Lesson 5 - Dictionary

Dictionaries help in assigning a key for every value in the sequence.

citydict =

{
“city” : “Chicago”,
“population”, “2.8 million”,
“density” : 12000
}

print(citydict)

A dictionary is a collection which is ordered, changeable and do not allow duplicates.
Dictionaries are written with curly brackets, and have keys and values:

Duplicate keys are not allowed in dict, for example 

citydict =

{
“city” : “Chicago”,
“population”, “2.8 million”,
“density” : 12000
“density” ” 11000 // not allowed
}

Dictionary length

A dictionary length mean the number of items in it.
len(citydict) returns 3

Accessing a dictionary item using []

A dictionary item can be accessed using its key.

Example

x = citydict[“Population”]
print(x)  outputs “2.8 million”

Accessing a dictionary item using get function

Another way of accessing a dictionary item using get() function

Example

x = citydict.get(“Population”)
print(x)  outputs “2.8 million”

Getting all keys of dict

keys()  method returns all the keys of a dictionary

Getting all values of dict

values()  method returns all the values of a dictionary

Add a new item in the Dictionary

One can easily add a new item to an existing dictionary using the following syntax
For example you have a dictionary called report
report= { “subject”: “Maths”, “grade”:”A”, “marks” : 99}

And you want to add a new item called rank with a value of 7
report[“rank”] = 7

Check if the item is added or not
print(report) outputs {‘subject’: ‘Maths’, ‘grade’: ‘A’, ‘marks’: 99, ‘rank’: 7}

Change existing item in the Dictionary

To change an item , for example  marks from 99 to 97
report[“marks”] = 97   

or
report.update({“marks”: 97})

Remove an item from the Dictionary

There are several methods to remove an item. One such method is pop()
For example to remove rank  from the report

Emptying a dictionary

The clear() method empties the dictionary.
report.clear()

Nested dictionaries

A dictionary can contain another dictionary, this is called nested dictionaries.

For example student dictionary is inserted inside report