2.7 KiB
2.7 KiB
title | localeTitle |
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The Python Range | Python范围 |
Python范围
范围实际上是不可变的序列类型 ,而不是函数,通常用于在for循环中循环特定次数。
创建:
ranges
是使用range
构造函数创建的。构造函数的参数是:
start
:包含范围的第一个值(可选整数,默认为0)。stop
:独占停止值,当提供此值或更大值时,范围停止(必需整数)。step
:添加到当前值以获取下一个值的量(可选整数,默认为1)。
>>> range(10) # Only the stop parameter is required.
range(0, 10)
>>> range(0, 10) # Default for start parameter is 0.
range(0, 10)
>>> range(0, 10, 1) # Default for step is 1\. Start parameter is required if
step is needed.
range(0, 10)
例子:
由于ranges
是可迭代的,因此可以将它们传递给list
和tuple
构造函数以创建这些类型的序列。使用这个事实,我们可以想象一些例子:
>>> list(range(10)) # range as argument for list constructor.
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
>>> tuple(range(10)) # range as argument for tuple constructor.
(0, 1, 2, 3, 4, 5, 6, 7, 8, 9)
零长度ranges
:
>>> list(range(10, 0)) # start greater than stop with postive step.
[]
>>> list(range(10, 10)) # start equal to stop with postive step.
[]
>>> list(range(10, 10, -1)) # start equal to stop with negative step.
[]
>>> list(range(0, 10, -1)) # start less than stop with negative step.
[]
带步长参数的ranges
:
>>> list(range(0, 10, 2)) # next value would be 10, stops at 8.
[0, 2, 4, 6, 8]
>>> list(range(0, 10, 3)) # next value would be 12, stops at 9.
[0, 3, 6, 9]
>>> list(range(0, 10, 4)) # next value would be 12, stops at 8.
[0, 4, 8]
>>> list(range(10, 0, -1)) # negative step makes decreasing ranges.
[10, 9, 8, 7, 6, 5, 4, 3, 2, 1]
>>> list(range(-5, -30, -3)) # negative integers are valid arguments.
[-5, -8, -11, -14, -17, -20, -23, -26, -29]
优点:
使用range
的好处是,无论指定的范围有多大,只需要少量内存来存储range
,即start,stop和step的值。在迭代时计算ranges
的各个值。
>>> import sys
>>> a_range = range(1000000)
>>> a_list = list(a_range)
>>> a_tuple = tuple(a_range)
>>> sys.getsizeof(a_range)
48
>>> sys.getsizeof(a_list)
9000112
>>> sys.getsizeof(a_tuple)
8000048
更多信息:
TODO:方法ranges
是否实现