Python Create List from Dict Keys (5 Methods) : Chris
by: Chris
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Problem Formulation: Python dictionaries store data as key-value pairs. Sometimes, e.g., for the purpose of iteration or other operations, we may want to create a list out of just the keys from a dictionary.
Let’s explore some methods to do this, using a simple dictionary as an example:
sample_dict = {"apple": 1, "banana": 2, "cherry": 3}
Our goal is to create a list: ["apple", "banana", "cherry"]
.
Method 1: Using list()
The list()
constructor is the most straightforward approach to convert the dictionary keys into a list. By default, iterating a dictionary gives you its keys, so you can wrap it with list()
.
Code example:
keys_list = list(sample_dict) print(keys_list) # Output: ['apple', 'banana', 'cherry']
Here, list(sample_dict)
converts the dictionary keys into a list.
Dict to List — How to Convert a Dictionary to a List in Python
Method 2: Using dict.keys()
The dict.keys()
method returns a view object that displays a list of all the keys. When you wrap it with list()
, it converts that view into a list.
Code example:
keys_list = list(sample_dict.keys()) print(keys_list) # Output: ['apple', 'banana', 'cherry']
This will explicitly fetch the keys using sample_dict.keys()
and then convert them to a list.
How to Return Dictionary Keys as a List in Python?
Method 3: Using a for loop
If you need more control over the process, you can iterate through the dictionary with a for
loop and append each key to a new list.
Code example:
keys_list = [] for key in sample_dict: keys_list.append(key) print(keys_list) # Output: ['apple', 'banana', 'cherry']
The for
loop goes through each key in the dictionary and appends each to keys_list
.
Python Get List of Values from List of Keys
Method 4: Using List Comprehension
List comprehension is a concise way to achieve the same result as the for loop, but in a single, readable line.
Code example:
keys_list = [key for key in sample_dict] print(keys_list) # Output: ['apple', 'banana', 'cherry']
This line creates a new list, iterating through sample_dict
and adding each key
into the keys_list
.
Can a Python Dictionary Have a List as a Value?
Method 5: Using map()
The map()
function can also be used to create a list of keys, although not as straight-to-the-point as the other methods.
Code example:
keys_list = list(map(lambda k: k, sample_dict)) print(keys_list) # Output: ['apple', 'banana', 'cherry']
This utilizes a lambda
function that simply returns the key and maps it across the sample_dict
, then converts the result to a list.
Bonus One-Liner Method 6: Using * Operator
With Python 3.5 and later, you can use the *
operator, also known as the unpacking operator, within a list literal.
Code example:
keys_list = [*sample_dict] print(keys_list) # Output: ['apple', 'banana', 'cherry']
Here the *
operator unpacks the keys from sample_dict
directly into the list literal, creating keys_list
.
Summary/Discussion
Creating a list from dictionary keys in Python can be done with several techniques ranging from simple, such as using list()
, to more explicit ways, like iterating with a loop or comprehension.
Each method has its perks in different contexts, but they all effectively solve the problem. Whether you need a one-liner or a more customized solution, Python offers a rich set of tools for working with dictionaries and lists.
February 05, 2024 at 11:49PM
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