[GIS] Create Python Dictionary from feature classes, fields, and domains

arcpydictionaryfeature-class

I want to create a Python dictionary with a Feature class as the key and the fields of the feature class and domains of the feature class as separate values. I'm starting off by simply attempting to add a Feature class (as a key) and its respective feature types(as values) but I'm not sure how to build that out. here's what I am trying to do by using list comprehension but my dictionary is empty:

    Dict = {fc.name: fc.featureType.values()for fc in arcpy.ListFeatureClasses(r"gdb")}

    print Dict

Any clues on how I can start this off?

Best Answer

As an alternative to list comprehension, and to try and learn more about using dictionaries with ArcPy I think you should start with an empty dictionary and then use Describe to determine and add the values as you iterate ListFeatureClasses.

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You're better off using the Calculate Field tool in ArcGIS to achieve the results you are looking for since you can better specify linkages between each row in your table and the resulting value of "Calculated Footage".

The method (list/looping) you are using above is not the best programming practice for this job. Some information on field calculation fundamentals are available here. Likewise, here are some examples. Your best bet, if possible, will be to break down the calculation into a format which can be carried out across each row, for example: column4 + column 6 = "Calculated Footage".

Where possible, lists/looping should be avoided when populating tables as there is a lot of room for errors to creep in (e.g. missing/deleted FIDs). The Calculate Field tool, which can be scripted using Python is more reliable.

[GIS] Creating a dict with Search Cursor

collections.defaultdict works brilliantly here.

Consider the following:

from collections import defaultdict
intDict, listDict = defaultdict(int), defaultdict(list)    

for i in xrange(15):
    if i % 4:
        intDict["A"] += 1
        listDict["A"].append(i)
    else:
        intDict["B"] += 1
        listDict["B"].append(i)

>>>print(intDict)
defaultdict(<type 'int'>, {'A': 11, 'B': 4})
>>>print(listDict)
defaultdict(<type 'list'>, {'A': [1, 2, 3, 5, 6, 7, 9, 10, 11, 13, 14], 'B': [0, 4, 8, 12]})

Remember that dictionary keys must be hashable (so one of the immutable data types). Depending on your needs, you might want a tuple as a key, or even some nested dictionaries.

Best Answer

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