Python中arr = [-1]*n语句的含义与执行结果咨询

Hey there! Let me break down this Python syntax clearly—it’s a handy list creation trick that’s used all the time, so I’m glad you asked about it.

What the syntax means #

This is Python’s list multiplication feature. Here’s the simple breakdown:

• [-1] is a single-element list holding the integer -1
• The * operator, when paired with a list and an integer n, generates a new list by repeating the original list exactly n times

What arr contains after execution #

The resulting arr will be a list with n sequential copies of -1. For example:

• If n = 4, arr becomes [-1, -1, -1, -1]
• If n = 0 or n is a negative integer, arr will be an empty list []

A quick heads-up for edge cases #

This works flawlessly for immutable elements like integers, strings, or tuples. But if you try this with a mutable element (like another list, e.g., arr = [[]]*n), all the "copies" will reference the same underlying object—changing one will alter all of them! Since you’re using -1 here though, you don’t have to worry about that tricky gotcha.

内容的提问来源于stack exchange，提问作者RothX