updating dictionaries from/to dictionaries

[Edwin.Madari at VerizonWireless.com]

if the values for any of the keys are None, both do not work as can be seen below!!. 

since both loops are iterating over keys(), 'get' method which would return a '0' for non existing key does not encounter any non-existing keys.
============================================================
import copy, sys

foo = { 'one' : 1, 'two' : 2, 'three' : None  }
bar = copy.deepcopy(foo)

try:
   for key in foo:
      foo[key] += bar.get(key, 0)
except:
   print 'foo',  sys.exc_info()[:2]

try:
   for key in bar:
      foo[key] += bar[key]
except:
   print 'bar', sys.exc_info()[:2]
========================================
foo (<type 'exceptions.TypeError'>, TypeError("unsupported operand type(s) for +=: 'NoneType' and 'NoneType'",))
bar (<type 'exceptions.TypeError'>, TypeError("unsupported operand type(s) for +=: 'NoneType' and 'NoneType'",))

hope that helps to clarify both point of views.
thanks Edwin

-----Original Message-----
From: python-list-bounces+edwin.madari=verizonwireless.com at python.org
[mailto:python-list-bounces+edwin.madari=verizonwireless.com at python.org]
On Behalf Of Brandon
Sent: Thursday, August 14, 2008 8:35 PM
To: python-list at python.org
Subject: Re: updating dictionaries from/to dictionaries



> (1) iterating over foo:
> for key in foo:
>    foo[key] += bar.get(key, 0)
>
> (2) iterating over bar:
> for key in bar:
>    foo[key] += bar[key]
>
> I (again) challenge you to say *why* you feel that the "iterating over
> bar" solution will not work.


Well if you're going to be clever enough to iterate over bar and then
send the results to another dictionary altogether, I obviously cannot
put up a good argument on this matter!

Thanks for the input, I appreciate it.
--
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