BUG: read_csv throws UnicodeDecodeError with unicode aliases

see issue pandas-dev#13549
read_csv with engine=c throws error when encoding=UTF_16
or when encoding has _ or caps

Author: nateGeorge

doc/source/whatsnew/v0.19.0.txt

@@ -81,3 +81,4 @@ Performance Improvements
 
 Bug Fixes
 ~~~~~~~~~
+- Bug in ``read_csv()``, where aliases for utf-xx (e.g. UTF-xx, UTF_xx, utf_xx) raised UnicodeDecodeError (:issue:`13549`)

pandas/io/parsers.py

@@ -339,6 +339,10 @@ def _validate_nrows(nrows):
 def _read(filepath_or_buffer, kwds):
     "Generic reader of line files."
     encoding = kwds.get('encoding', None)
+    if encoding is not None:
+        encoding = re.sub('_', '-', encoding).lower()
+        kwds['encoding'] = encoding
+
     skipfooter = kwds.pop('skipfooter', None)
     if skipfooter is not None:
         kwds['skip_footer'] = skipfooter

pandas/tests/io/test_encoding_aliases.py

@@ -0,0 +1,32 @@
+import pandas, os, nose
+
+def test_read_csv():
+    # see gh issue 13549
+    test_encodings = ['utf-16', 'utf_16', 'UTF_16', 'UTF-16']
+    engines = ['c', 'python', None]
+    expected_output = [1]*len(test_encodings)*len(engines)
+    test_output = []
+    path = "test.csv"
+    pandas.DataFrame({"A": [0,1], "B": [2,3]}).to_csv(
+        path, encoding="utf-16")
+
+    for encoding in test_encodings:
+        for engine in engines:
+            try:
+                pandas.io.parsers.read_csv(
+                    path,
+                    engine='c',
+                    encoding=encoding)
+                print(encoding, 'succeeded with engine =', engine)
+                test_output.append(1)
+            except UnicodeDecodeError:
+                print(encoding, 'failed with engine =', engine)
+                test_output.append(0)
+
+    assert (expected_output == test_output)
+
+    os.remove("test.csv")
+
+if __name__ == '__main__':
+    nose.runmodule(argv=[__file__, '-vvs', '-x', '--pdb', '--pdb-failure'],
+                   exit=False)