9-Dictionary

Notebook

Link to the Google Colaboratory notebook: 9-Dictionary

Dictionaries are used to store data values in key:value pairs.

thisdict = {
  "city": "Evry",
  "model": "Linear Regression",
  "year": 1977
}

Length

You can access the number of pairs of (key, value) with the len command:

example_dict = {
  "city": "Evry",
  "model": "Linear Regression",
  "year": 1977
}
print(len(example_dict))

To get the content of a dictionary, you need to know a specific key. Given a key, you can access the value:

content = {"name": "Evry"}
print(content["name"])
# You can also use the `.get` 
print(content.get("name"))

Evry
Evry

You can also list the elements of the dictionary using .keys() command:

example_dict = {
  "city": "Evry",
  "model": "Linear Regression",
  "year": 1977
}
print(example_dict.keys())

dict_keys(['city', 'model', 'year'])

You can also access the value of a dictionary with the .values() command:

print(example_dict.values())

dict_values(['Evry', 'Linear Regression', 1977])

You can access both the values and the keys with the .items command.

Note that it will return a tuple of (key, value):

print(example_dict.items())

dict_items([('city', 'Evry'), ('model', 'Linear Regression'), ('year', 1977)])

You can check if an element is in the keys of a dictionary:

example_dict = {
  "city": "Evry",
  "model": "Linear Regression",
  "year": 1977
}

print("a" in example_dict)
print("city" in example_dict)

False
True

The update() method will update the dictionary with the items from the given argument.

The argument must be a dictionary with the updated {key: value}.

example_dict = {
  "city": "Evry",
  "model": "Linear Regression",
  "year": 1977
}

example_dict.update({"year" : 77})
print(example_dict)

{'city': 'Evry', 'model': 'Linear Regression', 'year': 77}

You can also add an element to a dictionary by just refering the new key as following:

example_dict = {"test": -1}
example_dict["new_key"] = "new_value"
print(example_dict)

{'test': -1, 'new_key': 'new_value'}

You can remove an element of the dictionary using the pop function:

example_dict = {
  "city": "Evry",
  "model": "Linear Regression",
  "year": 1977
}
example_dict.pop("year")
print(example_dict)

{'city': 'Evry', 'model': 'Linear Regression'}

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.

Print keys

for key in example_dict:
    print(key)
for key in example_dict.keys():
    print(key)

city
model
city
model

Print values

for key in example_dict:
    print(example_dict[key])
for key in example_dict.values():
    print(key)

Evry
Linear Regression
Evry
Linear Regression

You can also iterate with both the keys and the values using the items command:

for key, value in example_dict.items():
    print(key, value)

city Evry
model Linear Regression