Example 1

Never write:

[[0] * 5] * 10

this clause you can only use once, [0] * 5, like this.

But if you use [[0] * 5] * 10 instead of [[0]*5 for _ in range(10)], that will make your variable sharing to others.

Example 2

Never write:

def append_to(element, to=[]):
    to.append(element)
    return to

Instead, you should write:

def append_to(element, to=None):
    if to is None:
        to = []
    to.append(element)
    return to

This example come from, (https://docs.python-guide.org/writing/gotchas/#mutable-default-arguments)

I met this problem at: 208. Implement Trie (Prefix Tree) from leetcode, and my code clip is,

class TNode:
    def __init__(self, childs = {}):
        self.childs = childs
        self.isEnd = False

I don’t know where the element can come from an empty dictionary, that’s really crazy. Then I check comments.

Create a new object each time the function is called, by using a default arg to signal that no argument was provided (None is often a good choice).