sorting - Porting sort with lambda function to Python 3 -

i'm porting code python 2.7 3. 2to3 not convert following lines , can't seem figure out. appreciated.

subpaths.sort(     lambda x, y :         int(pyx.unit.tocm(x.arclen() - y.arclen()) /             math.fabs(pyx.unit.tocm(x.arclen() - y.arclen()))) ) 

the sort method of list requires key, function of 1 argument. need convert lambda function function of single argument. there shortcut provided functools.cmp_to_key. thus, need is:

import functools subpaths.sort(key=functools.cmp_to_key(lambda x, y: ...)) 

note if understand code correctly, can sort list using following key:

subpaths.sort(key=lambda x: pyx.unit.tocm(x.arclen()))