feat: add provider.derive(fn) to inject a value computed from another provider by lesnik512 · Pull Request #733 · modern-python/modern-di

lesnik512 · 2026-10-19T06:17:19Z

Closes #730.

Adds provider.derive(fn), a provider of fn(value), where value is what provider resolves to. It covers the settings case from discussion #136:

class Dependencies(Group):
    settings = providers.Factory(Settings, cache=True)
    database = providers.Factory(
        Database,
        kwargs={"dsn": settings.derive(lambda s: s.db_dsn)},
        cache=True,
    )

mypy, pyright and ty all infer s from settings and flag s.db_dns. A derived provider is never cached, has no scope of its own and is not registered under any type. Overriding the source reaches it, and so does overriding the derived provider directly. validate() checks the consuming factory against the source's effective scope and never calls fn. An exception from fn is re-raised unchanged with a note: raised by the function of Settings.derive (module:line).

Design notes:

The class _Derived is private and lives in providers/abstract.py, not providers/derived.py as the issue said. AbstractProvider.derive builds it, so a separate module would need a circular import.
dependency_graph.scope_chain extends terminal_chain through derived sources. effective_scope and the scope checks in collect_errors use it. redirect_target is unchanged, because a derived node is a step of its own in the chain, not a hop.
The resolver is a closure: fn(source_resolver(container)). That costs two Python calls per node, the same as a Factory, and test_derived_node_costs_its_resolver_frame_and_fn pins it.
AbstractProvider.__init__ takes call_depth so the call site recorded for a derived provider is the user's derive(...) line.
The note names only the derived step, not the whole chain from the root, the same way finalizer_note does.
There is no separate recipe page. The "Derived values" section in docs/providers/factories.md carries the settings example. The AttrGetter and .provided rows in the migration guides now point there.

#732, which gives inline providers the group's scope, is a separate branch. Whichever lands second needs a small rebase. #732's inline-scope walk will also need a branch for derived sources.

This was generated by AI.

… provider settings.derive(lambda s: s.db_dsn) is a provider of fn(value). Type checkers infer s from the source. It is never cached, has no scope of its own and resolves at its source's effective scope, so it works inline in kwargs in any group and an override of the source reaches it. An exception raised by fn propagates unchanged, with a note naming the derived provider. The class is private (_Derived) and lives in providers/abstract.py, because the derive method on AbstractProvider needs it, and a separate module would create an import cycle. Closes #730

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Benchmark

Details

Benchmark suite	Current: `16b7f7e`	Previous: `5644031`	Ratio
`benchmarks/test_guard_by_type.py::test_g16_resolve_by_type`	`5688748.111334327` iter/sec (`stddev: 1.835784278806345e-8`)	`4904470.719322522` iter/sec (`stddev: 8.90402796485949e-9`)	`0.86`
`benchmarks/test_guard_by_type.py::test_g17_resolve_by_type_large_registry`	`5859863.817923041` iter/sec (`stddev: 1.6118092909924765e-8`)	`4840463.4085030025` iter/sec (`stddev: 1.2665696484187963e-8`)	`0.83`
`benchmarks/test_guard_cold.py::test_g8_cold_first_resolve`	`19816.274017584732` iter/sec (`stddev: 0.00004034859102604059`)	`23628.313618776076` iter/sec (`stddev: 0.00003977866103226871`)	`1.19`
`benchmarks/test_guard_cold.py::test_g8b_cold_first_resolve_cached`	`15553.078006793326` iter/sec (`stddev: 0.00013864966221817962`)	`18648.76958371226` iter/sec (`stddev: 0.00013151010005662552`)	`1.20`
`benchmarks/test_guard_concurrency.py::test_g14_concurrent_cached_hit[1]`	`777.851822658794` iter/sec (`stddev: 0.000040883666344383664`)	`635.49521612325` iter/sec (`stddev: 0.00010830725124873891`)	`0.82`
`benchmarks/test_guard_concurrency.py::test_g14_concurrent_cached_hit[2]`	`732.7812404570436` iter/sec (`stddev: 0.000056866581075568786`)	`622.2577111713392` iter/sec (`stddev: 0.000022994150438437634`)	`0.85`
`benchmarks/test_guard_concurrency.py::test_g14_concurrent_cached_hit[4]`	`688.3813254253176` iter/sec (`stddev: 0.000055503270910848876`)	`600.8444213149718` iter/sec (`stddev: 0.00003111836380343128`)	`0.87`
`benchmarks/test_guard_concurrency.py::test_g15_concurrent_first_resolve[1]`	`16173.409136434311` iter/sec (`stddev: 0.000011900032408579106`)	`19253.65454423782` iter/sec (`stddev: 0.000006325155207578131`)	`1.19`
`benchmarks/test_guard_concurrency.py::test_g15_concurrent_first_resolve[2]`	`6346.400837090051` iter/sec (`stddev: 0.00003463308509007541`)	`9804.191504426777` iter/sec (`stddev: 0.000018586115607355884`)	`1.54`
`benchmarks/test_guard_concurrency.py::test_g15_concurrent_first_resolve[4]`	`3415.8624682695195` iter/sec (`stddev: 0.00004535892669506383`)	`5039.582349677059` iter/sec (`stddev: 0.00002463455424331871`)	`1.48`
`benchmarks/test_guard_concurrency.py::test_g15b_concurrent_first_resolve_sibling_children[1]`	`12530.022455842092` iter/sec (`stddev: 0.000010984717487878114`)	`14602.474998002726` iter/sec (`stddev: 0.000027412516970430302`)	`1.17`
`benchmarks/test_guard_concurrency.py::test_g15b_concurrent_first_resolve_sibling_children[2]`	`4786.674281731906` iter/sec (`stddev: 0.00002930509145646027`)	`6404.044965525755` iter/sec (`stddev: 0.000015517061243459845`)	`1.34`
`benchmarks/test_guard_concurrency.py::test_g15b_concurrent_first_resolve_sibling_children[4]`	`2248.961668454162` iter/sec (`stddev: 0.00005240594445521762`)	`3011.8917014085687` iter/sec (`stddev: 0.000026324174080671828`)	`1.34`
`benchmarks/test_guard_concurrency.py::test_g15c_worker_pool_floor_control[1]`	`31252.70205603029` iter/sec (`stddev: 0.000006610706983284418`)	`53793.88067732621` iter/sec (`stddev: 0.0000022875613335364985`)	`1.72`
`benchmarks/test_guard_concurrency.py::test_g15c_worker_pool_floor_control[2]`	`11985.558600412329` iter/sec (`stddev: 0.000024845369830575134`)	`23331.437654305966` iter/sec (`stddev: 0.000006265710218518168`)	`1.95`
`benchmarks/test_guard_concurrency.py::test_g15c_worker_pool_floor_control[4]`	`5438.430642952551` iter/sec (`stddev: 0.00004095086582800911`)	`8590.035201249366` iter/sec (`stddev: 0.000022493863850767943`)	`1.58`
`benchmarks/test_guard_lifecycle.py::test_g6_build_child_container`	`2250176.9201494516` iter/sec (`stddev: 3.615768058648405e-8`)	`2113855.7590402174` iter/sec (`stddev: 2.031861697710027e-8`)	`0.94`
`benchmarks/test_guard_lifecycle.py::test_g6b_build_child_container_auto_scope`	`2461037.924291189` iter/sec (`stddev: 3.886570985644965e-8`)	`2349543.3221972664` iter/sec (`stddev: 1.6650926537950493e-8`)	`0.95`
`benchmarks/test_guard_lifecycle.py::test_g7_request_lifecycle_batch`	`4180.551436665803` iter/sec (`stddev: 0.000007008447618006861`)	`4451.999269637383` iter/sec (`stddev: 0.000019825297086034126`)	`1.06`
`benchmarks/test_guard_lifecycle.py::test_g7c_event_loop_floor_control`	`81831.96167710234` iter/sec (`stddev: 0.0000011438983832709063`)	`75792.7049367867` iter/sec (`stddev: 0.0000010181345487109347`)	`0.93`
`benchmarks/test_guard_lifecycle.py::test_g7b_request_cycle_sync`	`578864.4323811524` iter/sec (`stddev: 6.561305324599335e-8`)	`579072.6614580763` iter/sec (`stddev: 7.801953521917385e-8`)	`1.00`
`benchmarks/test_guard_lifecycle.py::test_g13_teardown_at_scale`	`84016.68440863906` iter/sec (`stddev: 0.0000013029683975836587`)	`89586.42894679612` iter/sec (`stddev: 9.419924223584152e-7`)	`1.07`
`benchmarks/test_guard_lifecycle.py::test_g13b_teardown_at_scale_async_no_finalizers`	`767.6633772670398` iter/sec (`stddev: 0.0012014510800948679`)	`808.4589055286162` iter/sec (`stddev: 0.0010166585713580374`)	`1.05`
`benchmarks/test_guard_resolve.py::test_g1_transient_resolve`	`3274826.376899151` iter/sec (`stddev: 2.751959581092676e-8`)	`2993114.7137404513` iter/sec (`stddev: 2.3521816194443065e-8`)	`0.91`
`benchmarks/test_guard_resolve.py::test_g2_cached_resolve`	`5476376.281836439` iter/sec (`stddev: 1.363982460503147e-8`)	`4816101.962687137` iter/sec (`stddev: 5.295105482873398e-9`)	`0.88`
`benchmarks/test_guard_resolve.py::test_g3_deep_chain`	`1207090.2793101487` iter/sec (`stddev: 4.1405091565502474e-8`)	`1113569.6873886315` iter/sec (`stddev: 3.487097985959811e-8`)	`0.92`
`benchmarks/test_guard_resolve.py::test_g4_wide_resolve`	`681966.4242686173` iter/sec (`stddev: 3.612952682357208e-7`)	`612604.315410136` iter/sec (`stddev: 3.4851084483792727e-7`)	`0.90`
`benchmarks/test_guard_resolve.py::test_g5_cross_scope`	`2825883.139694212` iter/sec (`stddev: 2.3994413132611186e-8`)	`2674624.3874501064` iter/sec (`stddev: 2.4053681698733978e-8`)	`0.95`
`benchmarks/test_guard_resolve.py::test_g9_context_resolve`	`2142767.452735959` iter/sec (`stddev: 1.269114249373723e-7`)	`1960294.8165720731` iter/sec (`stddev: 1.311245293630255e-7`)	`0.91`
`benchmarks/test_guard_resolve.py::test_g12_override_active_resolve`	`1223976.2754155502` iter/sec (`stddev: 3.7142038160007894e-8`)	`1180518.9348746464` iter/sec (`stddev: 5.260935842068453e-8`)	`0.96`
`benchmarks/test_guard_resolve.py::test_g18_alias_hop`	`5697638.516862223` iter/sec (`stddev: 1.396202929205016e-8`)	`4813390.158237099` iter/sec (`stddev: 4.760819374662499e-9`)	`0.84`
`benchmarks/test_guard_validate.py::test_g10_validate_deep_chain`	`42333.4150131789` iter/sec (`stddev: 0.000015519171916960328`)	`53266.10819056237` iter/sec (`stddev: 0.000014901713787393878`)	`1.26`
`benchmarks/test_guard_validate.py::test_g11_validate_wide`	`25905.449874576603` iter/sec (`stddev: 0.00002038012677720931`)	`31125.67788213068` iter/sec (`stddev: 0.000019062727395208582`)	`1.20`

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lesnik512 added the enhancement New feature or request label Oct 19, 2026

github-actions Bot reviewed Oct 19, 2026

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lesnik512 merged commit 839b719 into main Oct 19, 2026
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lesnik512 deleted the feat/provider-derive branch October 19, 2026 06:22

lesnik512 mentioned this pull request Oct 19, 2026

fix: give inline providers in Factory kwargs the scope of the providers using them #734

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feat: add provider.derive(fn) to inject a value computed from another provider - #733

feat: add provider.derive(fn) to inject a value computed from another provider#733
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feat/provider-derive

lesnik512 commented Oct 19, 2026

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