Beware of the pit of the repeating operator (*) in Python

In fact, there are a lot of people on the Internet that have been mentioned, but did not pay attention to this matter until recently, they have been a hole.

Python does not seem to directly define a sequence of specified lengths (tuple, list, etc.), but you can repeat the operator multiplication sign to construct a sequence to achieve the specified length:

Seq = [{}] * 10

This builds a list of dictionaries with an initial length of 10. But this line of human and animal harmless code is hidden in crisis, because the list of 10 dictionary references in fact point to the same dictionary instance! An equivalent notation might seem clearer:

TMP = {}SEQ = [tmp] * 10

It is estimated that most of the cases this is not the expected effect of the person writing the previous line of code.

Remember, be alert!

Beware of the pit of the repeating operator (*) in Python