string.sort(), sorted(), reverse, set(), list slice,list comprehension

一些小结 : 

The sort()method changes the ordering of lists in-place.

直接修改list顺序的方法.

>>> l=[1,2,3,2,3,4,1]
>>> l.sort()
>>> print(l)
[1, 1, 2, 2, 3, 3, 4]

The sorted() BIF sorts most any data structure by providing copied sorting.

修改list顺序的内建函数, 但是不修改list变量本身, 只是输出另一个list

>>> l=[1,2,3,2,3,4,1]
>>> sorted(l)
[1, 1, 2, 2, 3, 3, 4]
>>> print(l)
[1, 2, 3, 2, 3, 4, 1]

Pass reverse=True to either sort()or sorted()to arrange your data in descending order.

sort()和sorted()的反向排序参数reverse=True

>>> sorted(l,reverse=True)
[4, 3, 3, 2, 2, 1, 1]

When you have code like this: 

  new_l = []
  for t in old_l:
    new_l.append(len(t))

rewrite it to use a list comprehension, 

like this: 

new_l = [len(t) for t in old_l]

list轮询处理产生另一个list的缩写

>>> l=[1,2,3,2,3,4,1]
>>> print([x*2 for x in l])
[2, 4, 6, 4, 6, 8, 2]

To access more than one data item from a list, use a slice. For example: 

my_list[3:6] 

accesses the items from index location 3 up-to-but-not-including index location 6.

list slice的访问方法, 不包含最大值索引.(索引从0开始), 反向索引从-1开始.

>>> l=[0,1,2,3,4,5,6,7]
>>> print(l[-3:-1])
[5, 6]
>>> print(l[0:3])
[0, 1, 2]

Createa setusing the set() factory function.

不带重复, 无序的list新类型set.

在没有set时, list可以使用以下方法去重复.

>>> l=[1,3,1,3,1,3]
>>> for i in l:
...   if i not in new_l:
...     new_l.append(i)
...
>>> print(new_l)
[1, 3]

使用set()去重

>>> new_set=set(l)
>>> print(new_set)
{1, 3}

创建set类型的方法:

>>> new_set1=set()
>>> print(type(new_set1))
<class 'set'>

以下方法创建的是dict类型

>>> new_set2={}
>>> print(type(new_set2))
<class 'dict'>