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   "source": [
    "# ... add an affix-function to a standard name table during runtime?\n",
    "If you are using the [standard name convention](../userguide/convention/index.rst), you are familiar with transformation functions like \"derivative_of_\\<SN1\\>_wrt_\\<SN2\\>\" or \"square_of_\\<SN\\>\".\n",
    "\n",
    "Now, you want to add your custom transformation function without changing the package code. Say, you want to add the transformation \"maximum_of_<StdName>\", referring to the maximum value of your data.\n",
    "\n",
    "Here is the current state, which fails as expected:"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 1,
   "id": "791af21d-0c99-4d0b-bb0b-b5f59ecb1c8c",
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "\"maximum_of_pressure\" not found in Standard Name Table \"Test\".\n"
     ]
    }
   ],
   "source": [
    "import h5rdmtoolbox as h5tbx\n",
    "from h5rdmtoolbox.convention.standard_names.transformation import Transformation\n",
    "from h5rdmtoolbox.convention.standard_names import StandardName\n",
    "\n",
    "snt = h5tbx.convention.standard_names.StandardNameTable.from_zenodo(doi_or_recid=10428795)\n",
    "\n",
    "# check if the problem really exists:\n",
    "try:\n",
    "    snt['maximum_of_pressure']\n",
    "except h5tbx.errors.StandardNameError as e:\n",
    "    print(e)"
   ]
  },
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   "cell_type": "markdown",
   "id": "04b2c358-783c-4e6b-8d56-a1ffee7fdf70",
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   "source": [
    "## Implementing a new transformation function\n",
    "\n",
    "We need to do two things:\n",
    " 1. write a `function` which takes a regex result and generates the new standard name\n",
    " 2. init a `Transformation` object which performs the regex match\n",
    "\n",
    "The respective regex pattern to the above is `^maximum_of_(.*)$`.\n",
    "\n",
    "The respective function is implemented in the following. It takes the result from a `re.match()` call and the standard name table object. The function then constructs a new standard name and returns it. Even if the regex match succeeded, it is still possible, that the function raises an error because the base standard_name may not exist."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 2,
   "id": "dc0db89c-c3b9-4c41-87dc-6a5ae91fc356",
   "metadata": {},
   "outputs": [],
   "source": [
    "def maximum_of(match, snt):\n",
    "    # match is the result of `re.match(`^maximum_of_(.*)$, <user_input_value>)`\n",
    "    groups = match.groups()\n",
    "    assert len(groups) == 1\n",
    "    sn = snt[groups[0]]\n",
    "    new_description = f\"Maximum of {sn.name}. {sn.description}\"\n",
    "    return StandardName(match.string, sn.units, new_description)"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "b634d764-aeb9-4dde-bb00-7cf59941c15f",
   "metadata": {},
   "source": [
    "The actual transformation is managed by the class `Transformation`. It takes the above defined function and the respective regex pattern:"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 3,
   "id": "e10d2b65-b6ea-42ce-909d-a375a0ba71ed",
   "metadata": {},
   "outputs": [],
   "source": [
    "max_of = Transformation(r\"^maximum_of_(.*)$\", maximum_of)"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "70de8f86-6a83-4b70-9fa6-b1f20fecaa98",
   "metadata": {},
   "source": [
    "We can already check if the pattern matching works:"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 4,
   "id": "9f9d5fa2-9dfa-46ff-bc9b-8b9db8f5870a",
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "True"
      ]
     },
     "execution_count": 4,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "max_of.match('maximum_static_pressure') is None"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 5,
   "id": "f54490f6-0272-4483-86f2-71fba12207c0",
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "False"
      ]
     },
     "execution_count": 5,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "max_of.match('maximum_of_static_pressure') is None"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "949bac12-f381-43a2-adfb-44848dafb559",
   "metadata": {},
   "source": [
    "## Add it to an existing standard name table during runtime:"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 6,
   "id": "a5ae8c3a-3115-400f-bd02-3d75578c707a",
   "metadata": {},
   "outputs": [],
   "source": [
    "snt.add_transformation(max_of)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 7,
   "id": "835d7ccb-afca-429a-a5f1-38b8a18e4230",
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    {
     "data": {
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       "<ul style=\"list-style-type: none;\" class=\"h5grp-sections\">\n",
       "    <li>\n",
       "        <input id=\"group-maximum_of_static_pressure6876410300\" type=\"checkbox\" checked>\n",
       "        <label style=\"font-weight: bold\" for=\"group-maximum_of_static_pressure6876410300\">\n",
       "        maximum_of_static_pressure</label>\n",
       "        <ul class=\"h5tb-attr-list\">\n",
       "           <li style=\"list-style-type: none; font-style: italic\">units : Pa</li>           <li style=\"list-style-type: none; font-style: italic\">description : Maximum of static_pressure. Static pressure refers to the force per unit area exerted by a fluid. Pressure is a scalar quantity.</li>      </il>\n",
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       "<StandardName: \"maximum_of_static_pressure\" [Pa] Maximum of static_pressure. Static pressure refers to the force per unit area exerted by a fluid. Pressure is a scalar quantity.>"
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    "snt['maximum_of_static_pressure']"
   ]
  },
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   "cell_type": "code",
   "execution_count": 8,
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       "True"
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     "execution_count": 8,
     "metadata": {},
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   "source": [
    "snt.transformations[-1] == max_of"
   ]
  },
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   "cell_type": "code",
   "execution_count": null,
   "id": "18d18150-ab33-480f-9d9e-0c02a26e9aa9",
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