What Python is Dict

We already know that list and tuple can be used to represent sequential collections, for example, the name of the class:

[' Adam ', ' Lisa ', ' Bart ']

Or the test results list:

[95, 85, 59]

However, to find the corresponding score according to the name, it is inconvenient to use two list to indicate.

If you associate a name with a score, make a similar look-up table:

' Adam ' ==> ' Lisa ' ==> ' Bart ' ==> 59

Given a name, you can find the score directly.

Python's dict is dedicated to doing this. The lookup table for "name"-"score" is shown in dict as follows:

D = {    ' Adam ': +,    ' Lisa ': $,    ' Bart ': 59}

We call the name key, the corresponding result is called value, Dict is the key to find value.

The curly braces {} indicate that this is a dict, and then follow the key:valueand write them out. The last comma of a key:value can be omitted.

Since Dict is also a collection, thelen () function can calculate the size of any collection:

>>> Len (d) 3

Note: a key-value is counted one, so the dict size is 3.

Task

The new Paul students score is 75 points, please write a dict, the results of Paul's students also added in.

D = {    ' Adam ': +,    ' Lisa ': $,    ' Bart ': 59}
Reference code:
D = {
' Adam ': 95,
' Lisa ': 85,
' Bart ': 59,
' Paul ': 75

}

Python's visit to Dict

We have been able to create a dict that represents the correspondence between the name and the score:

D = {    ' Adam ': +,    ' Lisa ': $,    ' Bart ': 59}

So, how to find the corresponding score according to the name?

You can simply use the form of D[key] to find the corresponding value, which is like the list,but the list must return the corresponding element using the index, and Dict uses key:

>>> print d[' Adam ']95>>> print d[' Paul ']traceback (most recent call last):  File "index.py", line 11 , in <module>    print d[' Paul ']keyerror: ' Paul '

Note: The value of dict is accessed by key, and Dict returns the corresponding value as long as the key exists. If key does not exist, it will directly error: Keyerror.

There are two ways to avoid keyerror:

First, determine whether the key exists, with the in operator:

If ' Paul ' in D:    print d[' Paul '

If ' Paul ' is not present, the IF statement evaluates to False, and the print d[' Paul ' is not executed naturally, thus avoiding the error.

The second is to use the dict itself to provide a get method, when the key does not exist, return to none:

>>> print d.get (' Bart ') 59>>> print d.get (' Paul ') None

Task

According to the following dict:

D = {    ' Adam ': +,    ' Lisa ': $,    ' Bart ': 59}

Please print out:

adam:95lisa:85bart:59
Reference code:
D = {
' Adam ': 95,
' Lisa ': 85,
' Bart ': 59
}
For key in [' Adam ', ' Lisa ', ' Bart ']:
Print "%s:%d"% (key, D[key])

Or
D = {
' Adam ': 95,
' Lisa ': 85,
' Bart ': 59
}
Print "Adam:", D.get (' Adam ')
Print "Lisa:", d[' Lisa '
If ' Bart ' in D:
Print "Bart:", d[' Bart ')

What Python is Dict