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Python Dictionaries

In python, a dictionary is a mixed and unordered collection of data values. The dictionary type stores a key along with its value, where the keys are unique within a collection and the values can hold any arbitrary value. The values in dictionaries are changeable and it does not allow duplicates.

Creating a Dictionary

A Dictionary is created with curly brackets{}, it contains keys and values, to separate each key from its value single colon(:) is used. Each key and value is separated by comma.

Example:

my_dict = {
           "Name" : "Ram", 
           "Department" : "BCA", 
           "Year" : "3ed"
}

print(my_dict)
print(type(my_dict))

Output:

{'Name': 'Ram', 'Department': 'BCA', 'Year': '3ed'}
<class 'dict'>

We can also create a dictionary using dict() method,

Example:

my_dict = dict([("Name", "Ram"), ("Department" , "BCA"), ("Year" , "3ed")])
print(my_dict)
print(type(my_dict))

Output:

{'Name': 'Ram', 'Department': 'BCA', 'Year': '3ed'}
<class 'dict'>

Access Elements in Dictionary

Dictionaries are indexed using their keys, so we can access a particular value in a dictionary using key inside square brackets.

Example:

my_dict = {"Name" : "Ram", "Department" : "BCA", "Year" : "3ed"}
print(my_dict["Name"], "is from", my_dict["Department"], "department")

Output:

Ram is from BCA department

Updating Dictionary

Dictionaries can be updated directly using the keys or using the update() method.

Example using keys:

my_dict = {"Name" : "Ram", "Department" : "BCA", "Year" : "3ed"}
my_dict["Name"] = "Murali"
print(my_dict)

Output:

{'Name': 'Murali', 'Department': 'BCA', 'Year': '3ed'}

Example using update() method:

my_dict = {"Name" : "Ram", "Department" : "BCA", "Year" : "3ed"}
my_dict.update({"Name" : "Murali"})
print(my_dict)

Output:

{'Name': 'Murali', 'Department': 'BCA', 'Year': '3ed'}

Adding values

We can add a element in a dictionary by dict[key] = value.

Example:

my_dict = {"Name" : "Ram", "Department" : "BCA", "Year" : "3ed"}
my_dict["Semester"] = "5th"
print(my_dict)

Output:

{'Name': 'Ram', 'Department': 'BCA', 'Year': '3ed', 'Semester': '5th'}

Remove Dictionary Elements

There are several methods to remove items from a dictionary. You can either remove individual dictionary elements or clear the entire contents of a dictionary.

del keyword

Using del keyword, we can remove a specific values from a dictionary as well as we can delete whole dictionary.

Example:

#Delete specific value
my_dict = {"Name" : "Ram", "Department" : "BCA", "Year" : "3ed"}
del my_dict["Year"]
print(my_dict)

#Delete entire dictionary
my_dict = {"Name" : "Ram", "Department" : "BCA", "Year" : "3ed"}
del my_dict
print(my_dict)

Output:

Delete specific value
:
{'Name': 'Ram', 'Department': 'BCA'}

Delete entire dictionary
:
Traceback (most recent call last):
  File "dictn.py", line 4, in <module>
    print(my_dict)
NameError: name 'my_dict' is not defined

Using pop() method

pop() method will remove the value of the key specified.

Example:

my_dict = {"Name" : "Ram", "Department" : "BCA", "Year" : "3ed"}
my_dict.pop("Department")
print(my_dict)

Output:

{'Name': 'Ram', 'Year': '3ed'}

Using popitem() method

popitem() method will remove the lastly inserted item.

Example:

my_dict = {"Name" : "Ram", "Department" : "BCA", "Year" : "3ed"}
my_dict.popitem()
print(my_dict)

Output:

{'Name': 'Ram', 'Department': 'BCA'}

Other Built-in Dictionary methods

get() method

get() method is used access a value for a key.

Example:

my_dict = {"Name" : "Ram", "Department" : "BCA", "Year" : "3ed"}
print(my_dict.get("Name"))

Output:

Ram

keys() method

keys() method will return all the keys in the dictionary.

Output:

my_dict = {"Name" : "Ram", "Department" : "BCA", "Year" : "3ed"}
print(my_dict.keys())

Output:

dict_keys(['Name', 'Department', 'Year'])

values() method

values() method will return all the values in the dictionary.

Output:

my_dict = {"Name" : "Ram", "Department" : "BCA", "Year" : "3ed"}
print(my_dict.values())

Output:

dict_values(['Ram', 'BCA', '3ed'])

items() method

items() method will return all the key and value pairs in the dictionary.

Example:

my_dict = {"Name" : "Ram", "Department" : "BCA", "Year" : "3ed"}
print(my_dict.items())

Output:

dict_items([('Name', 'Ram'), ('Department', 'BCA'), ('Year', '3ed')])

clear() method

clear() method will remove all the items from the dictionary.

Output:

my_dict = {"Name" : "Ram", "Department" : "BCA", "Year" : "3ed"}
my_dict.clear()
print(my_dict)

Output:

{}

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