Python dictionary iteration

Question

I have a dictionary dict2 which I want to iter through and remove all entries that contain certain ID numbers in idlist. dict2[x] is a list of lists (see example dict2 below). This is the code I have written so far, however it does not remove all instances of the IDs (entry[1]) that are in the idlist. Any help?

dict2 = {G1:[[A, '123456', C, D], [A, '654321', C, D], [A, '456123', C, D], [A, '321654', C, D]]}
idlist = ['123456','456123','321654']
for x in dict2.keys():
 for entry in dict2[x]:
 if entry[1] in idlist:
 dict2[x].remove(entry)
 if dict2[x] == []:
 del dict2[x]

dict2 should end up looking like this :

dict2 = {G1:[[A, '654321', C, D]]}

Answer 1

Try a cleaner version perhaps?

for k in dict2.keys():
 dict2[k] = [x for x in dict2[k] if x[1] not in idlist]
 if not dict2[k]:
 del dict2[k]

• Ben Hoyt: Note that you can't modify a dict while iterating over it, so @marsx was right to iterate over dict2.keys() instead.
• Amber: @benhoyt - you're right; I initially took it out because I forgot about the del, but then put the del in and didn't swap it back. :)
• marsx: @Amber I didnt type it right but the ID numbers are all strings. I tried your code and I got this error dict2[x] = [x for x in dict2[k] if x[1] not in idlist] TypeError: list objects are unhashable. I dont know if this makes a difference but the real dict2 contains datetime objects and other lists aswell.
• Amber: If you're getting that error, your dict2 has an additional layer of nesting beyond what you wrote here, or the wrong index in the list is being used.
• marsx: @Amber should it be dict2[k] = [x for x in dict2[k] if x[1] not in idlist] ? dict2[x] doesnt make sense if you're calling the lists x

Answer 2

An approach using sets (Note that I needed to change your variables A, B, C, etc. to strings and the numbers in your idlist to actual integers; also this only works, if your IDs are unique and don't occur in other 'fields'):

#!/usr/bin/env python
# 2.6 <= python version < 3
original = {
 'G1' : [
 ['A', 123456, 'C', 'D'], 
 ['A', 654321, 'C', 'D'], 
 ['A', 456123, 'C', 'D'], 
 ['A', 321654, 'C', 'D'],
 ]
}
idlist = [123456, 456123, 321654]
idset = set(idlist)
filtered = dict()
for key, value in original.items():
 for quad in value:
 # decide membership on whether intersection is empty or not
 if not set(quad) & idset:
 try:
 filtered[key].append(quad)
 except KeyError:
 filtered[key] = quad
print filtered
# would print:
# {'G1': ['A', 654321, 'C', 'D']}