What is a typical way to add a reverse feature to an insertion sort?

Question

I wrote the following insertion sort algorithm

def insertionSort(L, reverse=False):
    for j in xrange(1,len(L)):
        valToInsert = L[j]
        i=j-1
        while i>=0 and L[i] > valToInsert:
            L[i+1] = L[i]
            i-=1
        L[i+1] = valToInsert
    return L

Edit: All you need to do is change the final > to < to get it to work in reverse.

However, what do most people do in these situations? Write the algorithm twice in two if-statements, one where it's > and the other where it's < instead? What is the "correct" way to typically handle these kinds of scenarios where the change is minor but it simply changes the nature of the loop/code entirely?

I know this question is a little subjective.

Answer 1

You could use a variable for the less-than operator:

import operator
def insertionSort(L, reverse=False):       
    lt = operator.gt if reverse else operator.lt        
    for j in xrange(1,len(L)):
        valToInsert = L[j]
        i = j-1
        while 0 <= i and lt(valToInsert, L[i]):
            L[i+1] = L[i]
            i -= 1
        L[i+1] = valToInsert
    return L

Answer 2

Option 1:

def insertionSort(L, reverse=False):
    # loop is the same...
    if reverse:
        L.reverse()
    return L

Option 2:

def insertionSort(L, reverse=False):
    if reverse:
        cmpfunc = lambda a, b: cmp(b, a)
    else:
        cmpfunc = cmp
    for j in xrange(1,len(L)):
        valToInsert = L[j]
        i=j-1
        while i>=0 and cmpfunc(L[i], valToInsert) > 0:
            L[i+1] = L[i]
            i-=1
        L[i+1] = valToInsert
    return L