Three methods for creating a Python dictionary

If you have any questions about how to create a Python dictionary and how to access the values in the dictionary, you can browse our article, after reading this article, I hope you will learn something from it. The following describes the specific content of this article.

Create a Python dictionary

Method ①:

 
 

  
  
>>> dict1 = {}  
  
  
>>> dict2 = {'name': 'earth', 'port': 80}  
  
  
>>> dict1, dict2  
  
  
({}, {'port': 80, 'name': 'earth'})  
 
 

Method 2: Start With Python 2.2

 
 

  
  
>>> fdict = dict((['x', 1], ['y', 2]))  
  
  
>>> fdict  
  
  
{'y': 2, 'x': 1}  
 
 

Method ③: from Python 2.3, you can use a convenient built-in method fromkeys () to create a "default" dictionary. The elements in the dictionary have the same value (if not given, the default value is None ):

 
 

  
  
>>> ddict = {}.fromkeys(('x', 'y'), -1)  
  
  
>>> ddict  
  
  
{'y': -1, 'x': -1}  
  
  
>>> 
  
  
>>> edict = {}.fromkeys(('foo', 'bar'))  
  
  
>>> edict  
  
  
{'foo': None, 'bar': None}  
 
 

How to access values in the dictionary

① To traverse a dictionary (usually using a key), you only need to view its key cyclically, as shown in the following code:

 
 

  
  
>>> dict2 = {'name': 'earth', 'port': 80}  
  
  
>>> 
  
  
>>>> for key in dict2.keys():  
  
  
... print 'key=%s, value=%s' % (key, dict2[key])  
  
  
...  
  
  
key=name, value=earth 
  
  
key=port, value=80 
 
 

② Traverse the dictionary in the for loop from Python 2.2.

 
 

  
  
>>> dict2 = {'name': 'earth', 'port': 80}  
  
  
>>> 
  
  
>>>> for key in dict2:  
  
  
... print 'key=%s, value=%s' % (key, dict2[key])  
  
  
...  
  
  
key=name, value=earth 
  
  
key=port, value=80 
 
 

To get the value of an element in the Python dictionary, you can use the dictionary key you are familiar with and brackets to get it:

 
 

  
  
>>> dict2['name']  
  
  
'earth'  
  
  
>>> 
  
  
>>> print 'host %s is running on port %d' % \  
  
  
... (dict2['name'], dict2['port'])  
  
  
host earth is running on port 80  
 
 

③ Dictionary all methods. Methods has_key (), in, and not in are boolean operators.

 
 

  
  
>>> 'Server' in dict2 # Or dict2.has _ key ('server ')
  
  
False
  
  
>>> 'Name' in dict # Or dict2.has _ key ('name ')
  
  
True
  
  
>>> Dict2 ['name']
  
  
'Global'
 
 

An example of mixing numbers and strings in a dictionary:

 
 

  
  
>>> dict3 = {}  
  
  
>>> dict3[1] = 'abc'  
  
  
>>> dict3['1'] = 3.14159  
  
  
>>> dict3[3.2] = 'xyz'  
  
  
>>> dict3  
  
  
{3.2: 'xyz', 1: 'abc', '1': 3.14159}  
 
 

The above article introduces how to apply the Python dictionary and how to access the values in the dictionary.