Why Does Python Treat `('a')` as a String, Not a Tuple?

The Enigma of Singleton Tuples and their Stringy Conversion

When creating a tuple with a single element, you might expect it to retain its tuple nature. However, in Python, a peculiar behavior occurs.

The Problem:

Consider the following code:

a = [('a'), ('b'), ('c', 'd')]

Surprisingly, when you print the type of each element in a, you get the following output:

['a', 'b', ('c', 'd')]
<type 'str'>
<type 'str'>
<type 'tuple'>

Why do the first two elements, despite being enclosed in parentheses, behave as strings instead of tuples?

The Answer:

The key lies in understanding the Python syntax for tuples. Parentheses alone do not create a tuple with a single element. To do so, you must add a comma after the element. This distinction is illustrated below:

type(('a'))  # A string
type(('a',))  # A tuple

To correct the code example, add commas after the single-element strings:

a = [('a',), ('b',), ('c', 'd')]

The Reason:

According to the Python documentation, empty tuples and tuples with a single item have unique syntax requirements. Empty tuples are created with an empty pair of parentheses, while tuples with a single item require a value followed by a comma.

A Circumvention:

If you find the trailing comma to be aesthetically displeasing, you can create a tuple with a single element by passing a list to the tuple() function:

x = tuple(['a'])

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