gh-137818: Add multiple if statements example for list comprehensions

[Hello-world150]

• Issue: Document usage of comprehensions with multiple if clauses #137818

---

📚 Documentation preview 📚: https://cpython-previews--138217.org.readthedocs.build/

[sergey-miryanov]

It looks valid for me.

[efimov-mikhail]

Suggested change

	Note the second :keyword:`!if` is replaced by :keyword:`!and`.
	Note that the second :keyword:`!if` has been replaced with :keyword:`!and`.

[terryjreedy]

Adding 'that' would be correct if we add the note and patch, but I am considering whether to do so.

[pochmann3]

Looks redundant/misleading to me. As I said in the issue, the conditions are not and-ed, the clauses are nested and the documentation already says and shows that.

[pochmann3]

Those aren't if statements but if clauses.

[pochmann3]

Looks redundant/misleading to me.

For example for a case of four clauses for-if-for-if, I can imagine the "and explanation" to confuse learners into thinking that those two ifs get and-ed somehow. Whereas thinking correctly about it, with nested statements as already documented, there's no issue.

[serhiy-storchaka]

I do not think this is needed. This is trivial, and it is the same as for nested ifs. There is no reason to use two consequent if clauses, you can simply use and. No need to document an anti-pattern.

[efimov-mikhail]

No need to document an anti-pattern.

Framing this way I tend to change my mind. It'll be better to close this PR.

Thanks to everyone for the reviews! It was also very helpful for my understanding. I will revoke my approval.

There's no need in this change at all

[pochmann3]

There is no reason to use two consequent if clauses

Not quite true, I have a reason and sometimes do that. When I split a "long" condition into multiple physical lines, I prefer one clause per line and having sub-conditions aligned vertically:

lst = [
    ...
    for x in ...
    if longCondition
    if anotherLongCondition
]

I wouldn't like an and there.

[serhiy-storchaka]

Well, there may be stylistic reason. But it is not applicable for simple conditions like in the proposed example, and discussing stylistic nuances is out of scope of the language reference.

[willingc]

Thanks for the submission.

[willingc]

Suggested change

	A list comprehension consists of brackets containing an expression followed
	by a :keyword:`!for` clause, which may be followed by zero or more :keyword:`!for` or :keyword:`!if`
	clauses. The result will be a new list resulting from evaluating the expression
	in the context of the :keyword:`!for` and :keyword:`!if` clauses which follow it.
	For example, this listcomp combines the elements of two lists if they are not
	equal::

[willingc]

I would make this change as I think the current wording created the initial confusion in the issue.

[Hello-world150]

Thank you for your help. My English is not very good, please forgive me.

[hauntsaninja]

Thank you for your contribution! I agree with others that we don't need this example — more documentation is not always better documentation