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Citations

CitationExplorer traverses the citation graph around a paper: the papers that cite it, the papers it references, and the canonical (most-cited) papers in a field. It is an async context manager and returns CitationResult objects.

from opencite import Config
from opencite.citations import CitationExplorer

async with CitationExplorer(Config.from_env()) as explorer:
    citing = await explorer.citing_papers("10.1038/nature12345", max_results=20)
    refs = await explorer.references("10.1038/nature12345")
    landmarks = await explorer.canonical_papers("deep learning", min_citations=5000)

CitationExplorer

Explores citation graphs and finds canonical papers.

Honors config.disabled_sources: a disabled source's client is never constructed, so its rate budget isn't touched and its async failures can't slow down the parallel gather. Disabling both openalex and s2 leaves nothing to query and raises at construction time.

Usage::

async with CitationExplorer(config) as explorer:
    result = await explorer.citing_papers("10.1038/s41586-021-03819-2")
    for paper in result.papers:
        print(paper.title)
Source code in src/opencite/citations.py 
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class CitationExplorer:
    """Explores citation graphs and finds canonical papers.

    Honors `config.disabled_sources`: a disabled source's client is never
    constructed, so its rate budget isn't touched and its async failures
    can't slow down the parallel gather. Disabling both `openalex` and
    `s2` leaves nothing to query and raises at construction time.

    Usage::

        async with CitationExplorer(config) as explorer:
            result = await explorer.citing_papers("10.1038/s41586-021-03819-2")
            for paper in result.papers:
                print(paper.title)
    """

    def __init__(self, config: Config):
        self.config = config
        self._openalex: OpenAlexClient | None = (
            OpenAlexClient(config)
            if is_source_enabled("openalex", config.disabled_sources)
            else None
        )
        self._s2: SemanticScholarClient | None = (
            SemanticScholarClient(config)
            if is_source_enabled("s2", config.disabled_sources)
            else None
        )
        if self._openalex is None and self._s2 is None:
            raise ValueError(
                "CitationExplorer needs at least one of `openalex` or `s2`; "
                "both are listed in config.disabled_sources."
            )

    async def __aenter__(self) -> CitationExplorer:
        if self._openalex is not None:
            await self._openalex.__aenter__()
        if self._s2 is not None:
            await self._s2.__aenter__()
        return self

    async def __aexit__(self, *args: object) -> None:
        if self._openalex is not None:
            await self._openalex.__aexit__()
        if self._s2 is not None:
            await self._s2.__aexit__()

    async def citing_papers(
        self,
        identifier: str,
        max_results: int = 50,
        sort: str = "citations",
        min_citations: int = 0,
    ) -> CitationResult:
        """Find papers that cite the given paper."""
        id_type, id_value = parse_identifier(identifier)

        # Get the seed paper first
        seed = await self._lookup_seed(id_type, id_value)
        if seed is None:
            return CitationResult(
                seed_paper=Paper(title="Unknown", ids=_make_ids(id_type, id_value)),
                papers=[],
                direction="citing",
            )

        # Get citing papers from available sources
        tasks: list[asyncio.Task[list[Paper]]] = []

        if self._openalex is not None and seed.ids.openalex_id:
            tasks.append(
                asyncio.create_task(
                    self._openalex.citing_papers(
                        seed.ids.openalex_id, max_results=max_results, sort=sort
                    )
                )
            )
        if self._s2 is not None:
            if seed.ids.s2_id:
                tasks.append(
                    asyncio.create_task(
                        self._s2.citing_papers(
                            seed.ids.s2_id, max_results=max_results
                        )
                    )
                )
            elif seed.doi:
                tasks.append(
                    asyncio.create_task(
                        self._s2.citing_papers(
                            f"DOI:{seed.doi}", max_results=max_results
                        )
                    )
                )

        all_papers = await _gather_papers(tasks)

        # Deduplicate and filter
        unique = deduplicate(all_papers)
        if min_citations > 0:
            unique = [p for p in unique if p.citation_count >= min_citations]

        # Sort
        unique = _sort_papers(unique, sort)
        unique = unique[:max_results]

        return CitationResult(
            seed_paper=seed,
            papers=unique,
            direction="citing",
            total_available=len(all_papers),
        )

    async def references(
        self,
        identifier: str,
        max_results: int = 50,
    ) -> CitationResult:
        """Find papers referenced by the given paper."""
        id_type, id_value = parse_identifier(identifier)
        seed = await self._lookup_seed(id_type, id_value)
        if seed is None:
            return CitationResult(
                seed_paper=Paper(title="Unknown", ids=_make_ids(id_type, id_value)),
                papers=[],
                direction="references",
            )

        tasks: list[asyncio.Task[list[Paper]]] = []

        if self._openalex is not None and seed.ids.openalex_id:
            tasks.append(
                asyncio.create_task(
                    self._openalex.references(
                        seed.ids.openalex_id, max_results=max_results
                    )
                )
            )
        if self._s2 is not None:
            if seed.ids.s2_id:
                tasks.append(
                    asyncio.create_task(
                        self._s2.references(seed.ids.s2_id, max_results=max_results)
                    )
                )
            elif seed.doi:
                tasks.append(
                    asyncio.create_task(
                        self._s2.references(
                            f"DOI:{seed.doi}", max_results=max_results
                        )
                    )
                )

        all_papers = await _gather_papers(tasks)
        unique = deduplicate(all_papers)
        unique = unique[:max_results]

        return CitationResult(
            seed_paper=seed,
            papers=unique,
            direction="references",
            total_available=len(all_papers),
        )

    async def canonical_papers(
        self,
        query: str,
        max_results: int = 10,
        year_from: int | None = None,
        min_citations: int = 100,
    ) -> list[Paper]:
        """Find the most-cited papers in a field.

        Uses OpenAlex sorted by citation count descending. Raises
        `RuntimeError` if `openalex` is disabled, since no other source
        in the explorer can substitute.
        """
        if self._openalex is None:
            raise RuntimeError(
                "canonical_papers requires `openalex`, which is disabled in "
                "config.disabled_sources."
            )
        papers = await self._openalex.canonical_search(
            query,
            max_results=max_results,
            year_from=year_from,
            min_citations=min_citations,
        )
        return papers

    async def _lookup_seed(self, id_type: IDType, id_value: str) -> Paper | None:
        """Look up the seed paper to get IDs for citation queries.

        When a source is disabled, fall back to whichever client is still
        constructed; if neither can serve the ID type, return None.
        """
        from opencite.dedup import merge_papers

        s2_lookup = self._s2.lookup if self._s2 is not None else None
        openalex_doi = self._openalex.lookup_doi if self._openalex is not None else None

        if id_type == IDType.DOI:
            paper = await s2_lookup(f"DOI:{id_value}") if s2_lookup else None
            if paper:
                if openalex_doi:
                    oa_paper = await openalex_doi(id_value)
                    if oa_paper:
                        paper = merge_papers(paper, oa_paper)
                return paper
            return await openalex_doi(id_value) if openalex_doi else None

        if id_type == IDType.PMID:
            paper = await s2_lookup(f"PMID:{id_value}") if s2_lookup else None
            if paper and paper.doi and openalex_doi:
                oa_paper = await openalex_doi(paper.doi)
                if oa_paper:
                    paper = merge_papers(paper, oa_paper)
            return paper

        if id_type == IDType.ARXIV:
            return await s2_lookup(f"ARXIV:{id_value}") if s2_lookup else None

        if id_type == IDType.S2:
            return await s2_lookup(id_value) if s2_lookup else None

        if id_type == IDType.OPENALEX:
            return await openalex_doi(id_value) if openalex_doi else None

        return None

citing_papers async 

citing_papers(
    identifier: str,
    max_results: int = 50,
    sort: str = "citations",
    min_citations: int = 0,
) -> CitationResult

Find papers that cite the given paper.

Source code in src/opencite/citations.py 
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async def citing_papers(
    self,
    identifier: str,
    max_results: int = 50,
    sort: str = "citations",
    min_citations: int = 0,
) -> CitationResult:
    """Find papers that cite the given paper."""
    id_type, id_value = parse_identifier(identifier)

    # Get the seed paper first
    seed = await self._lookup_seed(id_type, id_value)
    if seed is None:
        return CitationResult(
            seed_paper=Paper(title="Unknown", ids=_make_ids(id_type, id_value)),
            papers=[],
            direction="citing",
        )

    # Get citing papers from available sources
    tasks: list[asyncio.Task[list[Paper]]] = []

    if self._openalex is not None and seed.ids.openalex_id:
        tasks.append(
            asyncio.create_task(
                self._openalex.citing_papers(
                    seed.ids.openalex_id, max_results=max_results, sort=sort
                )
            )
        )
    if self._s2 is not None:
        if seed.ids.s2_id:
            tasks.append(
                asyncio.create_task(
                    self._s2.citing_papers(
                        seed.ids.s2_id, max_results=max_results
                    )
                )
            )
        elif seed.doi:
            tasks.append(
                asyncio.create_task(
                    self._s2.citing_papers(
                        f"DOI:{seed.doi}", max_results=max_results
                    )
                )
            )

    all_papers = await _gather_papers(tasks)

    # Deduplicate and filter
    unique = deduplicate(all_papers)
    if min_citations > 0:
        unique = [p for p in unique if p.citation_count >= min_citations]

    # Sort
    unique = _sort_papers(unique, sort)
    unique = unique[:max_results]

    return CitationResult(
        seed_paper=seed,
        papers=unique,
        direction="citing",
        total_available=len(all_papers),
    )

references async 

references(
    identifier: str, max_results: int = 50
) -> CitationResult

Find papers referenced by the given paper.

Source code in src/opencite/citations.py 
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async def references(
    self,
    identifier: str,
    max_results: int = 50,
) -> CitationResult:
    """Find papers referenced by the given paper."""
    id_type, id_value = parse_identifier(identifier)
    seed = await self._lookup_seed(id_type, id_value)
    if seed is None:
        return CitationResult(
            seed_paper=Paper(title="Unknown", ids=_make_ids(id_type, id_value)),
            papers=[],
            direction="references",
        )

    tasks: list[asyncio.Task[list[Paper]]] = []

    if self._openalex is not None and seed.ids.openalex_id:
        tasks.append(
            asyncio.create_task(
                self._openalex.references(
                    seed.ids.openalex_id, max_results=max_results
                )
            )
        )
    if self._s2 is not None:
        if seed.ids.s2_id:
            tasks.append(
                asyncio.create_task(
                    self._s2.references(seed.ids.s2_id, max_results=max_results)
                )
            )
        elif seed.doi:
            tasks.append(
                asyncio.create_task(
                    self._s2.references(
                        f"DOI:{seed.doi}", max_results=max_results
                    )
                )
            )

    all_papers = await _gather_papers(tasks)
    unique = deduplicate(all_papers)
    unique = unique[:max_results]

    return CitationResult(
        seed_paper=seed,
        papers=unique,
        direction="references",
        total_available=len(all_papers),
    )

canonical_papers async 

canonical_papers(
    query: str,
    max_results: int = 10,
    year_from: int | None = None,
    min_citations: int = 100,
) -> list[Paper]

Find the most-cited papers in a field.

Uses OpenAlex sorted by citation count descending. Raises RuntimeError if openalex is disabled, since no other source in the explorer can substitute.

Source code in src/opencite/citations.py 
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async def canonical_papers(
    self,
    query: str,
    max_results: int = 10,
    year_from: int | None = None,
    min_citations: int = 100,
) -> list[Paper]:
    """Find the most-cited papers in a field.

    Uses OpenAlex sorted by citation count descending. Raises
    `RuntimeError` if `openalex` is disabled, since no other source
    in the explorer can substitute.
    """
    if self._openalex is None:
        raise RuntimeError(
            "canonical_papers requires `openalex`, which is disabled in "
            "config.disabled_sources."
        )
    papers = await self._openalex.canonical_search(
        query,
        max_results=max_results,
        year_from=year_from,
        min_citations=min_citations,
    )
    return papers