BUG: Enable stata files to be written to buffers

Enable support for general file-like objects when exporting stata files

closes #21041

Author: bashtage

doc/source/whatsnew/v0.23.1.txt

@@ -81,7 +81,7 @@ Indexing
 I/O
 ^^^
 
--
+- Bug in :math:`DataFrame.to_stata` which prevented buffers from being directly written to (:issue:`21041`)
 -
 
 Plotting

pandas/core/frame.py

@@ -1774,8 +1774,11 @@ def to_stata(self, fname, convert_dates=None, write_index=True,
 
         Parameters
         ----------
-        fname : str or buffer
-            String path of file-like object.
+        fname : path (string), buffer or path object
+            string, path object (pathlib.Path or py._path.local.LocalPath) or
+            object implementing a binary write() functions. If using a buffer
+            then the buffer will not be automatically closed after the file
+            data has been written.
         convert_dates : dict
             Dictionary mapping columns containing datetime types to stata
             internal format to use when writing the dates. Options are 'tc',

pandas/io/stata.py

@@ -1758,11 +1758,25 @@ def value_labels(self):
         return self.value_label_dict
 
 
-def _open_file_binary_write(fname, encoding):
+def _open_file_binary_write(fname):
+    """
+    Open a binary file or no-op if file-like
+
+    Parameters
+    ----------
+    fname : string path, path object or buffer
+
+    Returns
+    -------
+    file : file-like object
+        File object supporting write
+    own : bool
+        True if the file was created, otherwise False
+    """
     if hasattr(fname, 'write'):
         # if 'b' not in fname.mode:
-        return fname
-    return open(fname, "wb")
+        return fname, False
+    return open(fname, "wb"), True
 
 
 def _set_endianness(endianness):
@@ -1899,7 +1913,9 @@ class StataWriter(StataParser):
     ----------
     fname : path (string), buffer or path object
         string, path object (pathlib.Path or py._path.local.LocalPath) or
-        object implementing a binary write() functions.
+        object implementing a binary write() functions. If using a buffer
+        then the buffer will not be automatically closed after the file
+        is written.
 
         .. versionadded:: 0.23.0 support for pathlib, py.path.
 
@@ -1970,6 +1986,7 @@ def __init__(self, fname, data, convert_dates=None, write_index=True,
         self._time_stamp = time_stamp
         self._data_label = data_label
         self._variable_labels = variable_labels
+        self._own_file = True
         # attach nobs, nvars, data, varlist, typlist
         self._prepare_pandas(data)
 
@@ -2183,9 +2200,7 @@ def _prepare_pandas(self, data):
                 self.fmtlist[key] = self._convert_dates[key]
 
     def write_file(self):
-        self._file = _open_file_binary_write(
-            self._fname, self._encoding or self._default_encoding
-        )
+        self._file, self._own_file = _open_file_binary_write(self._fname)
         try:
             self._write_header(time_stamp=self._time_stamp,
                                data_label=self._data_label)
@@ -2205,7 +2220,13 @@ def write_file(self):
             self._write_file_close_tag()
             self._write_map()
         finally:
-            self._file.close()
+            try:
+                # Some file-like objects might not support flush
+                self._file.flush()
+            except AttributeError:
+                pass
+            if self._own_file:
+                self._file.close()
 
     def _write_map(self):
         """No-op, future compatibility"""
@@ -2374,7 +2395,7 @@ def _prepare_data(self):
 
     def _write_data(self):
         data = self.data
-        data.tofile(self._file)
+        self._file.write(data.tobytes())
 
     def _null_terminate(self, s, as_string=False):
         null_byte = '\x00'
@@ -2641,7 +2662,9 @@ class StataWriter117(StataWriter):
     ----------
     fname : path (string), buffer or path object
         string, path object (pathlib.Path or py._path.local.LocalPath) or
-        object implementing a binary write() functions.
+        object implementing a binary write() functions. If using a buffer
+        then the buffer will not be automatically closed after the file
+        is written.
     data : DataFrame
         Input to save
     convert_dates : dict
@@ -2879,7 +2902,7 @@ def _write_data(self):
         self._update_map('data')
         data = self.data
         self._file.write(b'<data>')
-        data.tofile(self._file)
+        self._file.write(data.tobytes())
         self._file.write(b'</data>')
 
     def _write_strls(self):

pandas/tests/io/test_stata.py

@@ -2,6 +2,7 @@
 # pylint: disable=E1101
 
 import datetime as dt
+import io
 import os
 import struct
 import warnings
@@ -1473,3 +1474,17 @@ def test_invalid_date_conversion(self):
             with pytest.raises(ValueError):
                 original.to_stata(path,
                                   convert_dates={'wrong_name': 'tc'})
+
+    @pytest.mark.parametrize('version', [114, 117])
+    def test_nonfile_writing(self, version):
+        # GH 21041
+        bio = io.BytesIO()
+        df = tm.makeDataFrame()
+        df.index.name = 'index'
+        with tm.ensure_clean() as path:
+            df.to_stata(bio, version=version)
+            bio.seek(0)
+            with open(path, 'wb') as dta:
+                dta.write(bio.read())
+            reread = pd.read_stata(path, index_col='index')
+        tm.assert_frame_equal(df, reread)