Dictionaries

Object views and iterating over dictionaries

In this Python lesson, you'll explore object views, dynamic representations of a dictionary's keys, values, or items, and learn how to use them to iterate over dictionaries.

Let's create a new dictionary that we can work with:

capitals = {
  'USA': 'Washington D.C.',
  'France': 'Paris',
  'Brazil': 'Brasília',
  'Peru': 'Lima'
}

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Sometimes, you'll need to extract the keys from a dictionary.

You can do so using the dict.keys() method.

capitals = {
  'USA': 'Washington D.C.',
  'France': 'Paris',
  'Brazil': 'Brasília',
  'Peru': 'Lima'
}
 
keys = capitals.keys()
 
print(keys)

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Output

The dict.keys() method returns a so-called view object.

This view object provides a dynamic view of the dictionary's keys.

It's dynamic because it reflects changes made to the dictionary in real-time.

Here we add a new key after creating the view object.

capitals = {
  'USA': 'Washington D.C.',
  'France': 'Paris',
  'Brazil': 'Brasília',
  'Peru': 'Lima'
}
 
keys = capitals.keys()
 
print(keys)
 
# add new key-value pair
capitals['Germany'] = 'Berlin'
 
print(keys)

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Output

Notice that the new key has been added to the view object.

You can transform the view object into a static list using the list() function:

capitals = {
  'USA': 'Washington D.C.',
  'France': 'Paris',
  'Brazil': 'Brasília',
  'Peru': 'Lima'
}
 
keys = capitals.keys()
 
# transform view object into list
print(list(keys))

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Output

If you want to extract a dictionary's values instead of its keys, you can use the dict.values() method:

capitals = {
  'USA': 'Washington D.C.',
  'France': 'Paris',
  'Brazil': 'Brasília',
  'Peru': 'Lima'
}
 
values = capitals.values()
 
print(values)

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Output

Another view object method is dict.items(), which returns a dynamic view of all key-value pairs in a dictionary:

capitals = {
  'USA': 'Washington D.C.',
  'France': 'Paris',
  'Brazil': 'Brasília',
  'Peru': 'Lima'
}
 
items = capitals.items()
 
print(items)

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Output

What will be the output?

my_dict = { 'a': 1, 'b': 2 }
 
print(my_dict.keys())

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What will be the output?

my_dict = { 'a': 1, 'b': 2 }
 
print(my_dict.values())

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What will be the output?

my_dict = { 'a': 1, 'b': 2 }
 
print(my_dict.items())

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Sometimes it's necessary to iterate over keys, values or key-value pairs in dictionaries.

We can accomplish this using a for-loop and the view objects introduced earlier.

Here, we iterate over the values of our dictionary:

capitals = {
  'USA': 'Washington D.C.',
  'France': 'Paris',
  'Brazil': 'Brasília',
  'Peru': 'Lima'
}
 
# loop over values
for value in capitals.values():
  print(value)

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Output

We don't need to use a view object to iterate over the keys of our dictionary:

capitals = {
  'USA': 'Washington D.C.',
  'France': 'Paris',
  'Brazil': 'Brasília',
  'Peru': 'Lima'
}
 
# loop over keys
for key in capitals:
  print(key)

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Output

With dict.items() we can iterate over keys and values simultaneously:

capitals = {
  'USA': 'Washington D.C.',
  'France': 'Paris',
  'Brazil': 'Brasília',
  'Peru': 'Lima'
}
 
# loop over key-value pairs
for key, value in capitals.items():
  print('The capital of', key, 'is', value)

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Output

What will be the output?

my_dict = { 'a': 'x', 'b': 'y' }
 
for key in my_dict:
  print(key)

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What will be the output?

my_dict = { 'a': 'x', 'b': 'y' }
 
for value in my_dict.values():
  print(value)

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What will be the output?

my_dict = { 'a': 'x', 'b': 'y' }
 
for key, value in my_dict.items():
  print(key+value)

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