A dictionary is a collection that stores data in key/value pairs and is equivalent to a java map.  Keys can be of any immutable type.

Create

items = dict()
# or
items = {}

items['apple'] = 12
items['grape'] = 5
items['orange'] = 7

print(items)
{'apple': 12, 'grape': 5, 'orange': 7}

print(items['apple'])
12

otherItems = {'apple': 10, 'grape': 15, 'orange': 47}

Inspect

We can use the in operator to check if a key already exists

if 'apple' in items:
    # do something if apple exists

Retrieving Values

Retrieving a value for a key not contained in the dictionary will throw an error.  The dictionary get method returns a default value if the key is not contained in the dictionary.

x = items.get('carrot', 0)

Methods

  • items(): returns a list of key/value tuples
  • keys(): returns a list of keys
  • values(): returns a list of values

 

Functions

  • list(dictionary): returns a list of keys

 

Iteration

To iterate through a dictionary use the items method to obtain a list of tuples and iterate through the list using a for loop with two iteration variables:

for k, v in dictionary.items():
    print(k, v)