Iterating through the properties of arcpy objects

iterating_arcpy_object.ipynb

{
 "cells": [
  {
   "cell_type": "code",
   "execution_count": 1,
   "metadata": {
    "collapsed": true
   },
   "outputs": [],
   "source": [
    "import arcpy"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Many of ArcGIS users need to iterate the propeties of `arcpy` objects, such as `Describe` objects or `Layer` objects. The purpose of iterating is to get all the information available either for reporting purposes or during the troubleshooting time. Speaking of `Layer` objects, let's see what Python code is needed for iterating through their properties.\n",
    "\n",
    "First, we need to obtain the `Layer` object. This is how we can get hands at the obj which represents the `Layer` object. "
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 2,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "data": {
      "text/plain": [
       "<map layer u'GridLayer'>"
      ]
     },
     "execution_count": 2,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "import arcpy\n",
    "\n",
    "mxd_path = r'C:\\GIS\\introspect.mxd'\n",
    "mxd = arcpy.mapping.MapDocument(mxd_path)\n",
    "df = arcpy.mapping.ListDataFrames(mxd, \"Layers\")[0]\n",
    "obj = arcpy.mapping.ListLayers(mxd, \"GridLayer\", df)[0]\n",
    "obj"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 3,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "data": {
      "text/plain": [
       "True"
      ]
     },
     "execution_count": 3,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "obj.isFeatureLayer"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "A naïve way to list all the properties of this object is to do something like this:"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 4,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "data source -- C:\\GIS\\Temp\\test.gdb\\GridFeatures\n",
      "dataset name -- GridFeatures\n",
      "workspace path -- C:\\GIS\\Temp\\test.gdb\n"
     ]
    }
   ],
   "source": [
    "print \"data source --\", obj.dataSource\n",
    "print \"dataset name --\", obj.datasetName\n",
    "print \"workspace path --\", obj.workspacePath"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "This could of course be shortened a bit to something like this with the help of `getattr()` method ([help link](https://docs.python.org/2/reference/datamodel.html#object.__getattr__)):"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 5,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "dataSource C:\\GIS\\Temp\\test.gdb\\GridFeatures\n",
      "datasetName GridFeatures\n",
      "workspacePath C:\\GIS\\Temp\\test.gdb\n"
     ]
    }
   ],
   "source": [
    "props = ['dataSource','datasetName','workspacePath']\n",
    "for p in props:\n",
    "    print p, getattr(obj,p)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "This implies, however, that you still need to create and maintain the list of available properties for each type of object (`Layer` object has different kind of properties than the `Describe` object).\n",
    "\n",
    "A more elegant solution to this is to access all the properties of an object using the Python built-in `dir()` command.  `dir(obj)` will return all the attributes and methods that an instance of the class has. This includes private methods and attributes which could be ignored as they are not `arcpy` specific."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 6,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "['brightness', 'contrast', 'credits', 'dataSource', 'datasetName', 'definitionQuery', 'description', 'findAndReplaceWorkspacePath', 'getExtent', 'getSelectedExtent', 'getSelectionSet', 'isBroken', 'isFeatureLayer', 'isGroupLayer', 'isNetworkAnalystLayer', 'isRasterLayer', 'isRasterizingLayer', 'isServiceLayer', 'labelClasses', 'longName', 'maxScale', 'minScale', 'name', 'replaceDataSource', 'save', 'saveACopy', 'serviceProperties', 'setSelectionSet', 'showLabels', 'supports', 'symbology', 'symbologyType', 'time', 'transparency', 'updateLayerFromJSON', 'visible', 'workspacePath']\n"
     ]
    }
   ],
   "source": [
    "props = [prop for prop in [prop for prop in dir(obj) if '_' not in prop]]\n",
    "print props"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "This is great! We can probably just use the `getattr()` method now and list all the values of every property this `Layer` object has."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 7,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "ename": "ValueError",
     "evalue": "LayerObject: Layer does not support brightness",
     "output_type": "error",
     "traceback": [
      "\u001b[1;31m---------------------------------------------------------------------------\u001b[0m",
      "\u001b[1;31mValueError\u001b[0m                                Traceback (most recent call last)",
      "\u001b[1;32m<ipython-input-7-7adcfb79fb31>\u001b[0m in \u001b[0;36m<module>\u001b[1;34m()\u001b[0m\n\u001b[0;32m      1\u001b[0m \u001b[1;32mfor\u001b[0m \u001b[0mprop\u001b[0m \u001b[1;32min\u001b[0m \u001b[0mprops\u001b[0m\u001b[1;33m:\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[1;32m----> 2\u001b[1;33m     \u001b[1;32mprint\u001b[0m \u001b[0mgetattr\u001b[0m\u001b[1;33m(\u001b[0m\u001b[0mobj\u001b[0m\u001b[1;33m,\u001b[0m\u001b[0mprop\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0m",
      "\u001b[1;31mValueError\u001b[0m: LayerObject: Layer does not support brightness"
     ]
    }
   ],
   "source": [
    "for prop in props:\n",
    "    print getattr(obj,prop)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Not so fast. Not all properties are supported by this particular map layer of `Feature Layer` type. `Raster Layer` type, for instance, would support other properties, so we have to distinguish between those. There is `supports()` method that does just that:"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 8,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "False\n",
      "True\n"
     ]
    }
   ],
   "source": [
    "print obj.supports('brightness')\n",
    "print obj.supports('transparency')"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "OK, let's check then whether a property is supported for this type of map layer:"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 9,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "credits \n",
      "dataSource C:\\GIS\\Temp\\test.gdb\\GridFeatures\n",
      "datasetName GridFeatures\n",
      "definitionQuery \n",
      "description \n"
     ]
    },
    {
     "ename": "ValueError",
     "evalue": "Invalid value for layer_property: 'FINDANDREPLACEWORKSPACEPATH' (choices are: ['CREDITS', 'DATASETNAME', 'WORKSPACEPATH', 'DESCRIPTION', 'BRIGHTNESS', 'SHOWLABELS', 'LONGNAME', 'MAXSCALE', 'SYMBOLOGY', 'SYMBOLOGYTYPE', 'SERVICEPROPERTIES', 'VISIBLE', 'DEFINITIONQUERY', 'DATASOURCE', 'TRANSPARENCY', 'TIME', 'MINSCALE', 'LABELCLASSES', 'CONTRAST', 'NAME'])",
     "output_type": "error",
     "traceback": [
      "\u001b[1;31m---------------------------------------------------------------------------\u001b[0m",
      "\u001b[1;31mValueError\u001b[0m                                Traceback (most recent call last)",
      "\u001b[1;32m<ipython-input-9-4ef8a62e6fa7>\u001b[0m in \u001b[0;36m<module>\u001b[1;34m()\u001b[0m\n\u001b[0;32m      1\u001b[0m \u001b[1;32mfor\u001b[0m \u001b[0mprop\u001b[0m \u001b[1;32min\u001b[0m \u001b[0mprops\u001b[0m\u001b[1;33m:\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[1;32m----> 2\u001b[1;33m     \u001b[1;32mif\u001b[0m \u001b[0mobj\u001b[0m\u001b[1;33m.\u001b[0m\u001b[0msupports\u001b[0m\u001b[1;33m(\u001b[0m\u001b[0mprop\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m:\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0m\u001b[0;32m      3\u001b[0m         \u001b[1;32mprint\u001b[0m \u001b[0mprop\u001b[0m\u001b[1;33m,\u001b[0m \u001b[0mgetattr\u001b[0m\u001b[1;33m(\u001b[0m\u001b[0mobj\u001b[0m\u001b[1;33m,\u001b[0m\u001b[0mprop\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n",
      "\u001b[1;31mValueError\u001b[0m: Invalid value for layer_property: 'FINDANDREPLACEWORKSPACEPATH' (choices are: ['CREDITS', 'DATASETNAME', 'WORKSPACEPATH', 'DESCRIPTION', 'BRIGHTNESS', 'SHOWLABELS', 'LONGNAME', 'MAXSCALE', 'SYMBOLOGY', 'SYMBOLOGYTYPE', 'SERVICEPROPERTIES', 'VISIBLE', 'DEFINITIONQUERY', 'DATASOURCE', 'TRANSPARENCY', 'TIME', 'MINSCALE', 'LABELCLASSES', 'CONTRAST', 'NAME'])"
     ]
    }
   ],
   "source": [
    "for prop in props:\n",
    "    if obj.supports(prop):\n",
    "        print prop, getattr(obj,prop)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Hm. Apparently, you cannot throw any string as an input argument for the `supports()` method. In this particular case, we are trying to check whether this layer supports `findAndReplaceWorkspacePath` property. Well, this is actually a method (i.e., a function), not a property. \n",
    "\n",
    "As we are not interested in methods, we have to filter them out of our `props` list. This can be done using the `callable()` function ([help link](https://docs.python.org/2/library/functions.html#callable)). "
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 10,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "True\n",
      "False\n"
     ]
    }
   ],
   "source": [
    "print callable(getattr(obj,'getExtent'))\n",
    "print callable(getattr(obj,'datasetName'))"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 11,
   "metadata": {
    "collapsed": false,
    "scrolled": true
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "credits \n",
      "dataSource C:\\GIS\\Temp\\test.gdb\\GridFeatures\n",
      "datasetName GridFeatures\n",
      "definitionQuery \n",
      "description \n"
     ]
    },
    {
     "ename": "ValueError",
     "evalue": "Invalid value for layer_property: 'FINDANDREPLACEWORKSPACEPATH' (choices are: ['CREDITS', 'DATASETNAME', 'WORKSPACEPATH', 'DESCRIPTION', 'BRIGHTNESS', 'SHOWLABELS', 'LONGNAME', 'MAXSCALE', 'SYMBOLOGY', 'SYMBOLOGYTYPE', 'SERVICEPROPERTIES', 'VISIBLE', 'DEFINITIONQUERY', 'DATASOURCE', 'TRANSPARENCY', 'TIME', 'MINSCALE', 'LABELCLASSES', 'CONTRAST', 'NAME'])",
     "output_type": "error",
     "traceback": [
      "\u001b[1;31m---------------------------------------------------------------------------\u001b[0m",
      "\u001b[1;31mValueError\u001b[0m                                Traceback (most recent call last)",
      "\u001b[1;32m<ipython-input-11-b1452789c1be>\u001b[0m in \u001b[0;36m<module>\u001b[1;34m()\u001b[0m\n\u001b[0;32m      1\u001b[0m \u001b[1;32mfor\u001b[0m \u001b[0mprop\u001b[0m \u001b[1;32min\u001b[0m \u001b[0mprops\u001b[0m\u001b[1;33m:\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[1;32m----> 2\u001b[1;33m     \u001b[1;32mif\u001b[0m \u001b[0mobj\u001b[0m\u001b[1;33m.\u001b[0m\u001b[0msupports\u001b[0m\u001b[1;33m(\u001b[0m\u001b[0mprop\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m:\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0m\u001b[0;32m      3\u001b[0m         \u001b[1;32mif\u001b[0m \u001b[1;32mnot\u001b[0m \u001b[0mcallable\u001b[0m\u001b[1;33m(\u001b[0m\u001b[0mgetattr\u001b[0m\u001b[1;33m(\u001b[0m\u001b[0mobj\u001b[0m\u001b[1;33m,\u001b[0m\u001b[0mprop\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m:\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0;32m      4\u001b[0m             \u001b[1;32mprint\u001b[0m \u001b[0mprop\u001b[0m\u001b[1;33m,\u001b[0m \u001b[0mgetattr\u001b[0m\u001b[1;33m(\u001b[0m\u001b[0mobj\u001b[0m\u001b[1;33m,\u001b[0m\u001b[0mprop\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n",
      "\u001b[1;31mValueError\u001b[0m: Invalid value for layer_property: 'FINDANDREPLACEWORKSPACEPATH' (choices are: ['CREDITS', 'DATASETNAME', 'WORKSPACEPATH', 'DESCRIPTION', 'BRIGHTNESS', 'SHOWLABELS', 'LONGNAME', 'MAXSCALE', 'SYMBOLOGY', 'SYMBOLOGYTYPE', 'SERVICEPROPERTIES', 'VISIBLE', 'DEFINITIONQUERY', 'DATASOURCE', 'TRANSPARENCY', 'TIME', 'MINSCALE', 'LABELCLASSES', 'CONTRAST', 'NAME'])"
     ]
    }
   ],
   "source": [
    "for prop in props:    \n",
    "    if obj.supports(prop):\n",
    "        if not callable(getattr(obj,prop)):            \n",
    "            print prop, getattr(obj,prop)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "But as you see, the problem remains because we cannot check whether `obj.property` is a callable or not without getting a `ValueError` trying to access `obj.property` first.\n",
    "\n",
    "In such a case, one could use a very handy technique of supressing the exceptions using the `try/except` statement. So, if a property is not supported by this layer and if it is a callable, we don't want to keep this property. We will be able to continue running the `for` loop leaving in the `supported_props` list only valid properties."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 12,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Unsupported properties: ['brightness', 'contrast', 'findAndReplaceWorkspacePath', 'getExtent', 'getSelectedExtent', 'getSelectionSet', 'replaceDataSource', 'save', 'saveACopy', 'serviceProperties', 'setSelectionSet', 'supports', 'symbology', 'updateLayerFromJSON']\n",
      "\n",
      "Supported properties: ['credits', 'dataSource', 'datasetName', 'definitionQuery', 'description', 'isBroken', 'isFeatureLayer', 'isGroupLayer', 'isNetworkAnalystLayer', 'isRasterLayer', 'isRasterizingLayer', 'isServiceLayer', 'labelClasses', 'longName', 'maxScale', 'minScale', 'name', 'showLabels', 'symbologyType', 'time', 'transparency', 'visible', 'workspacePath']\n"
     ]
    }
   ],
   "source": [
    "unsupported_props = []\n",
    "supported_props = []\n",
    "\n",
    "#get all props for Layer object\n",
    "for prop in [prop for prop in dir(obj) if '_' not in prop]:\n",
    "    try:        \n",
    "        if callable(getattr(obj,prop)): #exclude methods\n",
    "            unsupported_props.append(prop)\n",
    "            continue\n",
    "        else:\n",
    "            getattr(obj,prop) #check whether obj.supports(prop) raises ValueError\n",
    "            supported_props.append(prop)\n",
    "    except:\n",
    "        unsupported_props.append(prop)\n",
    "        \n",
    "print 'Unsupported properties:', unsupported_props\n",
    "print\n",
    "print 'Supported properties:', supported_props"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Now we can safely iterate through every property of this particular map layer:"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 13,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "credits >>> \n",
      "dataSource >>> C:\\GIS\\Temp\\test.gdb\\GridFeatures\n",
      "datasetName >>> GridFeatures\n",
      "definitionQuery >>> \n",
      "description >>> \n",
      "isBroken >>> False\n",
      "isFeatureLayer >>> True\n",
      "isGroupLayer >>> False\n",
      "isNetworkAnalystLayer >>> False\n",
      "isRasterLayer >>> False\n",
      "isRasterizingLayer >>> False\n",
      "isServiceLayer >>> False\n",
      "labelClasses >>> [<LabelClass object at 0x5af5950[0x51e0ed8]>]\n",
      "longName >>> GridLayer\n",
      "maxScale >>> 0.0\n",
      "minScale >>> 0.0\n",
      "name >>> GridLayer\n",
      "showLabels >>> False\n",
      "symbologyType >>> OTHER\n",
      "time >>> <geoprocessing Layer Time object object at 0x0368E900>\n",
      "transparency >>> 0\n",
      "visible >>> True\n",
      "workspacePath >>> C:\\GIS\\Temp\\test.gdb\n"
     ]
    }
   ],
   "source": [
    "for prop in supported_props:\n",
    "    print prop, \">>>\", getattr(obj,prop)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Another way to list out the values only for valid properties is to use the `hasattr()` method:"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 14,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "dataSource >>> C:\\GIS\\Temp\\test.gdb\\GridFeatures\n",
      "datasetName >>> GridFeatures\n",
      "isFeatureLayer >>> True\n",
      "labelClasses >>> [<LabelClass object at 0x5dbdb70[0x37dbe90]>]\n",
      "longName >>> GridLayer\n",
      "name >>> GridLayer\n",
      "symbologyType >>> OTHER\n",
      "time >>> <geoprocessing Layer Time object object at 0x0541F030>\n",
      "visible >>> True\n",
      "workspacePath >>> C:\\GIS\\Temp\\test.gdb\n"
     ]
    }
   ],
   "source": [
    "for prop in [prop for prop in dir(obj) if '_' not in prop]:\n",
    "    if hasattr(obj,prop):\n",
    "        if not callable(getattr(obj,prop)):\n",
    "            if getattr(obj,prop):\n",
    "                print prop, '>>>', getattr(obj,prop)"
   ]
  } 
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