[GitHub] [spark] ueshin commented on a diff in pull request #41316: [SPARK-43798][SQL][PYTHON] Support Python user-defined table functions

["ueshin (via GitHub)" <gi...@apache.org>]

ueshin commented on code in PR #41316:
URL: https://github.com/apache/spark/pull/41316#discussion_r1207428719


##########
python/pyspark/worker.py:
##########
@@ -456,6 +456,54 @@ def assign_cols_by_name(runner_conf):
     )
 
 
+def read_udtf(pickleSer, infile, eval_type):
+    num_udtfs = read_int(infile)
+    if num_udtfs != 1:
+        raise RuntimeError("Got more than 1 UDTF")
+
+    # See `PythonUDFRunner.writeUDFs`.
+    num_arg = read_int(infile)
+    arg_offsets = [read_int(infile) for _ in range(num_arg)]
+    num_chained_funcs = read_int(infile)
+    if num_chained_funcs != 1:
+        raise RuntimeError("Got more than 1 chained UDTF")
+
+    handler, return_type = read_command(pickleSer, infile)
+    if not isinstance(handler, type):
+        raise RuntimeError(f"UDTF handler must be a class, but got {type(handler)}.")
+
+    # Instantiate the UDTF class.
+    try:
+        udtf = handler()
+    except Exception as e:
+        raise RuntimeError(f"Failed to init the UDTF handler: {str(e)}") from None
+
+    # Wrap the eval method.
+    if not hasattr(udtf, "eval"):
+        raise RuntimeError("Python UDTF must implement the eval method.")
+
+    def wrap_udtf(f, return_type):
+        if return_type.needConversion():
+            toInternal = return_type.toInternal
+            return lambda *a: map(toInternal, f(*a))
+        else:
+            return lambda *a: f(*a)
+
+    f = wrap_udtf(getattr(udtf, "eval"), return_type)
+
+    def mapper(a):
+        results = tuple(f(*[a[o] for o in arg_offsets]))
+        return results
+
+    # Return an iterator of iterators.
+    def func(_, it):
+        return map(mapper, it)

Review Comment:
   I guess we can call `terminate` here, then we don't need to return `udft`?
   
   ```py
   def func(_, it):
       try:
           yield from map(mapper, it)
       finally:
           if hasattr ...
               udtf.terminate()
   ```
   
   try-finally is necessary if `terminate()` should always be called; otherwise we can omit it.



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