Python syntax – using parentheses with indentation

Question

I’m taking a course on Polars and found the syntax I don’t fully understand.
Here’s sample from the course:

csvFile = "..\data\example.csv"
(
    pl.read_csv(csvFile)
    .filter(pl.col("Col").is_null())
)

this is working.
When I try to modify the line to

csvFile = "..\data\example.csv"
ex=(
    pl.read_csv(csvFile)
    .filter(pl.col("Col").is_null())
    
)

this is also working. But when I to make further changes to:

csvFile = "..\data\example.csv"
(
    ex=pl.read_csv(csvFile)
    .filter(pl.col("Col").is_null())
    
)

I get syntax error ex=pl.read_csv(csvFile)
^ SyntaxError: invalid syntax. Maybe you meant ‘==’ or ‘:=’ instead of ‘=’?

What is the meaning of these parentheses? I really like this kind of syntax but can’t find reference on how to use it properly. I’m using python 3.11 in VSCode with Jupyter extension.

Artur

Asked By: Artup

||

Source

Answer 1

A container enclosed by parenthesis is named a tuple. Tuples contain non-mutable order of items inside.

Tuple is similar to a List, where a Tuple is enclosed by () and a List is enclosed by [].

For example:

tuple_1 = (item1, item2, item3)
list_1 = [item1, item2, item3]

Answered By: Mijanur Rahman

Answer 2

That is just a way to put on several lines what should go on a single line. It’s just formatting stuff.

Both

(
    expression on 
    several lines
)

and

variable = (
    expression on
    several lines
)

works. In the first case your expression got evaluated but its output is not saved to any variable, in the second it does.

As a general rule, everything that is inside brackets (both round and squared ones) can be safely written on multiple lines for readability purposes, without needing to escape newline with a at the end of the lines. PEP8 contains all rules related to a good formatting of python code.

Answered By: mattiatantardini

Python syntax – using parentheses with indentation

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