How is a list comprehension created in Python?

A list comprehension in Python is created by enclosing an expression in square brackets, followed by a for loop. This concise syntax allows you to generate a new list by applying an expression to each item in an iterable, making your code more readable and efficient.

For example, if you want to create a list of squares for numbers from 1 to 5, you can use a list comprehension like this: [x**2 for x in range(1, 6)]. This single line of code effectively constructs a new list containing the squares of the numbers 1 through 5.

The other methods listed are not suitable for creating a list comprehension. Using curly braces is associated with creating a set or a dictionary, not a list. The list() function can be used to create a list from an iterable but does not allow you to apply an expression directly. Defining a function that returns a list requires more lines of code and does not utilize the concise syntax that a list comprehension provides. Thus, option B is the correct choice for defining a list comprehension in Python.