Python Create Dictionary with Integer

The task of creating a dictionary from a list of keys in Python, where each key is assigned a unique integer value, involves transforming the list into a dictionary. Each element in the list becomes a key and the corresponding value is typically its index or a different integer.

For example, if we have a list like ['apple', 'banana', 'orange'], the goal is to convert it into a dictionary like {'apple': 0, 'banana': 1, 'orange': 2}, where each key is paired with a distinct integer.

Using dictionary comprehension

Dictionary comprehension is a efficient way to create dictionaries by iterating over an iterable. When used to create a dictionary with integers, we can pair each key with a unique integer, such as using the index of the element. This method is both readable and fast, making it one of the most Pythonic approaches for this task.

li = ['apple', 'banana', 'orange']

d = {key: idx for idx, key in enumerate(li)}
print(d)

{'apple': 0, 'banana': 1, 'orange': 2}

Explanation: enumerate() generates index-value pairs from the list li , where the element is the key and its idx is the value. The dictionary comprehension then iterates over these pairs, creating a dictionary where each list element is mapped to its corresponding index.

Using dict(zip())

zip() pairs two iterables element-wise and when combined with dict(), it creates a dictionary. This method is particularly useful when we want to pair each element from a list with an index from a generated range. It’s an elegant solution for creating a dictionary with unique integer values as the keys.

li = ['apple', 'banana', 'orange']

d = dict(zip(li, range(len(li))))
print(d)

{'apple': 0, 'banana': 1, 'orange': 2}

Explanation: zip() pairs each element of the list li with an index from range(len(li)) and dict() converts these pairs into a dictionary, mapping each element to its corresponding index.

Using enumerate

enumerate() yields both the index and the value from an iterable. By using enumerate() within a loop or comprehension, we can easily pair each key with a unique integer its index . This is a simple and efficient way to assign distinct integer values to dictionary keys.

li = ['apple', 'banana', 'orange']
d = {} # initialized empty dictionary

for idx, key in enumerate(li):
    d[key] = idx
print(d)

{'apple': 0, 'banana': 1, 'orange': 2}

Explanation: enumerate() generates index-value pairs and the for loop adds each pair to the empty dictionary d, mapping each element to its index.

Using map()

map() applies a given function to each item of an iterable. By combining map() with range(), we can create a sequence of integers to map over the keys from a list. Though functional and elegant, this method introduces additional complexity and is slightly less efficient compared to the others.

li = ['apple', 'banana', 'orange']

d = dict(zip(li, map(lambda x: x, range(len(li)))))
print(d)

{'apple': 0, 'banana': 1, 'orange': 2}

Explanation: map() applies the identity function lambda x: x to each value in the range(len(li)), effectively creating a sequence of indices. The zip() function pairs each element of li with its corresponding index and dict() converts these pairs into a dictionary, mapping each element to its index.