add on_connect to MySQLDialect_pyodbc

Fixes: #4876

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### Description
add on_connect to MySQLDialect_pyodbc to specify Unicode encoding/decoding settings for the pyodbc connection

### Checklist
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This pull request is:

- [ ] A documentation / typographical error fix
	- Good to go, no issue or tests are needed
- [x] A short code fix
	- please include the issue number, and create an issue if none exists, which
	  must include a complete example of the issue.  one line code fixes without an
	  issue and demonstration will not be accepted.
	- Please include: `Fixes: #<issue number>` in the commit message
	- please include tests.   one line code fixes without tests will not be accepted.
- [ ] A new feature implementation
	- please include the issue number, and create an issue if none exists, which must
	  include a complete example of how the feature would look.
	- Please include: `Fixes: #<issue number>` in the commit message
	- please include tests.

**Have a nice day!**

Closes: #4885
Pull-request: https://github.com/sqlalchemy/sqlalchemy/pull/4885
Pull-request-sha: 58f6176331702b72f3ea8342c93be6fe9a3db26f

Change-Id: If05c1cf8fb1d8efebcf809bdefe40242118d763f

1 files changed, 24 insertions, 0 deletions

diff --git a/lib/sqlalchemy/dialects/mysql/pyodbc.py b/lib/sqlalchemy/dialects/mysql/pyodbc.py
index 6866c3f42..9a18b5090 100644
--- a/lib/sqlalchemy/dialects/mysql/pyodbc.py
+++ b/lib/sqlalchemy/dialects/mysql/pyodbc.py
@@ -23,6 +23,7 @@
 """
 
 import re
+import sys
 
 from .base import MySQLDialect
 from .base import MySQLExecutionContext
@@ -86,5 +87,28 @@ class MySQLDialect_pyodbc(PyODBCConnector, MySQLDialect):
         else:
             return None
 
+    def on_connect(self):
+        super_ = super(MySQLDialect_pyodbc, self).on_connect()
+
+        def on_connect(conn):
+            if super_ is not None:
+                super_(conn)
+
+            # declare Unicode encoding for pyodbc as per
+            #   https://github.com/mkleehammer/pyodbc/wiki/Unicode
+            pyodbc_SQL_CHAR = 1  # pyodbc.SQL_CHAR
+            pyodbc_SQL_WCHAR = -8  # pyodbc.SQL_WCHAR
+            if sys.version_info.major > 2:
+                conn.setdecoding(pyodbc_SQL_CHAR, encoding='utf-8')
+                conn.setdecoding(pyodbc_SQL_WCHAR, encoding='utf-8')
+                conn.setencoding(encoding='utf-8')
+            else:
+                conn.setdecoding(pyodbc_SQL_CHAR, encoding='utf-8')
+                conn.setdecoding(pyodbc_SQL_WCHAR, encoding='utf-8')
+                conn.setencoding(str, encoding='utf-8')
+                conn.setencoding(unicode, encoding='utf-8')
+
+        return on_connect
+
 
 dialect = MySQLDialect_pyodbc