在迭代器中求和

Question

下面的代码显示所需的输出-10

Details
abort: 'https://xxxxx.visualstudio.com/xxxxx/_git/XXXXX' does not appear to be an hg repository:

svn: E170013: Unable to connect to a repository at URL 'https://xxxxx.visualstudio.com/xxxxx/_git/xxxxxx'
svn: E230001: Server SSL certificate verification failed: issuer is not trusted

如果我在这两行之间再添加一行代码，则输出更改为0

values = iter(range(1, 5))
sum(values)

Answer 1

Python iterators是可耗尽的对象，这意味着它们在您调用它们时就被用尽。

• 1 ^rst 示例：

  values = iter(range(1, 5))  # <- iterator is created
  sum(values)                 # <- all of it is used at once
  

• 2 ^nd 示例：

  values = iter(range(1, 5))  # <- iterator is created
  values_list = list(values)  # <- all of it is used at once
  sum(values)                 # <- nothing left to sum :(
  

如果您想一遍又一遍地使用某些内容，iterator数据类型不适合您；改用list。