Dict to List — How to Convert a Dictionary to a List in Python

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Summary: To convert a dictionary to a list of tuples, use the dict.items() method to obtain an iterable of (key, value) pairs and convert it to a list using the list(...) constructor: list(dict.items()). To modify each key value pair before storing it in the list, you can use the list comprehension statement [(k', v') for k, v in dict.items()] replacing k' and v' with your specific modifications.

In my code projects, I often find that choosing the right data structure is an important prerequisite to writing clean and effective code. In this article, you’ll learn the most Pythonic way to convert a dictionary to a list.

Problem: Given a dictionary of key:value pairs. Convert it to a list of (key, value) tuples.

Example: Given the following dictionary.

d = {'Alice': 19, 'Bob': 23, 'Carl': 47}

You want to convert it to a list of (key, value) tuples:

[('Alice', 19), ('Bob', 23), ('Carl', 47)]

You can get a quick overview of the methods examined in this article next:

Exercise: Change the data structure of the dictionary elements. Does it still work?

Let’s dive into the methods!

Method 1: List of Tuples with dict.items() + list()

dict to list python

The first approach uses the dictionary method dict.items() to retrieve an iterable of (key, value) tuples. The only thing left is to convert it to a list using the built-in list() constructor.

d = {'Alice': 19, 'Bob': 23, 'Carl': 47}

# Method 1
t = list(d.items())
print(t)
# [('Alice', 19), ('Bob', 23), ('Carl', 47)]

The variable t now holds a list of (key, value) tuples. Note that in many cases, it’s not necessary to actually convert it to a list, and, thus, instantiate the data structure in memory.

For example, if you want to loop over all (key, value) pairs in the dictionary, you can do so without conversion:

for k,v in d.items():
    s = str(k) + '->' + str(v)
    print(s)
'''
Alice->19
Bob->23
Carl->47
'''

Using the items() method on the dictionary object is the most Pythonic way if everything you want is to retrieve a list of (key, value) pairs. However, what if you want to get a list of keys—ignoring the values for now?

Method 2: List of Keys with dict.keys()

To get a list of key values, use the dict.keys() method and pass the resulting iterable into a list() constructor.

d = {'Alice': 19, 'Bob': 23, 'Carl': 47}

# Method 2
t = list(d.keys())
print(t)
# ['Alice', 'Bob', 'Carl']

Similarly, you may want to get a list of values.

Method 3: List of Values with dict.values()

To get a list of key values, use the dict.values() method and pass the resulting iterable into a list() constructor.

d = {'Alice': 19, 'Bob': 23, 'Carl': 47}

# Method 3
t = list(d.values())
print(t)
# [19, 23, 47]

But what if you want to modify each (key, value) tuple? Let’s study some alternatives.

Method 4: List Comprehension with dict.items()

List comprehension is a compact way of creating lists. The simple formula is [expression + context].

  • Expression: What to do with each list element?
  • Context: What elements to select? The context consists of an arbitrary number of for and if statements.

You can use list comprehension to modify each (key, value) pair from the original dictionary before you store the result in the new list.

d = {'Alice': 19, 'Bob': 23, 'Carl': 47}

# Method 4
t = [(k[:3], v-1) for k, v in d.items()]
print(t)
# [('Ali', 18), ('Bob', 22), ('Car', 46)]

You transform each key to a string with three characters using slicing and reduce each value by one.

Method 5: zip() with dict.keys() and dict.values()

Just for comprehensibility, you could (theoretically) use the zip() function to create a list of tuples:

d = {'Alice': 19, 'Bob': 23, 'Carl': 47}

# Method 5
t = list(zip(d.keys(), d.values()))
print(t)
# [('Alice', 19), ('Bob', 23), ('Carl', 47)]

However, there’s no benefit compared to just using the dict.items() method. However, I wanted to show you this because the zip() function is frequently used in Python and it’s important for you to understand it.

Method 6: Basic Loop

The last method uses a basic for loop—not the worst way of doing it! Sure, a Python pro would use the most Pythonic ways I’ve shown you above. But using a basic for loop is sometimes superior—especially if you want to be able to customize the code later (e.g., increasing the complexity of the loop body).

d = {'Alice': 19, 'Bob': 23, 'Carl': 47}

# Method 6
t = []
for k, v in d.items():
    t.append((k,v))
print(t)
# [('Alice', 19), ('Bob', 23), ('Carl', 47)]

A single-line for loop or list comprehension statement is not the most Pythonic way to convert a dictionary to a Python list if you want to modify each new list element using a more complicated body expression. In this case, a straightforward for loop is your best choice!

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Programmer Humor

❓ Question: Why do programmers always mix up Halloween and Christmas?
❗ Answer: Because Oct 31 equals Dec 25.

(If you didn’t get this, read our articles on the oct() and int() Python built-in functions!)

Where to Go From Here?

Enough theory. Let’s get some practice!

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