Problem with interactive use of declarative syntax

bug.ipynb

{
 "cells": [
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "12bd2b79-5072-440a-ab46-21d84404b5a0",
   "metadata": {},
   "outputs": [],
   "source": [
    "from datetime import datetime, timedelta\n",
    "from metpy.io import metar\n",
    "from metpy.plots.declarative import PlotObs, MapPanel, PanelContainer"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "97173674-17d8-44cb-8bba-edc1b14fd260",
   "metadata": {},
   "outputs": [],
   "source": [
    "def top_of_hr():\n",
    "    now = datetime.utcnow()\n",
    "    ymd = now.strftime('%y%m%d')\n",
    "    hr = now.strftime('%H')\n",
    "    dt_top = now.replace(microsecond=0, second=0, minute=0)\n",
    "    return ymd, hr, dt_top\n",
    "\n",
    "ymd, hr, plot_time = top_of_hr()"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "2394a54d-a475-4ae9-90bf-ce23de9fddb9",
   "metadata": {},
   "outputs": [],
   "source": [
    "# Replace with appropriate path on your system\n",
    "sfc_file = '/nfs/wxdata1/ldmdata/weather/sfc/' + ymd + hr + '_sao.txt'"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "103ef608-e4f9-4984-9d11-23754e175e67",
   "metadata": {},
   "outputs": [],
   "source": [
    "sfc_obs = metar.parse_metar_file(sfc_file)\n",
    "\n",
    "obs = PlotObs()\n",
    "obs.data = sfc_obs\n",
    "obs.time = plot_time\n",
    "obs.time_window = timedelta(minutes=15)\n",
    "obs.level = None\n",
    "obs.fields = ['cloud_coverage', 'air_temperature', 'dew_point_temperature',\n",
    "              'air_pressure_at_sea_level', 'current_wx1_symbol']\n",
    "obs.plot_units = [None, 'degF', 'degF', None, None]\n",
    "obs.locations = ['C', 'NW', 'SW', 'NE', 'W']\n",
    "obs.formats = ['sky_cover', None, None, lambda p: format(p * 10, '.0f')[-3:],\n",
    "               'current_weather']\n",
    "obs.reduce_points = 2\n",
    "obs.vector_field = ['eastward_wind', 'northward_wind']"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "037585c0-bfbf-4c58-bb6e-61d656c1df96",
   "metadata": {},
   "outputs": [],
   "source": [
    "panel = MapPanel()\n",
    "panel.layout = (1, 1, 1)\n",
    "panel.projection = 'lcc'\n",
    "panel.area = 'us'\n",
    "panel.layers = ['countries','states']\n",
    "#panel.layers = ['borders','states']\n",
    "panel.title = f'Surface plot for {plot_time}'\n",
    "panel.plots = [obs]"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "2f89d215-18c3-44c5-bae4-216df4dc00fb",
   "metadata": {},
   "outputs": [],
   "source": [
    "pc = PanelContainer()\n",
    "pc.size = (10, 10)\n",
    "pc.panels = [panel]\n",
    "pc.show()"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "214da4a4-75ce-458e-8fcc-ddfafd45ba77",
   "metadata": {},
   "source": [
    "Running this code as is generates:\n",
    "```\n",
    "AttributeError: module 'metpy.plots.cartopy_utils' has no attribute 'COUNTRIES'\n",
    "```\n",
    "\n",
    "If I then fix the code by commenting out the bad definition of `panel.layers` in cell 5 and uncommenting out the good definition, and rerun cell 5, I get this error:\n",
    "```\n",
    "AttributeError: 'NoneType' object has no attribute 'figure'\n",
    "```\n",
    "\n",
    "However, if I \"Restart Kernel and Run All Cells\", the fixed code works as it should."
   ]
  }
 ],
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