列表推导

#列表推导做用时生成列表，可读性好，但是如果超过两行的就要使用for
colors = ["black","white"]
sizes = ["S","M","L"]
tshirts = [(color,size) for color in colors for size in sizes ]
print(tshirts)

tshirts = [(color,size) for color in colors for size in sizes if size == "M"]
print(tshirts)