[Pythonic] 迴圈計數應用 enumerate()

在Python中，for迴圈可用來遍訪字串、串列等iterator，若要計算迴圈的數量，可在迴圈
中用counter來記錄。

seq = ["one", "two", "three", "four", "five"]
counter = 0
for e in seq:
  print (counter, e)
  counter += 1

1 one
2 two
3 three
4 four
5 five

另外還有比較Pythonic的寫法，就是使用enumerate (sequence, [start=0]) 函數。
sequence代入iterator，start則為起始位置。

seq = ["one", "two", "three", "four", "five"]
for idx, e in enumerate(seq):
  print (idx, e)

1 one
2 two
3 three
4 four
5 five