replace dict contents

[Robin Becker]

Peter Otten wrote:
> Tim Jarman wrote:
> 
> 
>>On 27 Jul 2004, at 08:56, Robin Becker wrote:
>>
>>
>>>Is there a simple way to replace the contents of a dictionary entirely
>>>with those of another.
>>>
>>>for lists we can do
>>>
>>>L1[:] = L2
> 
> 
> 
>>How about:
>>
>> >>> d1 = { "spam" : "eggs" }
>> >>> d2 = { "gumby" : "my brain hurts!"}
>> >>> d1 is d2
>>False
>> >>> d1 = dict(d2)
> 
> 
> This rebinds the name d1 to a copy of d2 and will not affect other
> references to the original d1.
> 
> Peter
Peter has the essence of the problem. Attempts to change sys.modules 
have strange effects eg try this simple script

import sys
omods = sys.modules
sys.modules = omods.copy()

print 'start', len(sys.modules), len(omods)
import urlparse
print 'after import', len(sys.modules), len(omods)


In my executions it's len(omods) that changes
so we need a way to copy the original sys.modules and then quickly 
replace uf we want to restore the original value.

The actual replace part of  L1[:]=L2 happens in a single opcode and is 
therefore atomic. The same cannot be said of the .clear, .update sequence.
-- 
Robin Becker