Schwartzian Transform in python

 The technique, attributed to Randal Schwartz of the Perl community, sorts the elements of a list by a metric which maps each element to its "sort value". In Python, just use the key argument for the sort() method: Isorted = L[:] Isorted.sort(key=lambda s: int(s[10:15])) The key argument is new in Python 2.4, for older versions this kind of sorting is quite simple to do with list comprehensions. To sort a list of strings by their uppercase values: tmp1 = [(x.upper(), x) for x in L]  # Schwartzian transform tmp1.sort() Usorted = [x[1] for x in tmp1] To sort by the integer value of a subfield extending from positions 10-15 in each string: tmp2 = [(int(s[10:15]), s) for s in L]  # Schwartzian transform tmp2.sort() Isorted = [x[1] for x in tmp2] For versions prior to 3.0, Isorted may also be computed by def intfield(s):     return int(s[10:15]) def Icmp(s1, s2):     return cmp(intfield(s1), intfield(s2)) Isorted = L[:] Isorted.sort(Icmp) but since this method calls intfield() many times for each element of L, it is slower than the Schwartzian Transform.