如何在python中循环浏览列表列表

需要在列表列表中循环并测试字符串是否为黑色或红色，然后在列表中的浮点值上加或减-例如，如果黑色，则加1；如果字符串值为红色，则减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)

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你很接近。这应该做到：

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

这应该行得通

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)

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您还可以使用列表：

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

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非常感谢。还有Sam.Pierre在回答中比你略胜一筹。非常感谢J。