How can I get list of values from dict?

python

data-structures

collections

performance

byAnton Shumikhin·Aug 23, 2024

To retrieve values from a dictionary as a list, use list(dict.values()). For example:

# No diploma needed! It's as simple as this.
dict_values = list({'a': 1, 'b': 2}.values())
print(dict_values)  # outputs [1, 2]

Exploring different collection types

Depending on your use case, you might prefer using collection types other than lists for your values:

Using `set` for unique values

A set is useful if you are looking for unique values:

unique_values = set(your_dict.values())

Using `tuple` for an immutable collection

A tuple is your go-to if you need an immutable collection:

immutable_values = tuple(your_dict.values())

Dynamic nature of the `values()` method

What happens if your dictionary changes after you've retrieved its values? Well, dict.values() returns a dynamic view on the dictionary's values. This view changes when the dictionary changes.

Dynamic `values()` method in practice

# Define a dictionary.
d = {'a': 1, 'b': 2}
# Get a view on the dictionary's values.
values_view = d.values()
# Add another key-value to the dictionary.
d['c'] = 3
# See what happened to your values. Surprised?
print(values_view)  # dict_values([1, 2, 3])

Consider the speed: efficiency matters

The performance of your Python script can be influenced by the size of your dictionary and your specific environment.

Timing is everything: measuring with `timeit`

# When speed matters... test it!
import timeit
timeit.timeit("list(d.values())", globals={'d': your_dict})

Flexibility in value extraction

For more complex scenarios, where values are to be manipulated, list comprehensions or map with lambda may come in handy.

Filtering with list comprehension

# Only the evens! We work 9 to 5 around here.
even_values = [val for val in your_dict.values() if val % 2 == 0]

Transforming values with `map` and `lambda`

# Sneakily adding 1 to every value. Don't tell anyone!
incremented_values = list(map(lambda x: x + 1, your_dict.values()))

Extracting values for specific keys

When you want to extract values of specific keys, itemgetter() becomes your best friend.

Efficiency with `itemgetter()`

from operator import itemgetter
# Just like asking for directions!
keys = ['a', 'c']
values = itemgetter(*keys)(your_dict)

Embrace data structures per use-case

Different use cases call for different data structures. Considering them can make a noticeable difference.

Default values with `defaultdict`

# Guarantees that no one goes without!
from collections import defaultdict
d = defaultdict(int)
d['a'] += 1

Maintaining insertion order with `OrderedDict`

# Remembering the order of things. What were we talking about again?
from collections import OrderedDict
od = OrderedDict([('a', 1), ('b', 2)])

Platform specifics do matter

What works best on one platform might not on another. Software and hardware environments influence the performance. Hence, it's always best to test in your specific setting.