Python range() 方法

Python中有许多可迭代对象，例如列表、元组等。 range()提供了另一种使用某些条件初始化数字序列的方法。
range()通常用于 for 循环，因此，在处理任何类型的Python代码时，相同的知识是关键方面。

Syntax : range(start, stop, step)
Parameters : 
start : Element from which sequence constructed has to start. (default:0) 
stop : Element number at which numbers in sequence have to end (exclusive). 
step : Can be +ve or -ve number, denoting the elements need to be skipped during filling of list. (default:1)
Returns : The list using the formula : 
list[n] = start + step*n (for both positive and negative step) where, n >=0 and list[n] = 0 and list[n] > stop (for negative step)
Returns ValueError if step is 0. Value constraint is checked in case of step, failing to meet returns empty sequence, else returns sequence according to formula. 
 

代码 #1：演示 range() 没有 step 参数

Python3

# Python3 code to demonstrate the
# working of range() without step
 
# using range()
lis1 = list(range(6))
lis2 = list(range(3, 6))
lis3 = list(range(-6, 2))
 
# initializing list using range, 1 parameter
# only stop parameter
print("List generated using 1 parameter : " + str(lis1))
 
# initializing list using range, 2 parameters
# only step and stop parameters
print("List generated using 2 parameters : " + str(lis2))
 
# initializing list using range, 2 parameter
# only step and stop parameters
print("List generated using 2 parameters with negatives : " + str(lis3))

输出：

List generated using 1 parameter : [0, 1, 2, 3, 4, 5]
List generated using 2 parameters : [3, 4, 5]
List generated using 2 parameters with negatives : [-6, -5, -4, -3, -2, -1, 0, 1]

代码 #2：使用 step 演示 range()

Python3

# Python 3 code to demonstrate the
# working of range() with step
 
# initializing list using range
# using step
print("List generated using step : " +
    str(list(range(3, 10, 2))))
 
# initializing list using range
# using negative step
print("List generated using negative step : " +
                  str(list(range(10, -5, -3))))
 
# initializing list using range
# using negative step,
# value constraints fail case
print("List generated using step, value constraints fail : " +
                                 str(list(range(10, -5, 3))))
 
# initializing list using range
# using 0 step
# error
print("List generated using 0 step : " +
              str(list(range(3, 7, 0))))

输出：

List generated using step : [3, 5, 7, 9]
List generated using negative step : [10, 7, 4, 1, -2]
List generated using step, value constraints fail : []

例外：

Traceback (most recent call last):
  File "/home/bdae725dff7b38d3681eee38f6a6d434.py", line 23, in 
    print("List generated using 0 step : " + str(list(range(3, 7, 0))))
ValueError: range() arg 3 must not be zero