Added the 'placeholder' write_csv func, fixes #1542 (#1603)

Added the 'placeholder' write_csv func, fixes #1542

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
 
@@ -18,6 +18,7 @@
 _JInferenceSpecs = jpy.get_type("io.deephaven.csv.InferenceSpecs")
 _JTableHeader = jpy.get_type("io.deephaven.qst.table.TableHeader")
 _JCharset = jpy.get_type("java.nio.charset.Charset")
+_JCsvTools = jpy.get_type("io.deephaven.csv.CsvTools")
 
 
 class Inference(Enum):
@@ -112,4 +113,21 @@ 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:
+    """ Write 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
+    """
+    try:
+        _JCsvTools.writeCsv(table.j_table, False, path, *cols)
+    except Exception as e:
+        raise DHError("write csv failed.") from e