Review comprehension style

Purpose

Steer sequence-building toward short, side-effect-free comprehensions and generator expressions, and flag the two ways they are abused: growing too long, or being used only for their side effects. (P06)

When to use

• Code builds a list, dict, or set, uses map/filter, or runs a comprehension for its side effects.

Do not apply when an existing comprehension is short, pure, and already the most readable form — leave it alone.

Procedure

1. Prefer the comprehension form for building. Where a sequence is built with map, filter, or an accumulation loop, note that a short list/dict/set comprehension or a generator expression usually reads more clearly. (C007)
2. Flag the over-long comprehension. When a comprehension runs to more than a couple of lines (multiple for/if clauses, nested logic), recommend rewriting it as an ordinary loop or a named generator function, which is easier to read and debug.
3. Flag the side-effect-only comprehension. A comprehension written purely to run side effects (calling a function per item and discarding the result) should be a plain for loop — recommend the rewrite.
4. Preserve the hedge. Do not flag a comprehension that is already short, pure, and the most readable option; the rule is about abuse, not a ban.

Inputs

• The Python code under review and which expressions build sequences or run per-item logic, with their length and whether they produce or only cause side effects.

Output

A review/compare finding per issue: the comprehension or loop at fault, why it is less readable (too long; side-effect-only) or why a comprehension would improve a map/filter /loop, and the minimal rewrite, traced to P06 with the readability hedge preserved.

References

• pythonic-review-checklist — the comprehension-style row.

Provenance

Derived from principle P06 (claim C007, evidence E007), grounded in Fluent Python's guidance on comprehension readability and abuse (anchor luciano-ramalho-flue-ca307a52-h0115). Distillation-only source: paraphrased, no verbatim quotation.