building a dictionary dynamically

Richard Thomas chardster at
Sun Feb 5 03:18:30 CET 2012

On Feb 4, 6:13 pm, noydb <jenn.du... at> wrote:
> How do you build a dictionary dynamically?  Doesn't seem to be an
> insert object or anything.  So I need an empty dictionary that I then
> want to populate with values I get from looping through a list and
> grabbing some properties.  So simply, I have (fyi, arcpy = module for
> interacting with gis data)
> >>> inDict = {}
> >>> for inFC in inFClist:
> >>>     print inFC
> >>>     inCount =  int(arcpy.GetCount_management(inFC).getOutput(0))
> where I want to make a dictionary like {inFC: inCount, inFC:
> inCount, ....}
> How do I build this???
> And, is dictionaries the best route go about doing a comparison, such
> that in the end I will have two dictionaries, one for IN and one for
> OUT, as in I'm moving data files and want to verify that the count in
> each file matches between IN and OUT.
> Thanks for any help!

Dictionaries are mutable, you can modify them in place:

>>> myDict = {}
>>> for myKey in myList:
...     myDict[myKey] = doSomething(myKey)

Dictionaries sound like a good way to go. You only need the one
dictionary though, the IN one. When processing the outCount values you
can just check them against the inDict at that point.


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