Is chained method (method cascading) encouraged or discouraged by pep?

Question

inspired by this post, I am assuming that PEP8 is discouraging chained method (method cascading).

built-ins are the proof.

>>> x = list()
>>> x.append(1).append(2)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: 'NoneType' object has no attribute 'append'

but i didn't find related doc by search on pep

any idea?

This won't work anyway because `append` doesn't return anything. It just modifies the list in-place — Nenri, Apr 01 '19 at 10:04
(and the only list method i'm aware of that can be chained is `.copy()` but it doesn't even chain on the original list but a copy of it) — Nenri, Apr 01 '19 at 10:05
The post you linked to doesn't say what you claim. It doesn't even mention PEP. — khelwood, Apr 01 '19 at 10:08

score 1 · Accepted Answer · answered Apr 01 '19 at 10:52

PEP 8 leaves serval things up to you to decide how best to layout your code. The key theme throughout is that your code should be clear and readable. The example you provide doesn’t work as .append returns nothing.

Here is an example with strings:

x = "This"
x = x.strip().replace("T","t")
print (x)

Which might be easier to read in the following layout:

x = "This"
x = (x
     .strip()
     .replace("T","t")
     )
print (x)

Is chained method (method cascading) encouraged or discouraged by pep?

1 Answers1