range函数作用

• Python 中的range是表示整数区间的对象，通常用for循环访问。
• range函数t转的对象可以转换为列表
• for i in range(5)是一个循环，它遍历从 0 到 4（包括 0 和 4）的数字。
• range函数参数 、start, stop, step左闭右开[start,end),step数字表示步长
• 在 Python 中，range可以使用负步长值向后移动，也可以使用 .reversed()

使用range函数

>>> list(range(5))
[0, 1, 2, 3, 4]
>>> list(range(1, 7))
[1, 2, 3, 4, 5, 6]
>>> list(range(1, 20, 2))
[1, 3, 5, 7, 9, 11, 13, 15, 17, 19]

生成0, 1, 2, 3, 4这5个数字

range函数返回的对象

>>> range(5)
range(0, 5)

>>> list(range(1, 7))
[1, 2, 3, 4, 5, 6]

range(start,end,step)

>>> range(1, 20, 2)
range(1, 20, 2)

>>> list(range(1, 20, 2))
[1, 3, 5, 7, 9, 11, 13, 15, 17, 19]

• range(1, 20, 2)其中2表示每次数字增2

使用负数生成range

>>> range(-10, 0)
range(-10, 0)
>>> list(range(-10, 0))
[-10, -9, -8, -7, -6, -5, -4, -3, -2, -1]

>>> range(-7, -3)
range(-7, -3)
>>> list(range(-7, -3))
[-7, -6, -5, -4]

使用空范围

>>> range(1, 1)
range(1, 1)
>>> list(range(1, 1))
[]

>>> range(0)
range(0, 0)
>>> list(range(0))
[]

使用负数的步长 range(5, -1, -1)

>>> range(5, -1, -1)
range(5, -1, -1)
>>> list(range(5, -1, -1))
[5, 4, 3, 2, 1, 0]

for循环的使用

遍历字符串

>>> word = "Loop"
>>> for index in range(len(word)):
...     print(index, word[index])
...
0 L
1 o
2 o
3 p

>>> for _ in range(3):
...     print("Knock, knock, knock")
...     print("Penny!")
...
Knock, knock, knock
Penny!
Knock, knock, knock
Penny!
Knock, knock, knock
Penny!

直接在迭代器上循环

>>> word = "Loop"
>>> for index in range(len(word)):
...     print(word[index])

获取索引

>>> word = "Loop"
>>> for index, char in enumerate(word):
...     print(index, char)
...
0 L
1 o
2 o
3 p

更复杂的使用

有一个表示藏宝图的网格。宝藏以 标记。地图的中心位于坐标 （0， 0） 处，并由 .您可以按如下方式查找宝藏的坐标： oenumerate()

>>> grid = """
... .............
... .........X...
... ...X..o......
... .............
... ...........X.
... """.strip()
...
... rows = grid.split("\n")
... for row, line in enumerate(rows, start=-(len(rows) // 2)):
...     for col, char in enumerate(line, start=-(len(line) // 2)):
...         if char == "X":
...             print(f"Treasure found at ({row}, {col})")
...
Treasure found at (-1, 3)
Treasure found at (0, -3)
Treasure found at (2, 5)

多列表访问

>>> grid = """
... .............
... .........X...
... ...X..o......
... .............
... ...........X.
... """.strip()
...
... rows = grid.split("\n")
... for row, line in enumerate(rows, start=-(len(rows) // 2)):
...     for col, char in enumerate(line, start=-(len(line) // 2)):
...         if char == "X":
...             print(f"Treasure found at ({row}, {col})")
...
Treasure found at (-1, 3)
Treasure found at (0, -3)
Treasure found at (2, 5)

也可以使用zip函数简化上述逻辑

>>> countries = ["Norway", "Canada", "Burkina Faso"]
>>> capitals = ["Oslo", "Ottawa", "Ouagadougou"]
>>> for country, capital in zip(countries, capitals):
...     print(f"The capital of {country} is {capital}")
...
The capital of Norway is Oslo
The capital of Canada is Ottawa
The capital of Burkina Faso is Ouagadougou

range的其他用法

>>> numbers = range(1, 20, 2)
>>> list(numbers)
[1, 3, 5, 7, 9, 11, 13, 15, 17, 19]
>>> 
>>> numbers[3]  #获取 第4个数字
7

>>> numbers[-2] #获取 倒数第二个数字

17

>>> list(numbers[1:5]) #取第二个到第第六个数字，不包括第六个
[3, 5, 7, 9]

判断元素是否在range中

>>> year = 2023
>>> year in range(2000, 2100, 4)
False

>>> year = 2024
>>> year in range(2000, 2100, 4)
True 

反转列表

>>> def reverse_range(rng):
...     return range(
...         rng.stop - rng.step,
...         rng.start - rng.step,
...         -rng.step,
...     )
...
>>> reverse_range(range(5, 0, -1))
range(1, 6)

>>> reverse_range(reverse_range(range(5, 0, -1)))
range(5, 0, -1)