Why Does Python\'s `list.append()` Return False in a Boolean Context?

Evaluating Boolean Contexts in Python: Why list.append() Returns False

Python boasts a unique approach to evaluating objects in boolean contexts. When faced with a container, such as a list, it evaluates its truthiness based on whether it contains elements. Hence, an empty list is inherently False, while a non-empty list is True.

However, the list.append() method presents an interesting conundrum. Its primary purpose is to modify the list by appending an element. Surprisingly, in a boolean context, list.append() evaluates to False.

Unveiling the Rationale

The fundamental reason for this behavior lies in Python's adherence to the Command-query separation principle. This principle dictates that methods that modify data structures should not return a meaningful value. Consequently, most mutating methods in Python, including list.append(), return None.

Exceptions to the Rule

While the norm is for mutators to return None, there are occasional exceptions. For instance, pop, which removes an element from a list, returns the removed value. Such exceptions are introduced to avoid costly or cluttered code in situations where recovering the changed value is critical.

Applying the Principle to list.append()

Applying this principle to list.append(), it becomes evident that there is no practical reason to deviate from the convention of returning None. After all, the modified list itself is available directly to the programmer. Returning a boolean value would only introduce ambiguity, making the code less straightforward to understand.

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