python3-列表字典简单练习题

.求全部元素的和[,,,,,,,]
>>> a=[,,,,,,,]
>>> result=
>>> for i in a:
...     result+=i
...
>>> print (result)

.求偶数元素的和[,,,,,,,]
方法一：只适用于当前list
>>> a=[, , , , , , , ]
>>> res=
>>> for i in a[::]:
...     res+=i
...
>>> print (res)

方法二：适用于任何list
>>> a=[, , , , , , , ]
>>> res=
>>> for i in a:
...     if i%==:
...        res+=i
...
>>> print(res)

.统计一下所有数字出现的个数[,,,,,,,]
>>> d={}
>>> for i in a:
...     d[i]=""
...
>>> d
{: '', : '', : ''}
>>> d.keys()
dict_keys([, , ])
>>> list(d.keys())
[, , ]
>>> for i in list(d.keys()):
...     print("数字"+str(i)+"共出现了:"+str(a.count(i))+"次")
...
数字1共出现了:2次
数字2共出现了:2次
数字3共出现了:4次