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README.md

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+# vim-jupycent
+
+Plugin for editing [Jupyter notebook][1] (ipynb) files via the [jupytext][2]
+percent format.
+
+[jupytext.vim][3] is an excellent plugin, but it loads the result of the
+jupytext conversion into the ipynb buffer, which causes issues with other
+plugins for version control (e.g., gitgutter) and linting (e.g., coc.nvim).
+[jupytext.vim][3] is also a more flexible wrapper of jupytext, whereas
+vim-jupycent only converts to the python percent format, and adds some
+highlighting and folding based on this format.
+
+## Installation
+
+1. Make sure that you have the `jupytext` CLI program installed (`pip install jupytext`).
+2. Install this plugin with your favourite method, like vim-plug (`Plug 'gabenespoli/vim-jupycent'`).
+
+## Usage
+
+When you open a Jupyter Notebook (`*.ipynb`) file, it is automatically
+converted from json to markdown or python through the [`jupytext` utility][2],
+and the result is loaded into the buffer. Upon saving, the `ipynb` file is
+updated with any modifications.
+
+In more detail, opening a file `notebook.ipynb` in vim will create a temporary
+file  `notebook.py`. This file is the result of calling e.g.
+
+    jupytext --to=py:percent --output notebook.md notebook.ipynb
+
+The file `notebook.py` is opened, and the original `notebook.ipynb` is wiped
+from vim. When saving the buffer, its contents is first written to
+`notebook.py`, and then the original `notebook.ipynb` is updated with a call to
+
+    jupytext --from=py:percent --to=ipynb --update --output notebook.ipynb notebook.py
+
+The `--update` flag ensures the output for any cell whose corresponding input
+in `notebook.py` is unchanged will be preserved.
+
+On closing the buffer, the temporary `notebook.py` will be deleted. If
+`notebook.py` already existed when opening `notebook.ipynb`, the existing file
+will be used (instead of being generated by `jupytext`), and it will be
+preserved when closing the buffer.
+
+## Configuration
+
+The plugin has the following settings. If you want to override the default values shown below, you can define the corresponding variables in your `~/.vimrc`.
+
+*   `let g:jupytext_enable = 1`
+
+    You may disable the automatic conversion of `ipynb` files (i.e., deactivate this plugin) by setting this to 0.
+
+*   `let g:jupytext_command = 'jupytext'`
+
+    The CLI `jupytext` command to use. You may include the full path to point to a specific `jupytext` executable not in your default `$PATH`.
+
+*  `let g:jupytext_to_ipynb_opts = '--to=ipynb --update'`
+
+   Command line options for the conversion from `g:jupytext_fmt` back to the notebook format
+
+## Acknowledgements
+
+This plugin takes some inspiration, code, and documentation from [jupytext.vim][3]. vim-jupycent is basically a fork of [jupytext.vim][3], but is probably too different to call it a fork.
+
+[1]: http://jupyter.org
+[2]: https://github.com/mwouts/jupytext
+[3]: https://github.com/goerz/jupytext.vim

plugin/jupycent.vim

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+if exists("loaded_jupycent")
+    finish
+endif
+
+if !exists('g:jupycent_command')
+    let g:jupycent_command = 'jupytext'
+endif
+
+if !exists('g:jupycent_enable')
+    let g:jupycent_enable = 1
+endif
+
+if !exists('g:jupycent_to_ipynb_opts')
+    let g:jupycent_to_ipynb_opts = '--to=ipynb --update'
+endif
+
+if !g:jupycent_enable
+    finish
+endif
+
+augroup jupycent_ipynb
+    au!
+    autocmd BufReadPost *.ipynb call s:read_from_ipynb()
+augroup END
+
+function! s:read_from_ipynb()
+  if expand("<afile>:e") != "ipynb"
+    echo "Not an ipynb file."
+    return
+  endif
+  let l:filename = expand("%:p")
+  let l:jupycent_file = fnamemodify(l:filename, ":r") . ".py"
+  let l:jupycent_file_exists = filereadable(l:jupycent_file)
+  if !filereadable(l:jupycent_file)
+    let l:output = system(g:jupycent_command . " --to=py:percent "
+          \ . "--output=" . shellescape(l:jupycent_file) . " "
+          \ . shellescape(l:filename))
+  endif
+
+  " open the jupytext py:percent file, wipe the ipynb file
+  let l:bufnr = bufnr("%")
+  execute "edit " . l:jupycent_file
+  execute "bwipeout" . l:bufnr
+
+  " set properties of the jupycent file buffer
+  let b:jupycent_ipynb_file = l:filename
+  set filetype=python
+  setlocal foldmethod=expr
+  setlocal foldexpr=JupycentFold(v:lnum)
+  setlocal foldtext=getline(v:foldstart+1)
+  syntax match JupycentCell /^#\ %%/
+  hi link JupycentCell FoldColumn
+  execute "autocmd jupycent_ipynb BufWritePost,FileWritePost <buffer> call s:write_to_ipynb()"
+  if !l:jupycent_file_exists
+    execute "autocmd jupycent_ipynb BufUnload <buffer> call s:cleanup()"
+  endif
+endfunction
+
+function! s:write_to_ipynb() abort
+  if !exists("b:jupycent_ipynb_file")
+    echo "Not a jupycent py file."
+    return
+  endif
+  let l:jupycent_file = expand("<afile>:p")
+  let l:output = system(g:jupycent_command . " --from=py:percent "
+        \ . g:jupycent_to_ipynb_opts . " "
+        \ . "--output " . shellescape(b:jupycent_ipynb_file) . " "
+        \ . shellescape(l:jupycent_file))
+  echo b:jupycent_ipynb_file . " updated."
+endfunction
+
+function! s:cleanup()
+  if !exists("b:jupycent_ipynb_file")
+    echo "Not a jupycent py file."
+    return
+  endif
+  call delete(expand("<afile>:p"))
+endfunction
+
+function! JupycentFold(lnum)
+  let l:line = getline(a:lnum) 
+  if a:lnum <= 2 && l:line =~# '^#\ ---$'
+    return '>1'
+  elseif l:line =~# '^#\ %%$'
+    return '>1'
+  elseif l:line =~# '^#\ %% [markdown]$'
+    return '>1'
+  else
+    return '='
+  endif
+endfunction
+
+let loaded_jupycent = 1