excel configuration

Author: TomAugspurger

pandas/core/config_init.py

@@ -437,43 +437,35 @@ def use_inf_as_na_cb(key):
 writer_engine_doc = """
 : string
     The default Excel writer engine for '{ext}' files. Available options:
-    '{default}' (the default){others}.
-"""
-
-with cf.config_prefix('io.excel'):
-    # going forward, will be additional writers
-    for ext, options in [('xls', ['xlwt']), ('xlsm', ['openpyxl'])]:
-        default = options.pop(0)
-        if options:
-            options = " " + ", ".join(options)
-        else:
-            options = ""
-        doc = writer_engine_doc.format(ext=ext, default=default,
-                                       others=options)
-        cf.register_option(ext + '.writer', default, doc, validator=str)
-
-    def _register_xlsx(engine, other):
-        cf.register_option('xlsx.writer', engine,
-                           writer_engine_doc.format(ext='xlsx', default=engine,
-                                                    others=", '%s'" % other),
-                           validator=str)
-
-_excel_registered = False
-
-
-def _register_excel_engines():
-    global _excel_registered
-
-    if not _excel_registered:
-        with cf.config_prefix('io.excel'):
-            try:
-                # better memory footprint
-                import xlsxwriter  # noqa
-                _register_xlsx('xlsxwriter', 'openpyxl')
-            except ImportError:
-                # fallback
-                _register_xlsx('openpyxl', 'xlsxwriter')
-        _excel_registered = True
+    auto, {others}.
+"""
+
+_xls_options = ['xlwt']
+_xlsm_options = ['openpyxl']
+_xlsx_options = ['openpyxl', 'xlsxwriter']
+
+
+with cf.config_prefix("io.excel.xls"):
+    cf.register_option("writer", "auto",
+                       writer_engine_doc.format(
+                           ext='xls',
+                           others=', '.join(_xls_options)),
+                       validator=str)
+
+with cf.config_prefix("io.excel.xlsm"):
+    cf.register_option("writer", "auto",
+                       writer_engine_doc.format(
+                           ext='xlsm',
+                           others=', '.join(_xlsm_options)),
+                       validator=str)
+
+
+with cf.config_prefix("io.excel.xlsx"):
+    cf.register_option("writer", "auto",
+                       writer_engine_doc.format(
+                           ext='xlsx',
+                           others=', '.join(_xlsx_options)),
+                       validator=str)
 
 
 # Set up the io.parquet specific configuration.

pandas/io/excel.py

@@ -170,6 +170,16 @@ def register_writer(klass):
             _writer_extensions.append(ext)
 
 
+def _get_default_writer(ext):
+    _default_writers = {'xlsx': 'openpyxl', 'xlsm': 'openpyxl', 'xls': 'xlwt'}
+    try:
+        import xlsxwriter  # noqa
+        _default_writers['xlsx'] = 'xlsxwriter'
+    except ImportError:
+        pass
+    return _default_writers[ext]
+
+
 def get_writer(engine_name):
     if engine_name == 'openpyxl':
         try:
@@ -690,10 +700,10 @@ class ExcelWriter(object):
     # ExcelWriter.
     def __new__(cls, path, engine=None, **kwargs):
         # only switch class if generic(ExcelWriter)
-        config_init._register_excel_engines()
 
         if issubclass(cls, ExcelWriter):
-            if engine is None:
+            if engine is None or (isinstance(engine, string_types) and
+                                  engine == 'auto'):
                 if isinstance(path, string_types):
                     ext = os.path.splitext(path)[-1][1:]
                 else:
@@ -702,6 +712,8 @@ def __new__(cls, path, engine=None, **kwargs):
                 try:
                     engine = config.get_option('io.excel.{ext}.writer'
                                                .format(ext=ext))
+                    if engine == 'auto':
+                        engine = _get_default_writer(ext)
                 except KeyError:
                     error = ValueError("No engine for filetype: '{ext}'"
                                        .format(ext=ext))