Add exporting single notebook outside nbdev project

To export a notebook to a .py file outside an nbdev project:
```
import nbdev
nbdev.export.nb_export('./example.ipynb', '.', solo_nb=True)
```

Key change: added `solo_nb` arg that propagates the intent through
functionality involved in exported module generation.

nbdev/config.py

@@ -249,12 +249,12 @@ def add_init(path=None):
     if get_config().get('put_version_in_init', True): update_version(path)
 
 # %% ../nbs/api/01_config.ipynb
-def write_cells(cells, hdr, file, offset=0, cell_number=True):
+def write_cells(cells, hdr, file, offset=0, cell_number=True, solo_nb=False):
     "Write `cells` to `file` along with header `hdr` starting at index `offset` (mainly for nbdev internal use)."
     for cell in cells:
         if cell.cell_type=='code' and cell.source.strip():
             idx = f" {cell.idx_+offset}" if cell_number else ""
-            file.write(f'\n\n{hdr}{idx}\n{cell.source}')
+            file.write(f'\n\n{hdr}{idx}\n{cell.source}') if not solo_nb else file.write(f'\n\n{cell.source}')
 
 # %% ../nbs/api/01_config.ipynb
 def _basic_export_nb(fname, name, dest=None):

nbdev/export.py

@@ -73,6 +73,7 @@ def nb_export(nbname:str,        # Filename of notebook
               name:str=None,     # Name of python script {name}.py to create.
               mod_maker=ModuleMaker,
               debug:bool=False,  # Debug mode
+              solo_nb:bool=False # Export single notebook outside of an nbdev project.
              ):
     "Create module(s) from notebook"
     if lib_path is None: lib_path = get_config().lib_path if is_nbdev() else '.'
@@ -88,5 +89,5 @@ def nb_export(nbname:str,        # Filename of notebook
                      "Note nbdev2 no longer supports nbdev1 syntax. Run `nbdev_migrate` to upgrade.\n"
                      "See https://nbdev.fast.ai/getting_started.html for more information.")
                 return
-            mm = mod_maker(dest=lib_path, name=nm, nb_path=nbname, is_new=bool(name) or mod=='#')
+            mm = mod_maker(dest=lib_path, name=nm, nb_path=nbname, is_new=bool(name) or mod=='#', solo_nb=solo_nb)
             mm.make(cells, all_cells, lib_path=lib_path)

nbdev/maker.py

@@ -63,7 +63,7 @@ def update_var(varname, func, fn=None, code=None):
 # %% ../nbs/api/02_maker.ipynb
 class ModuleMaker:
     "Helper class to create exported library from notebook source cells"
-    def __init__(self, dest, name, nb_path, is_new=True, parse=True):
+    def __init__(self, dest, name, nb_path, is_new=True, parse=True, solo_nb=False):
         dest,nb_path = Path(dest),Path(nb_path)
         store_attr()
         self.fname = dest/(name.replace('.','/') + ".py")
@@ -208,8 +208,8 @@ def make(self:ModuleMaker, cells, all_cells=None, lib_path=None):
         f.write(_retr_mdoc(cells))
         f.write(f"# AUTOGENERATED! DO NOT EDIT! File to edit: {self.dest2nb}.")
         if last_future > 0: write_cells(cells[:last_future], self.hdr, f)
-        if self.parse: f.write(f"\n\n# %% auto 0\n__all__ = {all_str}")
-        write_cells(cells[last_future:], self.hdr, f, cell_number=get_config().cell_number)
+        if self.parse and not self.solo_nb: f.write(f"\n\n# %% auto 0\n__all__ = {all_str}")
+        write_cells(cells[last_future:], self.hdr, f, cell_number=get_config().cell_number, solo_nb=self.solo_nb)
         f.write('\n')
 
 # %% ../nbs/api/02_maker.ipynb

nbs/api/01_config.ipynb

@@ -735,12 +735,12 @@
    "outputs": [],
    "source": [
     "#|export\n",
-    "def write_cells(cells, hdr, file, offset=0, cell_number=True):\n",
+    "def write_cells(cells, hdr, file, offset=0, cell_number=True, solo_nb=False):\n",
     "    \"Write `cells` to `file` along with header `hdr` starting at index `offset` (mainly for nbdev internal use).\"\n",
     "    for cell in cells:\n",
     "        if cell.cell_type=='code' and cell.source.strip():\n",
     "            idx = f\" {cell.idx_+offset}\" if cell_number else \"\"\n",
-    "            file.write(f'\\n\\n{hdr}{idx}\\n{cell.source}')"
+    "            file.write(f'\\n\\n{hdr}{idx}\\n{cell.source}') if not solo_nb else file.write(f'\\n\\n{cell.source}')"
    ]
   },
   {

nbs/api/02_maker.ipynb

@@ -201,7 +201,7 @@
     "#|export\n",
     "class ModuleMaker:\n",
     "    \"Helper class to create exported library from notebook source cells\"\n",
-    "    def __init__(self, dest, name, nb_path, is_new=True, parse=True):\n",
+    "    def __init__(self, dest, name, nb_path, is_new=True, parse=True, solo_nb=False):\n",
     "        dest,nb_path = Path(dest),Path(nb_path)\n",
     "        store_attr()\n",
     "        self.fname = dest/(name.replace('.','/') + \".py\")\n",
@@ -518,8 +518,8 @@
     "        f.write(_retr_mdoc(cells))\n",
     "        f.write(f\"# AUTOGENERATED! DO NOT EDIT! File to edit: {self.dest2nb}.\")\n",
     "        if last_future > 0: write_cells(cells[:last_future], self.hdr, f)\n",
-    "        if self.parse: f.write(f\"\\n\\n# %% auto 0\\n__all__ = {all_str}\")\n",
-    "        write_cells(cells[last_future:], self.hdr, f, cell_number=get_config().cell_number)\n",
+    "        if self.parse and not self.solo_nb: f.write(f\"\\n\\n# %% auto 0\\n__all__ = {all_str}\")\n",
+    "        write_cells(cells[last_future:], self.hdr, f, cell_number=get_config().cell_number, solo_nb=self.solo_nb)\n",
     "        f.write('\\n')"
    ]
   },

nbs/api/04_export.ipynb

@@ -244,6 +244,7 @@
     "              name:str=None,     # Name of python script {name}.py to create.\n",
     "              mod_maker=ModuleMaker,\n",
     "              debug:bool=False,  # Debug mode\n",
+    "              solo_nb:bool=False # Export single notebook outside of an nbdev project.\n",
     "             ):\n",
     "    \"Create module(s) from notebook\"\n",
     "    if lib_path is None: lib_path = get_config().lib_path if is_nbdev() else '.'\n",
@@ -259,7 +260,7 @@
     "                     \"Note nbdev2 no longer supports nbdev1 syntax. Run `nbdev_migrate` to upgrade.\\n\"\n",
     "                     \"See https://nbdev.fast.ai/getting_started.html for more information.\")\n",
     "                return\n",
-    "            mm = mod_maker(dest=lib_path, name=nm, nb_path=nbname, is_new=bool(name) or mod=='#')\n",
+    "            mm = mod_maker(dest=lib_path, name=nm, nb_path=nbname, is_new=bool(name) or mod=='#', solo_nb=solo_nb)\n",
     "            mm.make(cells, all_cells, lib_path=lib_path)"
    ]
   },