ENH: Add class to write dta format 117 files

Add export for dta 117 files which add support for long strings
Refactor StataWriter to simplify new writer

closes #16450

Author: bashtage

doc/source/whatsnew/v0.23.0.txt

@@ -450,6 +450,8 @@ Other Enhancements
 - Updated :meth:`DataFrame.to_gbq` and :meth:`pandas.read_gbq` signature and documentation to reflect changes from
   the Pandas-GBQ library version 0.4.0. Adds intersphinx mapping to Pandas-GBQ
   library. (:issue:`20564`)
+- Added new writer for exporting Stata dta files in version 117, ``StataWriter117``.  This format supports exporting strings with lengths up to 2,000,000 characters (:issue:`16450`)
+
 
 .. _whatsnew_0230.api_breaking:
 

pandas/core/frame.py

@@ -1769,7 +1769,8 @@ def to_excel(self, excel_writer, sheet_name='Sheet1', na_rep='',
 
     def to_stata(self, fname, convert_dates=None, write_index=True,
                  encoding="latin-1", byteorder=None, time_stamp=None,
-                 data_label=None, variable_labels=None):
+                 data_label=None, variable_labels=None, version=114,
+                 convert_strl=None):
         """
         A class for writing Stata binary dta files from array-like objects
 
@@ -1801,6 +1802,23 @@ def to_stata(self, fname, convert_dates=None, write_index=True,
 
             .. versionadded:: 0.19.0
 
+        version : {114, 117}
+            dta version to use in the output file.  Version 114 can be used
+            read by Stata 10 and later.  Version 117 can be read by Stata 13
+            or later. Version 114 limits string variables to 244 characters or
+            fewer while 117 allows strings with lengths up to 2,000,000
+            characters.
+
+            .. versionadded:: 0.23.0
+
+        convert_strl : list, optional
+            List of column names to convert to string columns to Stata StrL
+            format. Only available if version is 117.  Storign strings in the
+            StrL format can produce smaller dta files if strings have more than
+            8 characters and values are repeated.
+
+            .. versionadded:: 0.23.0
+
         Raises
         ------
         NotImplementedError
@@ -1832,12 +1850,23 @@ def to_stata(self, fname, convert_dates=None, write_index=True,
         >>> writer = StataWriter('./date_data_file.dta', data, {2 : 'tw'})
         >>> writer.write_file()
         """
-        from pandas.io.stata import StataWriter
-        writer = StataWriter(fname, self, convert_dates=convert_dates,
+        kwargs = {}
+        if version not in (114, 117):
+            raise ValueError('Only formats 114 and 117 supported.')
+        if version == 114:
+            if convert_strl is not None:
+                raise ValueError('strl support is only available when using '
+                                 'format 117')
+            from pandas.io.stata import StataWriter as statawriter
+        else:
+            from pandas.io.stata import StataWriter117 as statawriter
+            kwargs['convert_strl'] = convert_strl
+
+        writer = statawriter(fname, self, convert_dates=convert_dates,
                              encoding=encoding, byteorder=byteorder,
                              time_stamp=time_stamp, data_label=data_label,
                              write_index=write_index,
-                             variable_labels=variable_labels)
+                             variable_labels=variable_labels, **kwargs)
         writer.write_file()
 
     def to_feather(self, fname):