Fix backend tutorial build (xarray-contrib#111)

Author: dcherian

advanced/backends/1.Backend_without_Lazy_Loading.ipynb

@@ -17,20 +17,20 @@
     "## BackendEntrypoint\n",
     "Implement a subclass of `BackendEntrypoint` that expose a method `open_dataset`:\n",
     "\n",
-    "   ```python\n",
-    "    from xarray.backends import BackendEntrypoint\n",
+    "```python\n",
+    "from xarray.backends import BackendEntrypoint\n",
+    "\n",
+    "class MyBackendEntrypoint(BackendEntrypoint):\n",
+    "    def open_dataset(\n",
+    "        self,\n",
+    "        filename_or_obj,\n",
+    "        *,\n",
+    "        drop_variables=None,\n",
+    "    ):\n",
     "\n",
-    "    class MyBackendEntrypoint(BackendEntrypoint):\n",
-    "        def open_dataset(\n",
-    "            self,\n",
-    "            filename_or_obj,\n",
-    "            *,\n",
-    "            drop_variables=None,\n",
-    "        ):\n",
-    "            \n",
-    "            return my_open_dataset(filename_or_obj, drop_variables=drop_variables)\n",
+    "        return my_open_dataset(filename_or_obj, drop_variables=drop_variables)\n",
     "\n",
-    "   ```"
+    "```"
    ]
   },
   {
@@ -41,20 +41,18 @@
     "Declare this class as an external plugin in your `setup.py`:\n",
     "\n",
     "```python\n",
-    "    setuptools.setup(\n",
-    "        ...\n",
-    "        entry_points={\n",
-    "            'xarray.backends': ['engine_name=package.module:my_backendentrypoint'],\n",
-    "        },\n",
-    "    )\n",
-    "\n",
+    "setuptools.setup(\n",
+    "    ...\n",
+    "    entry_points={\n",
+    "        'xarray.backends': ['engine_name=package.module:my_backendentrypoint'],\n",
+    "    },\n",
+    ")\n",
     "```\n",
     "or pass it in `xr.open_dataset`:\n",
     "\n",
     "```python\n",
-    "    xr.open_dataset(..., engine=MyBackendEntrypoint)\n",
-    "```\n",
-    "<br/>"
+    "xr.open_dataset(..., engine=MyBackendEntrypoint)\n",
+    "```"
    ]
   },
   {

advanced/backends/2.Backend_with_Lazy_Loading.ipynb

@@ -25,6 +25,41 @@
     "<br/>"
    ]
   },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Create sample files"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "import os\n",
+    "\n",
+    "import dask\n",
+    "import numpy as np\n",
+    "import xarray as xr"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "arr = np.arange(30000000, dtype=np.int64)\n",
+    "with open(\"foo.bin\", \"w\") as f:\n",
+    "    arr.tofile(f)\n",
+    "\n",
+    "arr = np.arange(30000000, dtype=np.float64)\n",
+    "with open(\"foo_float.bin\", \"w\") as f:\n",
+    "    arr.tofile(f)"
+   ]
+  },
   {
    "cell_type": "markdown",
    "metadata": {},
@@ -54,13 +89,6 @@
    "metadata": {},
    "outputs": [],
    "source": [
-    "import os\n",
-    "\n",
-    "import dask\n",
-    "import numpy as np\n",
-    "import xarray as xr\n",
-    "\n",
-    "\n",
     "class BinaryBackendArray(xr.backends.BackendArray):\n",
     "    def __init__(\n",
     "        self,\n",