How Can I Efficiently Convert a Tabular List to a Dictionary in Python?

Converting Tabular Lists to Dictionaries in Python

Often in programming, we encounter scenarios where data is organized in a tabular format, such as a list where even indices represent keys and odd indices represent corresponding values. The task is to transform this list into a dictionary.

Solution:

The cleanest and most efficient way to achieve this conversion is utilizing Python's built-in functions:

b = dict(zip(a[::2], a[1::2]))

This code effectively iterates over the list a, slicing it using the extended slice operator [::2], which skips every other element. The result is two lists: a[::2] contains the keys, and a[1::2] contains the values. These lists are then used to construct a dictionary using the dict() function.

For large lists, an alternative approach is recommended to avoid creating temporary lists:

from itertools import izip
i = iter(a)
b = dict(izip(i, i))

This method uses the iter() function to create an iterator for the list a. The izip() function (or zip() in Python 3) interleaves the elements from each iterator, creating a new iterator that yields tuples of keys and values. These tuples are then passed to dict() to construct the dictionary.

In Python 3, another syntactically convenient method is:

b = {a[i]: a[i+1] for i in range(0, len(a), 2)}

This code uses a dictionary comprehension that iterates over the list indices in steps of two, assembling keys and values into a new dictionary.

In Python 3.8 and later, the "walrus" operator (:=) provides a concise way to write this on a single line:

b = dict(zip(i := iter(a), i))

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