register_function(name=...) argument, closes #458

docs/python-api.rst

@@ -2513,6 +2513,16 @@ You can also use the method as a function decorator like so:
 
     print(db.execute('select reverse_string("hello")').fetchone()[0])
 
+By default, the name of the Python function will be used as the name of the SQL function. You can customize this with the ``name=`` keyword argument:
+
+.. code-block:: python
+
+    @db.register_function(name="rev")
+    def reverse_string(s):
+        return "".join(reversed(list(s)))
+
+    print(db.execute('select rev("hello")').fetchone()[0])
+
 Python 3.8 added the ability to register `deterministic SQLite functions <https://sqlite.org/deterministic.html>`__, allowing you to indicate that a function will return the exact same result for any given inputs and hence allowing SQLite to apply some performance optimizations. You can mark a function as deterministic using ``deterministic=True``, like this:
 
 .. code-block:: python

sqlite_utils/db.py

@@ -367,7 +367,11 @@ class Database:
         return "<Database {}>".format(self.conn)
 
     def register_function(
-        self, fn: Callable = None, deterministic: bool = False, replace: bool = False
+        self,
+        fn: Callable = None,
+        deterministic: bool = False,
+        replace: bool = False,
+        name: Optional[str] = None,
     ):
         """
         ``fn`` will be made available as a function within SQL, with the same name and number
@@ -388,12 +392,13 @@ class Database:
         :param fn: Function to register
         :param deterministic: set ``True`` for functions that always returns the same output for a given input
         :param replace: set ``True`` to replace an existing function with the same name - otherwise throw an error
+        :param name: name of the SQLite function - if not specified, the Python function name will be used
         """
 
         def register(fn):
-            name = fn.__name__
+            fn_name = name or fn.__name__
             arity = len(inspect.signature(fn).parameters)
-            if not replace and (name, arity) in self._registered_functions:
+            if not replace and (fn_name, arity) in self._registered_functions:
                 return fn
             kwargs = {}
             registered = False
@@ -401,15 +406,15 @@ class Database:
                 # Try this, but fall back if sqlite3.NotSupportedError
                 try:
                     self.conn.create_function(
-                        name, arity, fn, **dict(kwargs, deterministic=True)
+                        fn_name, arity, fn, **dict(kwargs, deterministic=True)
                     )
                     registered = True
                 except (sqlite3.NotSupportedError, TypeError):
                     # TypeError is Python 3.7 "function takes at most 3 arguments"
                     pass
             if not registered:
-                self.conn.create_function(name, arity, fn, **kwargs)
+                self.conn.create_function(fn_name, arity, fn, **kwargs)
-            self._registered_functions.add((name, arity))
+            self._registered_functions.add((fn_name, arity))
             return fn
 
         if fn is None:

tests/test_register_function.py

@@ -14,6 +14,15 @@ def test_register_function(fresh_db):
     assert result == "olleh"
 
 
+def test_register_function_custom_name(fresh_db):
+    @fresh_db.register_function(name="revstr")
+    def reverse_string(s):
+        return "".join(reversed(list(s)))
+
+    result = fresh_db.execute('select revstr("hello")').fetchone()[0]
+    assert result == "olleh"
+
+
 def test_register_function_multiple_arguments(fresh_db):
     @fresh_db.register_function
     def a_times_b_plus_c(a, b, c):