Added the 'placeholder' write_csv func, fixes deephaven#1542

A write_csv func with miniaml number of params as a temporary fillgap
for future full-featured implementation

pyintegration/deephaven2/__init__.py

@@ -17,6 +17,7 @@
 from .dherror import DHError
 from .constants import SortDirection
 from .csv import read as read_csv
+from .csv import write as write_csv
 from .table import empty_table, time_table
 
-__all__ = ["read_csv", "DHError", "time_table", "empty_table", "SortDirection"]
+__all__ = ["read_csv", "write_csv", "DHError", "time_table", "empty_table", "SortDirection"]

pyintegration/deephaven2/column.py

@@ -4,7 +4,7 @@
 from dataclasses import dataclass
 
 
-@dataclass
+@dataclass(frozen=True)
 class Column:
     """ A Column object represents a column in a Deephaven Table. """
     name: str

pyintegration/deephaven2/csv.py

@@ -5,7 +5,7 @@
 Deephaven table out as a CSV file.
 """
 from enum import Enum
-from typing import Dict, Any
+from typing import Dict, Any, List
 
 import jpy
 
@@ -112,4 +112,18 @@ def read(path: str,
 
         return Table(j_table=j_table)
     except Exception as e:
-        raise DHError(e, "read_csv failed") from e
+        raise DHError(e, "read csv failed") from e
+
+
+def write(table: Table, path: str, cols: List[str] = []) -> None:
+    """ WriteC a table to a standard CSV file.
+
+    Args:
+        table (Table): the source table
+        path (str): the path of the CSV file
+        cols (List[str]): the names of the columns to be written out
+
+    Raises:
+        DHError
+    """
+    table.write_csv(path, cols)

pyintegration/deephaven2/table.py

@@ -93,6 +93,12 @@ def __repr__(self):
     def get_dh_table(self):
         return self._j_table
 
+    def write_csv(self: Table, path: str, cols: List[str] = []) -> None:
+        try:
+            _JTableTools.writeCsv(self._j_table, path, *cols)
+        except Exception as e:
+            raise DHError("write csv failed.") from e
+
     @property
     def size(self) -> int:
         """ The current number of rows in the table. """

pyintegration/tests/test_csv.py

@@ -4,7 +4,7 @@
 import unittest
 
 from deephaven2 import dtypes, DHError
-from deephaven2 import read_csv
+from deephaven2 import read_csv, write_csv
 from tests.testbase import BaseTestCase
 
 
@@ -49,6 +49,24 @@ def test_read_error_quote(self):
 
         self.assertIsNotNone(cm.exception.compact_traceback)
 
+    def test_write(self):
+        t = read_csv("tests/data/small_sample.csv")
+        write_csv(t, "./test_write.csv")
+        t_cols = [col.name for col in t.columns]
+        t = read_csv("./test_write.csv")
+        self.assertEqual(t_cols, [col.name for col in t.columns])
+
+        col_names = ["Strings", "Longs", "Floats"]
+        col_types = [dtypes.string, dtypes.long, dtypes.float_]
+        table_header = {k: v for k, v in zip(col_names, col_types)}
+        t = read_csv('tests/data/test_csv.csv', header=table_header)
+        write_csv(t, "./test_write.csv", cols=col_names)
+        t = read_csv('./test_write.csv')
+        self.assertEqual(col_names, [c.name for c in t.columns])
+
+        import os
+        os.remove("./test_write.csv")
+
 
 if __name__ == '__main__':
     unittest.main()