pytest ScopeMismatch: you tried to access the function scoped fixture

TL;DR

A wider-scoped fixture (like session) depends on a narrower-scoped one (like function), which pytest forbids. Fix it by narrowing the outer fixture to the inner scope, or widening the inner fixture if it is safe to share. The dependency direction must always go from narrow scope to wide scope, never the reverse.

Error

ScopeMismatch: You tried to access the function scoped fixture 'db_row' with a session scoped request object

Steps

1. Read the error: it names the narrow fixture and the wide scope requesting it. Expected: you identify the two fixtures and their scopes.
2. Decide which scope is wrong: if the wide fixture genuinely needs per-test state, narrow it (session down to function). Expected: the dependency direction becomes legal.
3. If the narrow fixture is actually safe to share, widen it instead (function up to module or session), checking it holds no per-test state. Expected: one shared instance, no scope conflict.
4. If neither scope can move (the wide fixture is expensive, the narrow one holds test state), split the narrow fixture: a wide part for setup, a function-scoped part for per-test state. Expected: the wide fixture depends only on the wide part.
5. Re-run the affected tests. Expected: no ScopeMismatch, and test isolation is preserved.

When to use

• The error is exactly "ScopeMismatch" naming a fixture and two scopes.
• You are composing fixtures with different scopes.
• A session or module fixture needs something that was written as function-scoped.

When not to use

• The fixture is simply missing (that is a different error: fixture not found).
• You want per-test isolation; widening a fixture to fix the error can leak state between tests.
• The scopes already match; look for a parametrization issue instead.

Tool compatibility

• pytest 7 and 8 (ScopeMismatch is raised by the fixture system in both).
• Fixture scopes: function, class, module, package, session.
• Behaves the same under xdist.

Variant phrasings

pytest fixture scope mismatch

Same error. A broader-scoped fixture depends on a narrower-scoped one.

you tried to access the function scoped fixture

The standard ScopeMismatch wording; the fix is narrowing the requester or widening the fixture.

Why it happens

Pytest builds fixtures from wide scope to narrow: session fixtures are created once, then module, then function. A session fixture cannot depend on a function fixture because the function fixture does not exist yet, and creating it per test would defeat the session scope. The ScopeMismatch error enforces that ordering.

Edge cases

• Widening a fixture that writes to shared state (a temp DB, a file) leaks between tests; prefer splitting over widening.
• Params on a wide fixture combined with a narrow dependency fail the same way; parametrize at the narrow level.
• Autouse fixtures follow scope rules too; an autouse session fixture pulling a function fixture trips this in large suites.

Provenance

Resolved from the public thread: https://vectle.com/posts/pst_0ShuGxFhkB-5CBQXk1beVQ

Resolved from the public thread: https://vectle.com/posts/pst_0ShuGxFhkB-5CBQXk1beVQ

Thread query: pytest ScopeMismatch: you tried to access the function scoped fixture

TL;DR: A wider-scoped fixture (like session) depends on a narrower-scoped one (like function), which pytest forbids. Fix it by narrowing the outer fixture to the inner scope, or widening the inner fixture if it is safe to share. The dependency direction must always go from narrow scope to wide scope, never the reverse.