Dictionaries

Dictionaries are unordered set of key value pairs separated by commas. Unlike Lists (which are sequence based) dictionary elements are not indexed but can be retrieved using the keys.

Creating Dictionaries



In [31]:

    
# Starting with Empty Dictionary
dict1 = {}
dict1['id'] = 1
dict1['name'] = 'Hello'
dict1









    Out[31]:





{'id': 1, 'name': 'Hello'}



In [32]:

    
# Direct Method
dict2 = {'id':2,'name':'John'}
dict2









    Out[32]:





{'id': 2, 'name': 'John'}



In [29]:

    
# Using List of Tuples
dict3 = dict([('id',1),('name','Donald')])
dict3









    Out[29]:





{'id': 1, 'name': 'Donald'}



In [30]:

    
# Using Key-Value arguments
dict4 = dict(id=1,name='Tim')
dict4









    Out[30]:





{'id': 1, 'name': 'Tim'}

Adding, Editing, Removing Elements



In [10]:

    
# adding a key/value pair
dict4['salary'] = 71500.75
dict4









    Out[10]:





{'id': 1, 'name': 'Tim', 'salary': 71500.75}



In [11]:

    
# removing a key
del dict4['salary']
dict4









    Out[11]:





{'id': 1, 'name': 'Tim'}



In [12]:

    
# updating a key
dict4['name'] = 'Tim Billy'
dict4









    Out[12]:





{'id': 1, 'name': 'Tim Billy'}



In [54]:

    
# count the number of elements
len(dict4)









    Out[54]:





2

Checking for Keys



In [13]:

    
# Check if salary key exists
if 'salary' in dict4:
    print(dict4['salary'])
else:
    print(0)



In [36]:

    
# Better way of checking
print(dict4.get('name'))
print(dict4.get('salary')) # returns None if key is not present









    



Tim
None

Looping Techniques



In [18]:

    
# Default Method
for key in dict4:
    print(dict4[key])









    



1
Tim Billy



In [19]:

    
# Using Keys Method
for key in dict4.keys():
    print(dict4[key])









    



1
Tim Billy



In [20]:

    
# Using Values Method
for value in dict4.values():
    print(value)









    



1
Tim Billy



In [21]:

    
# Using Items Method
for k,v in dict4.items():
    print('{}:{}'.format(k,v))









    



id:1
name:Tim Billy

Dictionary Comprehensions



In [22]:

    
{x: x**2 for x in range(10)}









    Out[22]:





{0: 0, 1: 1, 2: 4, 3: 9, 4: 16, 5: 25, 6: 36, 7: 49, 8: 64, 9: 81}

Dictionary Methods



In [44]:

    
# copy
dict5 = dict4.copy()
dict5['name']='Billy John'
print(dict4)
print(dict5)









    



{'id': 1, 'name': 'Tim'}
{'id': 1, 'name': 'Billy John'}



In [42]:

    
# merge 2 dictionaries
knowledge = {"Frank": {"Perl"}, "Monica":{"C","C++"}}
knowledge2 = {"Guido":{"Python"}, "Frank":{"Perl", "Python"}}
knowledge.update(knowledge2)
knowledge









    Out[42]:





{'Frank': {'Perl', 'Python'}, 'Guido': {'Python'}, 'Monica': {'C', 'C++'}}



In [41]:

    
# remove all elements from the dictionary

print(dict1)
dict1.clear()
print(dict1) # pls note dictionary is not deleted but only emptied









    



{'id': 1, 'name': 'Hello'}
{}

Lists to Dictionaries



In [51]:

    
countries = ['United States','England','France','India']
capitals = ['Washington','London','Paris','New Delhi']
country_capital_zip = zip(countries,capitals) # returns list iterator
print(dict(country_capital_zip))
country_capitals = list(zip(countries,capitals))
print(country_capitals)
print(dict(country_capitals))









    



{'United States': 'Washington', 'England': 'London', 'France': 'Paris', 'India': 'New Delhi'}
[('United States', 'Washington'), ('England', 'London'), ('France', 'Paris'), ('India', 'New Delhi')]
{'United States': 'Washington', 'England': 'London', 'France': 'Paris', 'India': 'New Delhi'}



In [52]:

    
# combined to single step
country_specialities_dict = dict(list(zip(["pizza", "sauerkraut", "paella", "hamburger"], ["Italy", "Germany", "Spain", "USA"," Switzerland"])))
print(country_specialities_dict)









    



{'pizza': 'Italy', 'sauerkraut': 'Germany', 'paella': 'Spain', 'hamburger': 'USA'}

Dictionary with other Data Types



In [4]:

    
dict6 = {'name':'Alex','favorite_colors':['Blue','Red'],'contacts':{'email':'alex@example.com','phone':'123-456-7890'},'nick_names':('Alexie','A-man')}
dict6
print(dict6['favorite_colors'])
print(dict6['contacts']['email'])
print(dict6['nick_names'])









    



['Blue', 'Red']
alex@example.com
('Alexie', 'A-man')