Selection Sort in Python

Question

This may seem like a simple question but when I attempted to implement selection sort in Python, I do not get a sorted list. Is there something wrong with my implementation? The subsetting may be a problem.

source = [4,2,1,10,5,3,100]
for i in range(len(source)):
  mini = min(source[i:]) #find minimum element
  min_index = source[i:].index(mini)-1 #find index of minimum element
  source[i:][min_index]= source[i:][0] #replace element at min_index with first element
  source[i:][0] = mini                  #replace first element with min element
print source