2017-10-15 610 views 评论

Python chapter 6 learning notes

l A simple dictionary

alien_0&nbsp;=&nbsp;{&#39;color&#39;:&nbsp;&#39;green&#39;,&#39;point&#39;:&nbsp;5}
print(alien_0[&#39;color&#39;])#使用大括号

1 2	alien_0 = {'color': 'green','point': 5} print(alien_0['color'])#使用大括号

The window will show green.

l Using dictionary

n Add key-value pair

For example,

alien_0&nbsp;=&nbsp;{&#39;color&#39;:&nbsp;&#39;green&#39;,&#39;point&#39;:&nbsp;5}
print(alien_0[&#39;color&#39;])
&nbsp;
alien_0[&#39;x_position&#39;]&nbsp;=&nbsp;0
alien_0[&#39;y_position&#39;]&nbsp;=&nbsp;25
print(alien_0)

alien_0 = {'color': 'green','point': 5}

print(alien_0['color'])

alien_0['x_position'] = 0

alien_0['y_position'] = 25

print(alien_0)

The window will show

{&#39;color&#39;:&nbsp;&#39;green&#39;,&nbsp;&#39;point&#39;:&nbsp;5,&nbsp;&#39;x_position&#39;:&nbsp;0,&nbsp;&#39;y_position&#39;:&nbsp;25}

1	{'color': 'green', 'point': 5, 'x_position': 0, 'y_position': 25}

Modify the key-value pair

alien_0[&#39;color&#39;]&nbsp;=&nbsp;&#39;yellow&#39;

1	alien_0['color'] = 'yellow'

Delete the key-value pair

Use del is OK.

For example,

del&nbsp;alien_0[&#39;points&#39;]

1	del alien_0['points']

Dictionary will not include points.

Dictionary just like struct in C language.
The dictionary which consists of many objects:

For example,

favorite_languages&nbsp;=&nbsp;{
&#39;David&#39;:&nbsp;&#39;python&#39;,
&#39;Jane&#39;&nbsp;:&nbsp;&#39;java&#39;,
&#39;John&#39;&nbsp;:&nbsp;&#39;C&#39;,
&#39;Sarah&#39;&nbsp;:&nbsp;&#39;ruby&#39;,
&#39;Michel&#39;&nbsp;:&nbsp;&#39;swift&#39;&nbsp;
}
&nbsp;
print(&quot;David&#39;s&nbsp;favorite&nbsp;languages&nbsp;is&nbsp;&quot;&nbsp;+&nbsp;
favorite_languages[&#39;David&#39;].title()&nbsp;+&nbsp;&quot;.&quot;)

favorite_languages = {

'David': 'python',

'Jane' : 'java',

'John' : 'C',

'Sarah' : 'ruby',

'Michel' : 'swift' 

}

print("David's favorite languages is " + 

favorite_languages['David'].title() + ".")

It will show,

David&#39;s&nbsp;favorite&nbsp;languages&nbsp;is&nbsp;Python.

1	David's favorite languages is Python.

Remember the format!

l Ergodic dictionary

n Ergodic all key-value pairs

Method: items(): items()方法用于返回字典dict的(key，value)元组对的列表

Ergodic all keys

Method: keys():返回字典dict的键列表

For example,

for&nbsp;name&nbsp;in&nbsp;favorite_languages.keys():
print(name.title()&nbsp;+&nbsp;&nbsp;&quot;.&quot;)
But&nbsp;if&nbsp;we&nbsp;use
for&nbsp;name&nbsp;in&nbsp;favorite_languages:
print(name.title()&nbsp;+&nbsp;&nbsp;&quot;.&quot;)

for name in favorite_languages.keys():

print(name.title() +  ".")

But if we use

for name in favorite_languages:

print(name.title() +  ".")

They all have same output.

n Ergodic all values

n Method: values():返回字典dict的值列表

As we all know, the list of value may have same values, then ,how to keep only one value?

We can use set(). For example,

for&nbsp;language&nbsp;in&nbsp;set(favorite_languages.values()):
print(language.title())

1 2	for language in set(favorite_languages.values()): print(language.title())

n Nesting: 将一系列字典存储在列表中，或将列表作为值存储在字典中，这被称为嵌套。

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