Python 元组

元组

• 创建一系列不可修改的元素，Python中不能修改的值称为不可变的，不可变的列表称为元祖。

定义元组

• 使用圆括号而不是方括号来标识，定义元组后可以用索引来访问其元素

# 定义元祖案例
# 长方形的长和宽放入元组中不能进行修改
dimensions = (200,50)
print(dimensions[0])
print(dimensions[1])
# 元组中的值不能进行修改
dimensions[0] = 250

200
50



---------------------------------------------------------------------------

TypeError                                 Traceback (most recent call last)

<ipython-input-2-2db727e7a6e4> in <module>()
      4 print(dimensions[0])
      5 print(dimensions[1])
----> 6 dimensions[0] = 250


TypeError: 'tuple' object does not support item assignment

遍历元组中的所有值

• 使用for循环遍历元组中的所有值

dimensions = (200,50)
for dimension in dimensions:
    print(dimension)

200
50

修改元组变量

• 虽然不能修改元组的值，但可以给存储元组的变量赋值（重新定义整个元组）

dimensions = (200,50)
print("Original dimensions:")
for dimension in dimensions:
    print(dimension)

dimensions = (400,100)
print("\nModified dimensions:")
for dimension in dimensions:
    print(dimension)

Original dimensions:
200
50

Modified dimensions:
400
100

练习

# 1.自助餐
# 餐厅提供五种简单的食品，写出五种食品并存储到一个元组中
# 使用一个for循环将食品打印出来
# 修改其中一个元素。让Python提示拒绝这样做
# 替换其中2中食品，给元组变量赋值，并使用一个for循环将新的元组中的每个元素打印
restaurant = ("西红柿","黄瓜","水蜜桃","腊肉","红烧肉")
for food in restaurant:
    print(food)
restaurant[1] = "茄子"

西红柿
黄瓜
水蜜桃
腊肉
红烧肉



---------------------------------------------------------------------------

TypeError                                 Traceback (most recent call last)

<ipython-input-8-9cdf694f1019> in <module>()
      7 for food in restaurant:
      8     print(food)
----> 9 restaurant[1] = "茄子"
     10 restaurant = ("西红柿","黄瓜","水蜜桃","香蕉","番茄")
     11 for foods in restaurant:


TypeError: 'tuple' object does not support item assignment

restaurant = ("西红柿","黄瓜","水蜜桃","香蕉","番茄")
for foods in restaurant:
    print(foods)

西红柿
黄瓜
水蜜桃
香蕉
番茄