Python chapter 6 learning notes

  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。