Functions and Methods Dictionaries Introduction

Dictionary

A dictionary is a collection which is unordered, changeable and indexed. In Python dictionaries are written with curly brackets, and they have keys and values.

Example

Create and print a dictionary:

thisdict =	{
  "brand": "Ford",
  "model": "Mustang",
  "year": 1964
}
print(thisdict)

Accessing Items

You can access the items of a dictionary by referring to its key name, inside square brackets:

Example

Get the value of the "model" key:

x = thisdict["model"]

There is also a method called get() that will give you the same result:

Example

Get the value of the "model" key:

x = thisdict.get("model")

Change Values

You can change the value of a specific item by referring to its key name:

Example

Change the "year" to 2018:

thisdict =	{
  "brand": "Ford",
  "model": "Mustang",
  "year": 1964
}
thisdict["year"] = 2018

Loop Through a Dictionary

You can loop through a dictionary by using a for loop.

When looping through a dictionary, the return value are the keys of the dictionary, but there are methods to return the values as well.

Example

Print all key names in the dictionary, one by one:

for x in thisdict:
  print(x)

Example

Print all values in the dictionary, one by one:

for x in thisdict:
  print(thisdict[x])

Example

You can also use the values() function to return values of a dictionary:

for x in thisdict.values():
  print(x) 

Example

Loop through both keys and values, by using the items() function:

for x, y in thisdict.items():
  print(x, y) 

Check if Key Exists

To determine if a specified key is present in a dictionary use the in keyword:

Example

Check if "model" is present in the dictionary:

thisdict =	{
  "brand": "Ford",
  "model": "Mustang",
  "year": 1964
}
if "model" in thisdict:
  print("Yes, 'model' is one of the keys in the thisdict dictionary") 

Dictionary Length

To determine how many items (key-value pairs) a dictionary has, use the len() method.

Example

Print the number of items in the dictionary:

print(len(thisdict)) 

Adding Items

Adding an item to the dictionary is done by using a new index key and assigning a value to it:

Example

thisdict =	{
  "brand": "Ford",
  "model": "Mustang",
  "year": 1964
}
thisdict["color"] = "red"
print(thisdict)