operator.itemgetter() syntax

[rogerlew]

Hi all,

I need to pass operator.itemgetter(item,...) multiple arguments but the number of arguments is variable.

ivlist=['var1','var2','var3'] # This variable changes length
keyindices=range(-len(ivlist)-1,0) # = [-4, -3, -2, -1] in this example
 
# What I want in this example is
M_keys=M.keys()
for key in sorted(M_keys,key=operator.itemgetter(-4, -3, -2, -1)):
    # for loop code
 

What is the syntax for passing operator.itemgetter(items,...) the values of the keyindices list as separate arguments?

Thank you for your help.

[rogerlew]

I figured it out.

for key in sorted(M_keys,key=operator.itemgetter(*keyindices)):
 

[ilikepython]

I figured it out.

for key in sorted(M_keys,key=operator.itemgetter(*keyindices)):
 

Glad you fixed your problem. :)

[rogerlew]

The method described above works for Python 2.5 but not for 2.4.4. Operator.itemgetter only accepts one argument under 2.4.4. Another problem I found was that with 2.5 the * will only flatten a sequence. So if you want to sort by unordered a set of unordered indices (e.g. -1, 4,5,6) your out of luck (from want I tried at least).

I ended writing a function which works with 2.4 and 2.5. I am posting it here encase someone runs into the same problem and happens to google this in the future.

def SortKeyByIndices(keylist,indices):
    sortedkeys=sorted(keylist,key=operator.itemgetter(indices[0]))
    if len(indices)>1:
        teeth=[]
        teeth.append([sortedkeys[0][indices[0]],0])
        for ikey, key in enumerate(sortedkeys):
            if key[indices[0]]!=teeth[-1][0]:
                teeth.append([key[indices[0]],ikey])
        teeth.append([teeth[-1][0],len(sortedkeys)])
        for tnum, tooth in enumerate(teeth[:-1]):
            subkeys=sortedkeys[teeth[tnum][1]:teeth[tnum+1][1]]
            subkeys=SortKeyByIndices(subkeys,indices[1:])
            sortedkeys[teeth[tnum][1]:teeth[tnum+1][1]]=subkeys
    return sortedkeys
 

Usage

mykeys=mylist.keys()
mykeyssorted=SortKeyByIndices(mykeys,[1,2,5,6])