Getting ready

The arcpy.mapping module contains various list functions to return lists of layers, data frames, broken data sources, table views, and layout elements. These list functions are normally the first step in a multi-step process, where the script needs to get one or more items from a list for further processing. Each of these list functions returns a Python list, which as you know from earlier in the book, is a highly functional data structure for storing information.

Normally, the list functions are used as part of a multi-step process, where creating a list is only the first step. Subsequent processing in the script will iterate over one or more of the items in this list. For example, you might obtain a list of layers in a map document and then iterate through each layer looking for a specific layer name, which will then be subject to further geoprocessing.

In this recipe, you will learn how to obtain a list of layers from a map document file.

How to do it…

Follow these steps to learn how to get a list of layers from a map document:

How it works…

The ListLayers() function retrieves a list of layers in a map document, a specific data frame, or a layer file. In this case, we passed a reference to the current map document to the ListLayers() function, which will retrieve a list of all layers in the map document. The results will be stored in a variable called layers, which is a Python list that can be iterated with a for loop. This Python list contains one or more Layer objects.

There's more…

The ListLayers() function is only one of many list functions provided by the arcpy mapping module. Each of these functions returns a Python list containing data of some type. Some of the other list functions include ListTableViews(), which returns a list of Table objects, ListDataFrames() which returns a list of DataFrame objects, and ListBookmarks() which returns a list of bookmarks in a map document. There are additional list functions, many of which we'll cover later in the book.