如何在python中遍历列表列表

Question

需要遍历列表列表并测试字符串是黑色还是红色，然后从列表的浮点数中添加或减去-例如，如果“ Black”添加1，或者如果字符串值为“ Red”则减去1

new_line = [["Black", 3.0], ["Red", 7.0], ["Red", 2.0], ["Black", 3.5]]

for i in new line:
    if value == "Black":
          add =+ 1 to float value (3.0 in first example)
    else: 
          subtract -=1 float value (7.0 in second value n list)

Answer 1

你很亲密 应该这样做：

new_line = [["Black", 3.0], ["Red", 7.0], ["Red", 2.0], ["Black", 3.5]]

for i in new_line:
    if i[0] == "Black":
          i[1] += 1
    else: 
          i[1] -=1

Answer 2

这应该工作

new_line = [["Black", 3.0], ["Red", 7.0], ["Red", 2.0], ["Black", 3.5]]

for i in new_line:
     if i[0] == "Black":
          i[1] += 1.0
     else: 
          i[1] -= 1.0

 print(new_line)

Answer 3

您还可以使用列表理解：

new_line = [[color,value+(color=="Black")*2-1] for color,value in new_line]