You can whitewash this away by discussing order of evaluation, but it still is a great example of how Python continually mixes up concepts of expressions and statements and immutable and mutable data. In real life, if I ask someone to go get me four empty buckets, I expect them to come back with four
distinct empty buckets. The intuitive interpretation of [[]]*4 is asking just that. Instead Python creates
a bucket and then gives you a piece of paper that lists its address four times. Why does one want that,
by default?
In more sane languages, the expression [] means give me an empty list value, nothing more and nothing less. So then whatever the syntax for [[]]*4 is in such sane languages, it gives you four empty list values. If you want something more imperative, you can get it, but it most cases, you don't want or even need such things.
Python makes no distinction, at a level able to be visualized by the user, between immutable and mutable data. There are a lot of bizarre situations in Python that will bite you like this. And in most cases, it's strange that such behaviors were chosen as the deault.
In more sane languages, the expression [] means give me an empty list value, nothing more and nothing less. So then whatever the syntax for [[]]*4 is in such sane languages, it gives you four empty list values. If you want something more imperative, you can get it, but it most cases, you don't want or even need such things.
Python makes no distinction, at a level able to be visualized by the user, between immutable and mutable data. There are a lot of bizarre situations in Python that will bite you like this. And in most cases, it's strange that such behaviors were chosen as the deault.