5 Best Ways to Convert Python Lists to Dictionary Values

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💡 Problem Formulation: In Python programming, developers often need to convert a list into a dictionary, where list elements become the values associated with some corresponding keys. For instance, given a list ['apple', 'banana', 'cherry'], one might want to create a dictionary where these fruits are values for keys 1, 2, and 3 respectively, resulting in {1: 'apple', 2: 'banana', 3: 'cherry'}.

Method 1: Using enumerate() Function

This method involves the built-in enumerate() function, which returns an iterable yielding pairs of index and list value. The dictionary is then constructed by mapping each index to its corresponding list value using a dictionary comprehension. It’s particularly useful when you want to start indexing from a number other than 0.

Here’s an example:

fruits = ['apple', 'banana', 'cherry']
dict_fruits = {i: fruit for i, fruit in enumerate(fruits, 1)}
print(dict_fruits)

Output:

{1: 'apple', 2: 'banana', 3: 'cherry'}

This snippet creates a dictionary from the list of fruits with indices starting at 1. The enumerate() function allows specifying the starting index, and the dictionary comprehension constructs the dictionary.

Method 2: Using zip() Function with Keys

When you have a separate list of keys and you want to pair them with a list of values, the zip() function comes in handy to stitch them together into a dictionary.

Here’s an example:

keys = [1, 2, 3]
values = ['apple', 'banana', 'cherry']
dict_fruits = dict(zip(keys, values))
print(dict_fruits)

Output:

{1: 'apple', 2: 'banana', 3: 'cherry'}

This code combines the keys and values into pairs using zip() and then converts the iterable of pairs into a dictionary using the dict() constructor.

Method 3: Using dict.fromkeys() Function

The dict.fromkeys() method can be used when the same value is to be assigned for each key in the dictionary. This is suitable for initializing dictionary values.

Here’s an example:

keys = [1, 2, 3]
value = 'fruit'
dict_fruits = dict.fromkeys(keys, value)
print(dict_fruits)

Output:

{1: 'fruit', 2: 'fruit', 3: 'fruit'}

This code creates a dictionary where all keys (from the list) are associated with the same value ‘fruit’ using the fromkeys() method.

Method 4: Using a For Loop with Indexing

If you need full control over the transformation process, using a for loop with manual indexing can be the simplest and most explicit approach.

Here’s an example:

values = ['apple', 'banana', 'cherry']
dict_fruits = {}
for index, value in enumerate(values):
    dict_fruits[index + 1] = value
print(dict_fruits)

Output:

{1: 'apple', 2: 'banana', 3: 'cherry'}

This code manually iterates through the list, assigning each value to its corresponding index as a key in the dictionary, thereby converting the list into dictionary values.

Bonus One-Liner Method 5: Using Dictionary Comprehension with Range

In a one-liner fashion, dictionary comprehension can be used with the range() function to create keys that correspond to the list indices.

Here’s an example:

values = ['apple', 'banana', 'cherry']
dict_fruits = {index + 1: value for index, value in enumerate(values)}
print(dict_fruits)

Output:

{1: 'apple', 2: 'banana', 3: 'cherry'}

This one-liner uses dictionary comprehension with enumerate() to merge indices and values into a dictionary directly.

Summary/Discussion

  • Method 1: Using enumerate(). Strength: Convenient indexing. Weakness: Limited to linear indexing.
  • Method 2: Using zip() with keys and values. Strength: Flexible with pre-defined keys. Weakness: Requires separate keys list.
  • Method 3: Using dict.fromkeys(). Strength: Instant bulk value assignment. Weakness: Single value used for all keys.
  • Method 4: For loop with indexing. Strength: Explicit control. Weakness: More verbose and less Pythonic.
  • Method 5: Dictionary comprehension with range(). Strength: Elegant one-liner. Weakness: May be less readable for beginners.