Python chapter 6 learning notes

l  A simple dictionary

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 = {'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

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

• Modify the key-value pair

alien_0['color'] = 'yellow'

• Delete the key-value pair

Use del is OK.

For example,

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 = {
'David': 'python',
'Jane' : 'java',
'John' : 'C',
'Sarah' : 'ruby',
'Michel' : 'swift' 
}
 
print("David's favorite languages is " + 
favorite_languages['David'].title() + ".")

It will show,

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 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 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。