列表/数组表示形式[]和{}有什么区别？

Question

What is the difference between :

dictionary = []

and

dictionary = {}

assuming dictionary has string contents ?

Answer 1

In the first case, you're making a list whereas the other you're making a dict . list objects are sequences whereas dict objects are mappings . Have a look at the python types page.

Basically, lists "map" sequential integers (starting at 0) to some object. In that way, they behave a lot more like a dynamic array in other languages. In fact, Cpython implements them as overallocated arrays in C.

dict map hashable keys to an object. They're implemented using hash tables.

---

Also note that starting from python2.7, you can use the {} to create sets as well which are another (fundamental) type. Review:

[] #empty list
{} #empty dict
set() #empty set

[1] #list with one element
{'foo':1} #dict with 1 element
{1} #set with 1 element

[1, 2] #list with 2 elements
{'foo':1, 'bar':2} #dict with 2 elements
{1, 2} #set with 2 elements. 

Answer 2

On python 2.x

>>> type([])
<type 'list'>
>>> type({})
<type 'dict'>
>>>

On python 3.x

>>> type([])
<class 'list'>
>>> type({})
<class 'dict'>
>>>