[Python] Improve python API (#8781)

* Fix generate_code script path

* [Python] Make StartVector public

Make StartVector vector public since it is already being used in
generated code

* [Python] Improve vector creation for Python API

Makes Python API for vectors cleaner like Rust and Swift

---------

Co-authored-by: Derek Bailey <derekbailey@google.com>

tests/service_test_generated.py

@@ -2,61 +2,56 @@
 
 # namespace: example
 
-from typing import Any
 import flatbuffers
-
-
 class HelloRequest(object):
-  __slots__ = ['_tab']
+    __slots__ = ['_tab']
 
-  @classmethod
-  def GetRootAs(cls, buf, offset: int = 0):
-    n = flatbuffers.encode.Get(flatbuffers.packer.uoffset, buf, offset)
-    x = HelloRequest()
-    x.Init(buf, n + offset)
-    return x
+    @classmethod
+    def GetRootAs(cls, buf, offset=0):
+        n = flatbuffers.encode.Get(flatbuffers.packer.uoffset, buf, offset)
+        x = HelloRequest()
+        x.Init(buf, n + offset)
+        return x
 
-  @classmethod
-  def GetRootAsHelloRequest(cls, buf, offset=0):
-    """This method is deprecated. Please switch to GetRootAs."""
-    return cls.GetRootAs(buf, offset)
+    @classmethod
+    def GetRootAsHelloRequest(cls, buf, offset=0):
+        """This method is deprecated. Please switch to GetRootAs."""
+        return cls.GetRootAs(buf, offset)
+    # HelloRequest
+    def Init(self, buf, pos):
+        self._tab = flatbuffers.table.Table(buf, pos)
 
-  # HelloRequest
-  def Init(self, buf: bytes, pos: int):
-    self._tab = flatbuffers.table.Table(buf, pos)
+def HelloRequestStart(builder):
+    builder.StartObject(0)
 
+def HelloRequestEnd(builder):
+    return builder.EndObject()
 
-def HelloRequestStart(builder: flatbuffers.Builder):
-  builder.StartObject(0)
-
-
-def HelloRequestEnd(builder: flatbuffers.Builder) -> int:
-  return builder.EndObject()
 
 
 class HelloResponse(object):
-  __slots__ = ['_tab']
+    __slots__ = ['_tab']
 
-  @classmethod
-  def GetRootAs(cls, buf, offset: int = 0):
-    n = flatbuffers.encode.Get(flatbuffers.packer.uoffset, buf, offset)
-    x = HelloResponse()
-    x.Init(buf, n + offset)
-    return x
+    @classmethod
+    def GetRootAs(cls, buf, offset=0):
+        n = flatbuffers.encode.Get(flatbuffers.packer.uoffset, buf, offset)
+        x = HelloResponse()
+        x.Init(buf, n + offset)
+        return x
 
-  @classmethod
-  def GetRootAsHelloResponse(cls, buf, offset=0):
-    """This method is deprecated. Please switch to GetRootAs."""
-    return cls.GetRootAs(buf, offset)
+    @classmethod
+    def GetRootAsHelloResponse(cls, buf, offset=0):
+        """This method is deprecated. Please switch to GetRootAs."""
+        return cls.GetRootAs(buf, offset)
+    # HelloResponse
+    def Init(self, buf, pos):
+        self._tab = flatbuffers.table.Table(buf, pos)
 
-  # HelloResponse
-  def Init(self, buf: bytes, pos: int):
-    self._tab = flatbuffers.table.Table(buf, pos)
+def HelloResponseStart(builder):
+    builder.StartObject(0)
+
+def HelloResponseEnd(builder):
+    return builder.EndObject()
 
 
-def HelloResponseStart(builder: flatbuffers.Builder):
-  builder.StartObject(0)
 
-
-def HelloResponseEnd(builder: flatbuffers.Builder) -> int:
-  return builder.EndObject()