Python中的sum（）函数-yiteyi-C++库

列表中的数字总和在任何地方都是必需的。Python提供了一个内置函数sum（），用于汇总列表中的数字。 语法：

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sum(iterable, start)  
iterable : iterable can be anything list , tuples or dictionaries ,
 but most importantly it should be numbers.
start : this start is added to the sum of 
numbers in the iterable. 
If start is not given in the syntax , it is assumed to be 0.

可能有两种语法：

sum(a)
a is the list , it adds up all the numbers in the 
list a and takes start to be 0, so returning 
only the sum of the numbers in the list.
sum(a, start)
this returns the sum of the list + start

下面是sum（）的Python实现

                     # Python code to demonstrate the working of                   
                     # sum()                   
                             
                     numbers                               =                               [                               1                               ,                               2                               ,                               3                               ,                               4                               ,                               5                               ,                               1                               ,                               4                               ,                               5                               ]                   
                             
                     # start parameter is not provided                   
                     Sum                               =                               sum                               (numbers)                   
                     print                               (                               Sum                               )                   
                             
                     # start = 10                   
                     Sum                               =                               sum                               (numbers,                               10                               )                   
                     print                               (                               Sum                               )                   

输出：

25
35

错误和例外

类型错误： 如果列表中有其他数字，则会出现此错误。

                     # Python code to demonstrate the exception of                   
                     # sum()                   
                     arr                               =                               [                               "a"                               ]                   
                             
                     # start parameter is not provided                   
                     Sum                               =                               sum                               (arr)                   
                     print                               (                               Sum                               )                   
                             
                     # start = 10                   
                     Sum                               =                               sum                               (arr,                               10                               )                   
                     print                               (                               Sum                               )                   

运行时错误：

Traceback (most recent call last):
  File "/home/23f0f6c9e022aa96d6c560a7eb4cf387.py", line 6, in 
    Sum = sum(arr)
TypeError: unsupported operand type(s) for +: 'int' and 'str'

所以列表应该包含数字

实际应用： 需要求和才能进行进一步运算的问题，例如求出数字的平均值。

                     # Python code to demonstrate the practical application                   
                     # of sum()                   
                             
                     numbers                               =                               [                               1                               ,                               2                               ,                               3                               ,                               4                               ,                               5                               ,                               1                               ,                               4                               ,                               5                               ]                   
                             
                     # start = 10                   
                     Sum                               =                               sum                               (numbers)                   
                     average                               =                               Sum                               /                               len                               (numbers)                   
                     print                               (average)                   

输出：

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