Documentation for derive_named_parameters()

Closes #2284

Refs simonw/datasette-write#7 (comment)

datasette/utils/__init__.py

@@ -18,12 +18,14 @@
 import types
 import secrets
 import shutil
-from typing import Iterable, Tuple
+from typing import Iterable, List, Tuple
 import urllib
 import yaml
 from .shutil_backport import copytree
 from .sqlite import sqlite3, supports_table_xinfo
 
+if typing.TYPE_CHECKING:
+    from datasette.database import Database
 
 # From https://www.sqlite.org/lang_keywords.html
 reserved_words = set(
@@ -1130,7 +1132,13 @@ class StartupError(Exception):
 _re_named_parameter = re.compile(":([a-zA-Z0-9_]+)")
 
 
-async def derive_named_parameters(db, sql):
+@documented
+async def derive_named_parameters(db: "Database", sql: str) -> List[str]:
+    """
+    Given a SQL statement, return a list of named parameters that are used in the statement
+
+    e.g. for ``select * from foo where id=:id`` this would return ``["id"]``
+    """
     explain = "explain {}".format(sql.strip().rstrip(";"))
     possible_params = _re_named_parameter.findall(sql)
     try:

docs/internals.rst

@@ -1256,6 +1256,15 @@ Utility function for calling ``await`` on a return value if it is awaitable, oth
 
 .. autofunction:: datasette.utils.await_me_maybe
 
+.. _internals_utils_derive_named_parameters:
+
+derive_named_parameters(db, sql)
+--------------------------------
+
+Derive the list of named parameters referenced in a SQL query, using an ``explain`` query executed against the provided database.
+
+.. autofunction:: datasette.utils.derive_named_parameters
+
 .. _internals_tilde_encoding:
 
 Tilde encoding