Python for loop start counter initialization

问题

for iteration in range(len(list) - 1):
  index = iteration +1 #This is the line which has no effect on the inner loop
  for index in range(len(list)):
    if list[iteration] > list[index]:
      newmin  = list[index]
      newminindex = index        
  if iteration != newminindex :
    swapnumbers(list,iteration, newminindex)

The above is a code snippet I wrote for selection sort algorithm. However I see the inner loop start counter always starting from 0. Request for expert comment.

回答1:

The for index in range(len(list)) loop executes the loop body with index first set to 0, then 1, then 2, etc. up to len(list) - 1. The previous value of index is ignored and overwritten. If you want index to start at iteration + 1, use the 2-argument form of range:

for index in range(iteration + 1, len(list)):

回答2:

You really should be using enumerate for stuff like this, as you can loop through the index and the value at the same time (which will save you the hassle of using two for-loops).

for i, j in enumerate(list):
    print i, j

Your inner loop is overriding the variable index that you defined in the first loop.

回答3:

for index in range(iteration + 1, len(list))

回答4:

Try this instead:

for index in range(iteration + 1, len(l)):  # don't use "list" as a name

index is being reassigned anyway within the for-loop so index = iteration + 1 is not having any effect.

来源：https://stackoverflow.com/questions/17498407/python-for-loop-start-counter-initialization

标签

python

loops

for-loop