docs(bigframes): Add docs to the to_csv methods of dataframe and series (#16570)

sycai · web-flow · commit a8fccefd868e · 2026-04-07T10:23:09.000-05:00
Also reformatted two files under `rewrite/` dir to make the linter
happy.


Fixes b/498602137 🦕
diff --git a/packages/bigframes/bigframes/core/rewrite/__init__.py b/packages/bigframes/bigframes/core/rewrite/__init__.py
@@ -18,6 +18,7 @@
 from bigframes.core.rewrite.identifiers import remap_variables
 from bigframes.core.rewrite.implicit_align import try_row_join
 from bigframes.core.rewrite.legacy_align import legacy_join_as_projection
+from bigframes.core.rewrite.nullity import simplify_join
 from bigframes.core.rewrite.order import bake_order, defer_order
 from bigframes.core.rewrite.pruning import column_pruning
 from bigframes.core.rewrite.scan_reduction import (
@@ -33,7 +34,6 @@
     rewrite_range_rolling,
     simplify_complex_windows,
 )
-from bigframes.core.rewrite.nullity import simplify_join
 
 __all__ = [
     "as_sql_nodes",
diff --git a/packages/bigframes/bigframes/core/rewrite/nullity.py b/packages/bigframes/bigframes/core/rewrite/nullity.py
@@ -14,9 +14,10 @@
 
 from __future__ import annotations
 
-from bigframes.core import nodes
 import dataclasses
 
+from bigframes.core import nodes
+
 
 def simplify_join(node: nodes.BigFrameNode) -> nodes.BigFrameNode:
     """Simplify a join node by removing nullity checks."""
diff --git a/packages/bigframes/third_party/bigframes_vendored/pandas/core/frame.py b/packages/bigframes/third_party/bigframes_vendored/pandas/core/frame.py
@@ -553,6 +553,49 @@ def to_parquet(
         """
         raise NotImplementedError(constants.ABSTRACT_METHOD_ERROR_MESSAGE)
 
+    def to_csv(
+        self,
+        path_or_buf=None,
+        sep=",",
+        *,
+        header: bool = True,
+        index: bool = True,
+        allow_large_results: Optional[bool] = None,
+    ) -> Optional[str]:
+        """
+        Write object to a comma-separated values (csv) file.
+
+        **Examples:**
+
+            >>> import bigframes.pandas as bpd
+
+            >>> df = bpd.DataFrame({'col1': [1, 2], 'col2': [3, 4]})
+            >>> df.to_csv()
+            \',col1,col2\\n0,1,3\\n1,2,4\\n\'
+
+        Args:
+            path_or_buf (str, path object, file-like object, or None, default None):
+                String, path object (implementing os.PathLike[str]), or file-like object
+                implementing a write() function. If None, the result is returned as a string.
+                If a non-binary file object is passed, it should be opened with newline='',
+                disabling universal newlines. If a binary file object is passed,
+                mode might need to contain a 'b'.
+                Must contain a wildcard character '*' if this is a GCS path.
+            sep (str, default ','):
+                String of length 1. Field delimiter for the output file.
+            header (bool, default True):
+                Write out the column names.
+            index (bool, default True):
+                Write row names (index).
+            allow_large_results (bool, default None):
+                If not None, overrides the global setting to allow or disallow large
+                query results over the default size limit of 10 GB.
+
+        Returns:
+            If path_or_buf is None, returns the resulting csv format as a string. Otherwise returns None.
+        """
+        raise NotImplementedError(constants.ABSTRACT_METHOD_ERROR_MESSAGE)
+
     def to_dict(
         self,
         orient: Literal[
diff --git a/packages/bigframes/third_party/bigframes_vendored/pandas/core/series.py b/packages/bigframes/third_party/bigframes_vendored/pandas/core/series.py
@@ -549,6 +549,49 @@ def to_markdown(
         """
         raise NotImplementedError(constants.ABSTRACT_METHOD_ERROR_MESSAGE)
 
+    def to_csv(
+        self,
+        path_or_buf=None,
+        sep=",",
+        *,
+        header: bool = True,
+        index: bool = True,
+        allow_large_results: Optional[bool] = None,
+    ) -> Optional[str]:
+        """
+        Write object to a comma-separated values (csv) file.
+
+        **Examples:**
+
+            >>> import bigframes.pandas as bpd
+
+            >>> s = bpd.Series([1,2,3], name='my_series')
+            >>> s.to_csv()
+            \',my_series\\n0,1\\n1,2\\n2,3\\n\'
+
+        Args:
+            path_or_buf (str, path object, file-like object, or None, default None):
+                String, path object (implementing os.PathLike[str]), or file-like object
+                implementing a write() function. If None, the result is returned as a string.
+                If a non-binary file object is passed, it should be opened with newline='',
+                disabling universal newlines. If a binary file object is passed,
+                mode might need to contain a 'b'.
+                Must contain a wildcard character '*' if this is a GCS path.
+            sep (str, default ','):
+                String of length 1. Field delimiter for the output file.
+            header (bool, default True):
+                Write out the column names.
+            index (bool, default True):
+                Write row names (index).
+            allow_large_results (bool, default None):
+                If not None, overrides the global setting to allow or disallow large
+                query results over the default size limit of 10 GB.
+
+        Returns:
+            If path_or_buf is None, returns the resulting csv format as a string. Otherwise returns None.
+        """
+        raise NotImplementedError(constants.ABSTRACT_METHOD_ERROR_MESSAGE)
+
     def to_dict(
         self,
         into: type[dict] = dict,
