Walrus to the Rescue!
Using Python 3.8 Assignment Expressions :=
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Let’s say you have a publisher of messages, that sometimes sends an empty message:
You’d like to collect only the non-empty message from a list of publishers, so you try this:
The output is not what you expected:
Looking at the code, the reason becomes obvious: you call p.get() twice. The filter ( if p.get().strip()) is called first, and then the expression one on the left.
Looks like you’ll need to rewrite the code without list comprehension:
This prints out the expected result:
However, instead of a single line, you now have five to create and populate messages. Since there's a positive correlation between the number of lines of code and the number of bugs, less code is better (but not at the expense of readability).
What can you do? The walrus operator to the rescue! Python 3.8 added assignment expressions (known as the walrus operator since := looks a bit like a walrus emoticon), and they are really helpful in list comprehension.
Here’s the new code, which prints out the expected result.
The walrus operator is still fairly new (Python 3.8 came out in 2018) and the community is still figuring out the best ways to use it.
How do you use
:=?
If you like to solve programming problems, check out Miki Tebeka’s series of Brain Teaser books from The Pragmatic Bookshelf:
