Definition of Dictionary:

Dictionary is the most flexible data type in python besides list.
Dictionaries can also be used to store multiple data, usually used to store information about an object.
 #The dictionary is an unordered data set and, when using the print function to output the dictionary,
#In general, the order of output is inconsistent with that of definition

Difference between dictionary and list:

Lists are ordered sets of objects and
 Dictionaries are unordered sets of objects and
 Dictionary defined with {}
Dictionaries use key value pairs to store data. Key value pairs are used to separate data
 Key key is index
 Value value is data
 Use between keys and values; separate
 The key must be unique (because we have to find the data through the key)
Value can take any data type, but key can only use string, number or tuple

View dictionary usage:

In [2]: xfl = {'name':'xuefeilong','age':18}

In [3]: type(xfl)   View type is dictionary type
Out[3]: dict

In [4]: xfl.   Many functions of dictionary are not commonly used
xfl.clear       xfl.items       xfl.pop         xfl.viewitems
xfl.copy        xfl.iteritems   xfl.popitem     xfl.viewkeys
xfl.fromkeys    xfl.iterkeys    xfl.setdefault  xfl.viewvalues
xfl.get         xfl.itervalues  xfl.update      
xfl.has_key     xfl.keys        xfl.values  

Define a dictionary:

# _*_ coding:utf-8 _*_
"""
file: dict_01.py
date:2018-07-15 10:53 AM
author: xfl
desc:

"""
# Define a dictionary
# A dictionary is an unordered collection of data. When print ing out a dictionary
# Usually not in the same order as the definition

xfl = {'name': 'xuefeilong',
       'age': 18,
       'height': 175,
       'weight': 66.5}
print xfl

Value from Dictionary:

# _*_ coding:utf-8 _*_
"""
file: dict_01.py
date:2018-07-15 10:53 AM
author: xfl
desc:

"""
# Define a dictionary
# A dictionary is an unordered collection of data. When print ing out a dictionary
# Usually not in the same order as the definition

xfl = {'name': 'xuefeilong',
       'age': 18,
       'height': 175,
       'weight': 66.5}
# print xfl

# 1. value
print xfl['height']

Modify the dictionary value:

# _*_ coding:utf-8 _*_
"""
file: dict_01.py
date:2018-07-15 10:53 AM
author: xfl
desc:

"""
# Define a dictionary
# A dictionary is an unordered collection of data. When print ing out a dictionary
# Usually not in the same order as the definition

xfl = {'name': 'xuefeilong',
       'age': 18,
       'height': 175,
       'weight': 66.5}
# print xfl
# 2. Add / modify
xfl['age'] = 21  # Replace key directly when it exists
print xfl
xfl['sex'] = 'man'  # Add directly when the key does not exist
print xfl

To delete a dictionary element:

xfl = {'name': 'xuefeilong',
       'age': 18,
       'height': 175,
       'weight': 66.5}

# 3. delete
xfl.pop('name')
print xfl

There is no extend in the dictionary usage, and errors will be reported when using. Don't confuse the concept:

a=[1,2,3,4,5]

b=[6,7,8]

print a.extend(b)

len count the number of key value pairs:

xfl = {'name': 'xuefeilong',
       'age': 18,
       'height': 175,
       'weight': 66.5}
print xfl
# 1. Count the number of key value pairs
print len(xfl)

update merge Dictionary:

xfl = {'name': 'xuefeilong',
       'age': 18,
       'height': 175,
       'weight': 66.5}
print xfl
# 2. Merge dictionary
# The dictionary's custom key is variable and unique
xyy = {'name': 'xiangyuanyuan',
       # Existing key direct substitution
       'sex': 'girl'}
       # Non existent key added directly
xfl.update(xyy)
print xfl

Cycle key value:

# _*_ coding:utf-8 _*_
"""
file: dict_03.py
date:2018-07-15 11:35 AM
author: xfl
desc:

"""
# Simply loop a key value
xfl = {'name': 'xuefeilong',
       'age': 18,
       'height': 175,
       'weight': 66.5}
for k in xfl:
    print '%s ----> %s' % (k, xfl[k])
# xfl[k] is output by K to index the corresponding value

Circular Dictionary:

# _*_ coding:utf-8 _*_
"""
file: dict_04.py
date:2018-07-15 11:37 AM
author: xfl
desc:

"""
# Loop a dictionary in the form of a list (loop the dictionary by putting it in the list)
card_list = [{'name': 'xfl', 'age': '18'},
             {'name': 'xyy', 'age': '21'}]
for card_info in card_list:
    for k in card_info:  # Using nesting to output the value of each dictionary
        print '%s ----> %s' % (k, card_info[k])