of chars in an output. If you're lagging your editor with too much output text, decrease it
`g:molten_virt_lines_off_by_1`	`true` \| (`false`)	Allows the output window to cover exactly one line of the regular buffer when `output_virt_lines` is true, also effects where `virt_text_output` is displayed. (useful for running code in a markdown file where that covered line will just be ```)
`g:molten_virt_text_output`	`true` \| (`false`)	When true, show output as virtual text below the cell, virtual text stays after leaving the cell. When true, output window doesn't open automatically on run. Effected by `virt_lines_off_by_1`
`g:molten_virt_text_max_lines`	(`12`) \| int	Max height of the virtual text
`g:molten_wrap_output`	`true` \| (`false`)	Wrap output text
[DEBUG] `g:molten_show_mimetype_debug`	`true` \| (`false`)	Before any non-iostream output chunk, the mime-type for that output chunk is shown. Meant for debugging/plugin devlopment

Images

Molten has two image providers, image.nvim or wezterm:

image.nvim requires the image.nvim plugin (and it's dependencies). It renders images in neovim inline with other cell output. This creates a better experience, but it can be buggy with large numbers of images, and it does not work on Windows.
wezterm requires the wezterm.nvim plugin (and the wezterm terminal emulator). It renders images in a wezterm split pane using wezterm's imgcat program. This method is significantly less buggy with large numbers of images and works on Windows, but it doesn't keep images next to the code they came from.
- Cannot be used with g:molten_auto_open_output = true
- Configurable with the g:molten_split_direction and g:molten_split_size options.
- Currently, the wezterm image provider does not integrate with tmux. There are issues with allowing images to passing through tmux to wezterm. If you are using tmux, you will need to use the image.nvim image provider.

Status Line

Molten provides a few functions that you can use to see information in your status line. These are listed below:

require('molten.status').initialized() -- "Molten" or "" based on initialization information
require('molten.status').kernels() -- "kernel1 kernel2" list of kernels attached to buffer or ""
require('molten.status').all_kernels() -- same as kernels, but will show all kernels

The way these are used will vary based on status line plugin. So please refer to your status line plugin to figure out how to use them.

Highlights

You can change highlights like so:

-- see :h nvim_set_hl for what to put in place of ...
-- I would recommend using the `link` option to link the values to colors from your color scheme
vim.api.nvim_set_hl(0, "MoltenOutputBorder", { ... })

Here is a complete list of the highlight groups that Molten uses, and their default values

MoltenOutputBorder = FloatBorder: default output window border
MoltenOutputBorderFail = MoltenOutputBorder: border of a failed output window
MoltenOutputBorderSuccess = MoltenOutputBorder: border of a successfully run output window
MoltenOutputWin = NormalFloat: the innards of the output window
MoltenOutputWinNC = MoltenOutputWin: a "Non-Current" output window
MoltenOutputFooter = FloatFooter: the "x more lines" text
MoltenCell = CursorLine: applied to code that makes up a cell
MoltenVirtualText = Comment: output that is rendered as virtual text

Autocommands

We provide some User autocommands (see :help User) for further customization. They are:

MoltenInitPre: runs right before MoltenInit initialization happens for a buffer
MoltenInitPost: runs right after MoltenInit initialization happens for a buffer
MoltenDeinitPre: runs right before MoltenDeinit de-initialization happens for a buffer
MoltenDeinitPost: runs right after MoltenDeinit de-initialization happens for a buffer
MoltenKernelReady: runs when a kernel is ready for the first time. data field has the kernel_id

Here is an example of attaching molten specific mappings to the buffer after initialization:

vim.api.nvim_create_autocmd("User", {
  pattern = "MoltenInitPost",
  callback = function()
    vim.keymap.set("v", "<localleader>r", ":<C-u>MoltenEvaluateVisual<CR>gv",
      { desc = "execute visual selection", buffer = true, silent = true })
    -- ... more mappings
  end,
})

Similarly, you could remove these mappings on MoltenDeinitPost

For MoltenKernelReady you can get the kernel id like this:

-- ...
  callback = function(e)
    print("Kernel id: " .. e.data.kernel_id)
  end
-- ...

Functions

Molten exposes some functionality through vim functions. These are mostly for plugin authors and people who want some custom behavior.

MoltenEvaluateRange(start_line, end_line, [start_col, end_col]) - evaluates the code between the given line numbers and column numbers.

ranges are inclusive and the indexing 1 based
columns are optional, when omitted the entire line is captured
passing -1 for end_col will use the last col on the line
passing 0 for all other positions will use the last line/col
The values are used to create extmarks, and the strict option is set to false. See :h nvim_buf_set_extmark() and then options > strict. This means passing 10 when there are only 5 lines in the buffer does result in an error.

-- run lines 1 through 23 (inclusive):
vim.fn.MoltenEvaluateRange(1, 23)

-- run code starting with col 4 on line 1, and ending with the last col on line 3
vim.fn.MoltenEvaluateRange(1, 3, 4, -1)

Additionally, this function can take a kernel_id as the first argument. When a string is given as the first argument, it's assumed to be a kernel_id.

-- run lines 1 through 23 (inclusive) with the python3 kernel
vim.fn.MoltenEvaluateRange("python3", 1, 23)

-- run code starting with col 4 on line 1, and ending with col 20 on line 3 with the R kernel
vim.fn.MoltenEvaluateRange("ir", 1, 3, 4, 20)

When there are multiple kernels attached to the buffer, and this function is called without a kernel_id, the user will be prompted for a kernel with vim.ui.select

Because Molten is a remote plugin, options are loaded and cached at initialization. This avoids making an unnecessary number of RPC calls if we were to fetch configuration values every time we needed to use them. This comes with the trade-off of not being able to update config values on the fly... can you see where this is going.

This function lets you update a configuration value after initialization, and the new value will take effect immediately.

You can specify option names with or without the "molten" prefix.

-- these are the same!
vim.fn.MoltenUpdateOption("auto_open_output", true)
vim.fn.MoltenUpdateOption("molten_auto_open_output", true)

Return a list of the currently running kernels' IDs. Takes one argument, when true, returns only kernels running in the current buffer. Otherwise, returns all running kernel_ids.

vim.fn.MoltenRunningKernels(true) -- list buf local kernel ids
vim.fn.MoltenRunningKernels(false) -- list all kernel ids

Returns a list of kernel names that molten is aware of.

vim.fn.MoltenAvailableKernels()

Takes in a start line, and end line, and a kernel and creates a code cell in the current buffer associated with that kernel. Does not run the code or create/open an output window.

for compatibility reasons, if there is only one active kernel, you do not need to pass the kernel argument

-- Creates a cell from line 5 to line 10 associated with the python3 kernel
vim.fn.MoltenDefineCell(5, 10, 'python3')

Output Chunks

In the Jupyter protocol, most output-related messages provide a dictionary of mime-types which can be used to display the data. Theoretically, a text/plain field (i.e., plain text) is always present, so we (theoretically) always have that fallback.

Here is a list of the currently handled mime-types:

text/plain: Plain text. Shown as text in the output window's buffer.
image/*: Molten attempts to render any image mimetype by sending it to image.nvim. In theory, this means that Molten can handle any image format that image.nvim supports, though I've only tested common formats
- Images are also viewable outside of the terminal with :MoltenImagePopup
application/vnd.plotly.v1+json: A Plotly figure. Rendered into a PNG with Plotly + Kaleido
text/latex: A LaTeX formula. Rendered into a PNG with pnglatex
text/html: via the :MoltenOpenInBrowser command.

This already provides quite a bit of basic functionality, but if you find a use case for a mime-type that isn't currently supported, feel free to open an issue and/or PR!

Thanks

@dccsillag and everyone who has contributed to magma-nvim
@3rd and everyone who has contributed to image.nvim