{"id": "internals:internals-utils-parse-metadata", "page": "internals", "ref": "internals-utils-parse-metadata", "title": "parse_metadata(content)", "content": "This function accepts a string containing either JSON or YAML, expected to be of the format described in Metadata . It returns a nested Python dictionary representing the parsed data from that string. \n If the metadata cannot be parsed as either JSON or YAML the function will raise a utils.BadMetadataError exception. \n \n \n datasette.utils. parse_metadata content : str dict \n \n Detects if content is JSON or YAML and parses it appropriately.", "breadcrumbs": "[\"Internals for plugins\", \"The datasette.utils module\"]", "references": "[]"}
{"id": "internals:internals-utils-derive-named-parameters", "page": "internals", "ref": "internals-utils-derive-named-parameters", "title": "derive_named_parameters(db, sql)", "content": "Derive the list of named parameters referenced in a SQL query, using an explain query executed against the provided database. \n \n \n async datasette.utils. derive_named_parameters db : Database sql : str List [ str ] \n \n Given a SQL statement, return a list of named parameters that are used in the statement \n e.g. for select * from foo where id=:id this would return [\"id\"]", "breadcrumbs": "[\"Internals for plugins\", \"The datasette.utils module\"]", "references": "[]"}
{"id": "internals:internals-utils-await-me-maybe", "page": "internals", "ref": "internals-utils-await-me-maybe", "title": "await_me_maybe(value)", "content": "Utility function for calling await on a return value if it is awaitable, otherwise returning the value. This is used by Datasette to support plugin hooks that can optionally return awaitable functions. Read more about this function in The \u201cawait me maybe\u201d pattern for Python asyncio . \n \n \n async datasette.utils. await_me_maybe value : Any Any \n \n If value is callable, call it. If awaitable, await it. Otherwise return it.", "breadcrumbs": "[\"Internals for plugins\", \"The datasette.utils module\"]", "references": "[{\"href\": \"https://simonwillison.net/2020/Sep/2/await-me-maybe/\", \"label\": \"The \u201cawait me maybe\u201d pattern for Python asyncio\"}]"}
{"id": "internals:internals-utils", "page": "internals", "ref": "internals-utils", "title": "The datasette.utils module", "content": "The datasette.utils module contains various utility functions used by Datasette. As a general rule you should consider anything in this module to be unstable - functions and classes here could change without warning or be removed entirely between Datasette releases, without being mentioned in the release notes. \n The exception to this rule is anything that is documented here. If you find a need for an undocumented utility function in your own work, consider opening an issue requesting that the function you are using be upgraded to documented and supported status.", "breadcrumbs": "[\"Internals for plugins\"]", "references": "[{\"href\": \"https://github.com/simonw/datasette/issues/new\", \"label\": \"opening an issue\"}]"}
{"id": "internals:internals-tracer-trace-child-tasks", "page": "internals", "ref": "internals-tracer-trace-child-tasks", "title": "Tracing child tasks", "content": "If your code uses a mechanism such as asyncio.gather() to execute code in additional tasks you may find that some of the traces are missing from the display. \n You can use the trace_child_tasks() context manager to ensure these child tasks are correctly handled. \n from datasette import tracer\n\nwith tracer.trace_child_tasks():\n results = await asyncio.gather(\n # ... async tasks here\n ) \n This example uses the register_routes() plugin hook to add a page at /parallel-queries which executes two SQL queries in parallel using asyncio.gather() and returns their results. \n from datasette import hookimpl\nfrom datasette import tracer\n\n\n@hookimpl\ndef register_routes():\n async def parallel_queries(datasette):\n db = datasette.get_database()\n with tracer.trace_child_tasks():\n one, two = await asyncio.gather(\n db.execute(\"select 1\"),\n db.execute(\"select 2\"),\n )\n return Response.json(\n {\n \"one\": one.single_value(),\n \"two\": two.single_value(),\n }\n )\n\n return [\n (r\"/parallel-queries$\", parallel_queries),\n ] \n Note that running parallel SQL queries in this way has been known to cause problems in the past , so treat this example with caution. \n Adding ?_trace=1 will show that the trace covers both of those child tasks.", "breadcrumbs": "[\"Internals for plugins\", \"datasette.tracer\"]", "references": "[{\"href\": \"https://github.com/simonw/datasette/issues/2189\", \"label\": \"been known to cause problems in the past\"}]"}
{"id": "internals:internals-tracer", "page": "internals", "ref": "internals-tracer", "title": "datasette.tracer", "content": "Running Datasette with --setting trace_debug 1 enables trace debug output, which can then be viewed by adding ?_trace=1 to the query string for any page. \n You can see an example of this at the bottom of latest.datasette.io/fixtures/facetable?_trace=1 . The JSON output shows full details of every SQL query that was executed to generate the page. \n The datasette-pretty-traces plugin can be installed to provide a more readable display of this information. You can see a demo of that here . \n You can add your own custom traces to the JSON output using the trace() context manager. This takes a string that identifies the type of trace being recorded, and records any keyword arguments as additional JSON keys on the resulting trace object. \n The start and end time, duration and a traceback of where the trace was executed will be automatically attached to the JSON object. \n This example uses trace to record the start, end and duration of any HTTP GET requests made using the function: \n from datasette.tracer import trace\nimport httpx\n\n\nasync def fetch_url(url):\n with trace(\"fetch-url\", url=url):\n async with httpx.AsyncClient() as client:\n return await client.get(url)", "breadcrumbs": "[\"Internals for plugins\"]", "references": "[{\"href\": \"https://latest.datasette.io/fixtures/facetable?_trace=1\", \"label\": \"latest.datasette.io/fixtures/facetable?_trace=1\"}, {\"href\": \"https://datasette.io/plugins/datasette-pretty-traces\", \"label\": \"datasette-pretty-traces\"}, {\"href\": \"https://latest-with-plugins.datasette.io/github/commits?_trace=1\", \"label\": \"a demo of that here\"}]"}
{"id": "internals:internals-tilde-encoding", "page": "internals", "ref": "internals-tilde-encoding", "title": "Tilde encoding", "content": "Datasette uses a custom encoding scheme in some places, called tilde encoding . This is primarily used for table names and row primary keys, to avoid any confusion between / characters in those values and the Datasette URLs that reference them. \n Tilde encoding uses the same algorithm as URL percent-encoding , but with the ~ tilde character used in place of % . \n Any character other than ABCDEFGHIJKLMNOPQRSTUVWXYZ abcdefghijklmnopqrstuvwxyz0123456789_- will be replaced by the numeric equivalent preceded by a tilde. For example: \n \n \n / becomes ~2F \n \n \n . becomes ~2E \n \n \n % becomes ~25 \n \n \n ~ becomes ~7E \n \n \n Space becomes + \n \n \n polls/2022.primary becomes polls~2F2022~2Eprimary \n \n \n Note that the space character is a special case: it will be replaced with a + symbol. \n \n \n \n datasette.utils. tilde_encode s : str str \n \n Returns tilde-encoded string - for example /foo/bar -> ~2Ffoo~2Fbar \n \n \n \n \n \n datasette.utils. tilde_decode s : str str \n \n Decodes a tilde-encoded string, so ~2Ffoo~2Fbar -> /foo/bar", "breadcrumbs": "[\"Internals for plugins\", \"The datasette.utils module\"]", "references": "[{\"href\": \"https://developer.mozilla.org/en-US/docs/Glossary/percent-encoding\", \"label\": \"URL percent-encoding\"}]"}
{"id": "internals:internals-shortcuts", "page": "internals", "ref": "internals-shortcuts", "title": "Import shortcuts", "content": "The following commonly used symbols can be imported directly from the datasette module: \n from datasette import Response\nfrom datasette import Forbidden\nfrom datasette import NotFound\nfrom datasette import hookimpl\nfrom datasette import actor_matches_allow", "breadcrumbs": "[\"Internals for plugins\"]", "references": "[]"}
{"id": "internals:internals-response-set-cookie", "page": "internals", "ref": "internals-response-set-cookie", "title": "Setting cookies with response.set_cookie()", "content": "To set cookies on the response, use the response.set_cookie(...) method. The method signature looks like this: \n def set_cookie(\n self,\n key,\n value=\"\",\n max_age=None,\n expires=None,\n path=\"/\",\n domain=None,\n secure=False,\n httponly=False,\n samesite=\"lax\",\n): ... \n You can use this with datasette.sign() to set signed cookies. Here's how you would set the ds_actor cookie for use with Datasette authentication : \n response = Response.redirect(\"/\")\nresponse.set_cookie(\n \"ds_actor\",\n datasette.sign({\"a\": {\"id\": \"cleopaws\"}}, \"actor\"),\n)\nreturn response", "breadcrumbs": "[\"Internals for plugins\", \"Response class\"]", "references": "[]"}
{"id": "internals:internals-response-asgi-send", "page": "internals", "ref": "internals-response-asgi-send", "title": "Returning a response with .asgi_send(send)", "content": "In most cases you will return Response objects from your own view functions. You can also use a Response instance to respond at a lower level via ASGI, for example if you are writing code that uses the asgi_wrapper(datasette) hook. \n Create a Response object and then use await response.asgi_send(send) , passing the ASGI send function. For example: \n async def require_authorization(scope, receive, send):\n response = Response.text(\n \"401 Authorization Required\",\n headers={\n \"www-authenticate\": 'Basic realm=\"Datasette\", charset=\"UTF-8\"'\n },\n status=401,\n )\n await response.asgi_send(send)", "breadcrumbs": "[\"Internals for plugins\", \"Response class\"]", "references": "[]"}
{"id": "internals:internals-response", "page": "internals", "ref": "internals-response", "title": "Response class", "content": "The Response class can be returned from view functions that have been registered using the register_routes(datasette) hook. \n The Response() constructor takes the following arguments: \n \n \n body - string \n \n The body of the response. \n \n \n \n status - integer (optional) \n \n The HTTP status - defaults to 200. \n \n \n \n headers - dictionary (optional) \n \n A dictionary of extra HTTP headers, e.g. {\"x-hello\": \"world\"} . \n \n \n \n content_type - string (optional) \n \n The content-type for the response. Defaults to text/plain . \n \n \n \n For example: \n from datasette.utils.asgi import Response\n\nresponse = Response(\n \"