Function _navigation

lib/streamlit/commands/navigation.py:332–494

(
    pages: Sequence[PageType] | Mapping[SectionHeader, Sequence[PageType]],
    *,
    position: Literal["sidebar", "hidden", "top"],
    expanded: bool | int,
)

def _navigation(
    pages: Sequence[PageType] | Mapping[SectionHeader, Sequence[PageType]],
    *,
    position: Literal["sidebar", "hidden", "top"],
    expanded: bool | int,
) -> StreamlitPage:
    if isinstance(pages, Sequence):
        converted_pages = [convert_to_streamlit_page(p) for p in pages]
        nav_sections = {"": converted_pages}
    else:
        nav_sections = {
            section: [convert_to_streamlit_page(p) for p in section_pages]
            for section, section_pages in pages.items()
        }
    page_list = pages_from_nav_sections(nav_sections)

    if not page_list:
        raise StreamlitAPIException(
            "`st.navigation` must be called with at least one `st.Page`."
        )

    default_page = None
    pagehash_to_pageinfo: dict[PageHash, PageInfo] = {}

    # Get the default page.
    for section_header in nav_sections:
        for page in nav_sections[section_header]:
            if page._default:
                if default_page is not None:
                    raise StreamlitAPIException(
                        "Multiple Pages specified with `default=True`. "
                        "At most one Page can be set to default."
                    )
                default_page = page

    if default_page is None:
        non_external_pages = [p for p in page_list if not p.is_external]
        if not non_external_pages:
            raise StreamlitAPIException(
                "At least one non-external page is required. "
                "External URL pages cannot be the default page."
            )
        default_page = non_external_pages[0]
        default_page._default = True

    ctx = get_script_run_ctx()
    if not ctx:
        # This should never run in Streamlit, but we want to make sure that
        # the function always returns a page
        default_page._can_be_called = True
        return default_page

    # Build the pagehash-to-pageinfo mapping.
    for section_header in nav_sections:
        for page in nav_sections[section_header]:
            script_path = str(page._page) if isinstance(page._page, Path) else ""

            script_hash = page._script_hash