Bad rendering of stream outputs when executing through nbconvert

[knuesel]

When a notebook is executed by nbconvert, some stream outputs are split into many small outputs, causing bad rendering.

For example the notebook test.ipynb contains the following cells:

help

a = 1;
whos

The help command is included here as an example where the stream output works correctly. The problem is with the second cell. When executed in Jupyterlab it renders correctly:

Variables visible from the current scope:

variables in scope: top scope

  Attr   Name        Size                     Bytes  Class
  ====   ====        ====                     =====  ===== 
         a           1x1                          8  double

Total is 1 element using 8 bytes

and the output is stored correctly in the ipynb JSON:

   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Variables visible from the current scope:\n",
      "\n",
      "variables in scope: top scope\n",
      "\n",
      "  Attr   Name        Size                     Bytes  Class\n",
      "  ====   ====        ====                     =====  ===== \n",
      "         a           1x1                          8  double\n",
      "\n",
      "Total is 1 element using 8 bytes\n",
      "\n"
     ]
    }
   ],

and calling nbconvert --to html test.ipynb gives a good-looking HTML file: test.html. Screenshot:

However when calling jupyter-nbconvert --to html test.ipynb --execute to execute the notebook while converting, the text output is badly formatted: test.html. Screenshot:

Running jupyter-nbconvert --to notebook test.ipynb --execute to see the ipynb JSON for the execution result shows that the stream output is stored as a large number of small outputs (almost one output per word or blank):

JSON of stream output for "whos" command

   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Variables visible from the current scope:\n"
     ]
    },
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "\n",
      "variables in scope: "
     ]
    },
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "top scope"
     ]
    },
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "\n",
      "\n"
     ]
    },
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "  "
     ]
    },
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Attr  "
     ]
    },
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      " "
     ]
    },
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Name  "
     ]
    },
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      " "
     ]
    },
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "     "
     ]
    },
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Size"
     ]
    },
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "            "
     ]
    },
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "  "
     ]
    },
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "       Bytes"
     ]
    },
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "  "
     ]
    },
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Class"
     ]
    },
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "\n"
     ]
    },
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "  ====   ====        ====                     =====  ===== "
     ]
    },
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "\n"
     ]
    },
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "  "
     ]
    },
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "      "
     ]
    },
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      " "
     ]
    },
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "a     "
     ]
    },
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      " "
     ]
    },
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "     "
     ]
    },
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "1x1"
     ]
    },
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "             "
     ]
    },
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "  "
     ]
    },
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "           8"
     ]
    },
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "  "
     ]
    },
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "double"
     ]
    },
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "\n"
     ]
    },
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "\n",
      "Total is "
     ]
    },
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "1"
     ]
    },
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      " element"
     ]
    },
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      " using "
     ]
    },
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "8"
     ]
    },
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      " bytes"
     ]
    },
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "\n"
     ]
    },
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "\n"
     ]
    }
   ],
   "source": [
    "a = 1;\n",
    "whos"
   ]
  }
 ],

Full JSON file: test.nbconvert.ipynb