Python Dictionary

Creating Python Dictionary

A dictionary is a data structure allowing to have access to a set of data. It is used to have variables with their correspondences. However, the difference between a dictionary and a list is that the bracket delimiter and the indexes of lists are replaced by braces and keys in dictionaries. To create a dictionary, you need two elements which are the keys and the values separated by a colon. Keys and values can be in different type.There are several methods to build a dictionary. The syntaxes are written as follows:

 #create dictionary
 dict = {}
 #Or
 dict = {'keys':'values', 'keys':'values','keys':'values'}

A key can have values as a list or as a dictionary. In both cases, the creation of the dictionary is done as follows:

 #dictionary of dictionairies
 dict ={'keys':{'keys': 'values', 'keys':'values', 'keys':'values'}}
 
 #dictionary with value as a list
 dict_list={'keys':['...','...','...']}

Verification element in the dictionary

The verification of keys, values in any dictionary is done respectively by these methods. They are written as follows in the lines of code below:

# print Keys
 'Keys'in dict
 
 # Print out value that belong to 'keys'
 print(dict['keys'])

Deleting

Delete a key in a dictionary is done in the same way as in a list.

#delete keys
 del(dict['keys'])

The method of adding a new element to a dictionary is identical to the method of updating it. The code below illustrates this in detail:

#add new element
 Dict['keys'] ='values'

Merge dictionaries

The merging of two dictionaries is done with .update(). The code below tells us this:

 # creating two new dictionary
 dict_1 ={}
 dict_2 ={}
 
 # merge of dictionaries
 dict_1. update (Dict_2)
 print(dict_1)

Concrete example

In this practical case, we would create a dictionary and perform the operations seen above. Our dictionary contains information about the price of foodstuffs in Senegal.

 #create dictionary
 dict_food ={'rice':350, 'oil':150,'sugar':650,'milk':100}
 
 # delete ‘milk’
 del(dict_food['milk'])
 
 #add new keys
 dict_food['corn'] =300
 print(dict_food)
 output:
 {'rice': 350, 'oil': 150, 'sugar': 650, 'corn': 300}
 
 # another dictionary
 dict_sen = {'tomate':1000,'oignon':500,'Pomme de terre':500}
 
 #merging dict_food and dict_sen
 dict_food.update(dict_sen)
 print(dict_food)
 output:
 {'rice': 350, 'oil': 150, 'sugar': 650, 'corn': 300, 'tomate': 1000, 'oignon': 500, 'potatos': 500}