improve UDF docs

Signed-off-by: Runji Wang <wangrunji0408@163.com>

src/udf/python/README.md

@@ -0,0 +1,75 @@
+# RisingWave Python API
+
+This library provides a Python API for creating user-defined functions (UDF) in RisingWave.
+
+Currently, RisingWave supports user-defined functions implemented as external functions.
+Users need to define functions using the API provided by this library, and then start a Python process as a UDF server.
+RisingWave calls the function remotely by accessing the UDF server at a given address.
+
+## Installation
+
+```sh
+pip install risingwave
+```
+
+## Usage
+
+Define functions in a Python file:
+
+```python
+# udf.py
+from risingwave.udf import udf, udtf, UdfServer
+
+# Define a scalar function
+@udf(input_types=['INT', 'INT'], result_type='INT')
+def gcd(x, y):
+    while y != 0:
+        (x, y) = (y, x % y)
+    return x
+
+# Define a table function
+@udtf(input_types='INT', result_types='INT')
+def series(n):
+    for i in range(n):
+        yield i
+
+# Start a UDF server
+if __name__ == '__main__':
+    server = UdfServer(location="0.0.0.0:8815")
+    server.add_function(gcd)
+    server.add_function(series)
+    server.serve()
+```
+
+Start the UDF server:
+
+```sh
+python3 udf.py
+```
+
+To create functions in RisingWave, use the following syntax:
+
+```sql
+create function <name> ( <arg_type>[, ...] )
+    [ returns <ret_type> | returns table ( <column_name> <column_type> [, ...] ) ]
+    language python as <name_defined_in_server>
+    using link '<udf_server_address>';
+```
+
+- The `language` parameter must be set to `python`.
+- The `as` parameter specifies the function name defined in the UDF server.
+- The `link` parameter specifies the address of the UDF server.
+
+For example:
+
+```sql
+create function gcd(int, int) returns int
+language python as gcd using link 'http://localhost:8815';
+
+create function series(int) returns table (x int)
+language python as series using link 'http://localhost:8815';
+
+select gcd(25, 15);
+
+select * from series(10);
+```

src/udf/python/example.py

@@ -33,7 +33,7 @@ def series2(n: int) -> Iterator[tuple[int, str]]:
 
 
 if __name__ == '__main__':
-    server = UdfServer()
+    server = UdfServer(location="0.0.0.0:8815")
     server.add_function(random_int)
     server.add_function(gcd)
     server.add_function(gcd3)

src/udf/python/risingwave/udf.py

@@ -119,7 +119,21 @@ def udf(input_types: Union[List[Union[str, pa.DataType]], Union[str, pa.DataType
         result_type: Union[str, pa.DataType],
         name: Optional[str] = None,) -> Union[Callable, UserDefinedFunction]:
     """
-    Annotation for creating a user-defined function.
+    Annotation for creating a user-defined scalar function.
+
+    Parameters:
+    - input_types: A list of strings or Arrow data types that specifies the input data types.
+    - result_type: A string or an Arrow data type that specifies the return value type.
+    - name: An optional string specifying the function name. If not provided, the original name will be used.
+
+    Example:
+    ```
+    @udf(input_types=['INT', 'INT'], result_type='INT')
+    def gcd(x, y):
+        while y != 0:
+            (x, y) = (y, x % y)
+        return x
+    ```
     """
 
     return lambda f: UserDefinedScalarFunctionWrapper(f, input_types, result_type, name)
@@ -130,20 +144,42 @@ def udtf(input_types: Union[List[Union[str, pa.DataType]], Union[str, pa.DataTyp
          name: Optional[str] = None,) -> Union[Callable, UserDefinedFunction]:
     """
     Annotation for creating a user-defined table function.
+
+    Parameters:
+    - input_types: A list of strings or Arrow data types that specifies the input data types.
+    - result_types A list of strings or Arrow data types that specifies the return value types.
+    - name: An optional string specifying the function name. If not provided, the original name will be used.
+
+    Example:
+    ```
+    @udtf(input_types='INT', result_types='INT')
+    def series(n):
+        for i in range(n):
+            yield i
+    ```
     """
 
     return lambda f: UserDefinedTableFunctionWrapper(f, input_types, result_types, name)
 
 
 class UdfServer(pa.flight.FlightServerBase):
     """
-    UDF server based on Apache Arrow Flight protocol.
-    Reference: https://arrow.apache.org/cookbook/py/flight.html#simple-parquet-storage-service-with-arrow-flight
+    A server that provides user-defined functions to clients.
+
+    Example:
+    ```
+    server = UdfServer(location="0.0.0.0:8815")
+    server.add_function(my_udf)
+    server.serve()
+    ```
     """
+    # UDF server based on Apache Arrow Flight protocol.
+    # Reference: https://arrow.apache.org/cookbook/py/flight.html#simple-parquet-storage-service-with-arrow-flight
+
     _functions: Dict[str, UserDefinedFunction]
 
-    def __init__(self, location="grpc://0.0.0.0:8815", **kwargs):
-        super(UdfServer, self).__init__(location, **kwargs)
+    def __init__(self, location="0.0.0.0:8815", **kwargs):
+        super(UdfServer, self).__init__('grpc://' + location, **kwargs)
         self._functions = {}
 
     def get_flight_info(self, context, descriptor):

src/udf/python/setup.py

@@ -0,0 +1,15 @@
+from setuptools import find_packages, setup
+
+setup(
+    name="risingwave",
+    version="0.0.1",
+    author="RisingWave Labs",
+    description="RisingWave Python API",
+    url="https://github.com/risingwavelabs/risingwave",
+    packages=find_packages(),
+    classifiers=[
+        "Programming Language :: Python",
+        "License :: OSI Approved :: Apache Software License"
+    ],
+    python_requires=">=3.10",
+)