PyMySQL · methane · Jul 27, 2016 · Jul 26, 2016
diff --git a/pymysql/cursors.py b/pymysql/cursors.py
@@ -30,6 +30,8 @@ class Cursor(object):
    #: Default value of max_allowed_packet is 1048576.
    max_stmt_length = 1024000

+    _defer_warnings = False
+
    def __init__(self, connection):
        '''
        Do not create an instance of a Cursor yourself. Call
@@ -43,6 +45,7 @@ def __init__(self, connection):
        self._executed = None
        self._result = None
        self._rows = None
+        self._warnings_handled = False

    def close(self):
        '''
@@ -86,6 +89,9 @@ def _nextset(self, unbuffered=False):
        """Get the next query set"""
        conn = self._get_db()
        current_result = self._result
+        # for unbuffered queries warnings are only available once whole result has been read
+        if unbuffered:
+            self._show_warnings()
        if current_result is None or current_result is not conn._result:
            return None
        if not current_result.has_next:
@@ -328,22 +334,26 @@ def _do_get_result(self):
        self.description = result.description
        self.lastrowid = result.insert_id
        self._rows = result.rows
+        self._warnings_handled = False

-        if result.warning_count > 0:
-            self._show_warnings(conn)
+        if not self._defer_warnings:
+            self._show_warnings()

-    def _show_warnings(self, conn):
-        if self._result and self._result.has_next:
+    def _show_warnings(self):
+        if self._warnings_handled:
+            return
+        self._warnings_handled = True
+        if self._result and (self._result.has_next or not self._result.warning_count):
            return
-        ws = conn.show_warnings()
+        ws = self._get_db().show_warnings()
        if ws is None:
            return
        for w in ws:
            msg = w[-1]
            if PY2:
                if isinstance(msg, unicode):
                    msg = msg.encode('utf-8', 'replace')
-            warnings.warn(str(msg), err.Warning, 4)
+            warnings.warn(err.Warning(*w[1:3]), stacklevel=4)

    def __iter__(self):
        return iter(self.fetchone, None)
@@ -404,6 +414,8 @@ class SSCursor(Cursor):
    possible to scroll backwards, as only the current row is held in memory.
    """

+    _defer_warnings = True
+
    def _conv_row(self, row):
        return row

@@ -440,6 +452,7 @@ def fetchone(self):
        self._check_executed()
        row = self.read_next()
        if row is None:
+            self._show_warnings()
            return None
        self.rownumber += 1
        return row
@@ -473,6 +486,7 @@ def fetchmany(self, size=None):
        for i in range_type(size):
            row = self.read_next()
            if row is None:
+                self._show_warnings()
                break
            rows.append(row)
            self.rownumber += 1

diff --git a/pymysql/tests/test_DictCursor.py b/pymysql/tests/test_DictCursor.py
@@ -21,7 +21,9 @@ def setUp(self):
        with warnings.catch_warnings():
            warnings.filterwarnings("ignore")
            c.execute("drop table if exists dictcursor")
-        c.execute("""CREATE TABLE dictcursor (name char(20), age int , DOB datetime)""")
+            # include in filterwarnings since for unbuffered dict cursor warning for lack of table
+            # will only be propagated at start of next execute() call
+            c.execute("""CREATE TABLE dictcursor (name char(20), age int , DOB datetime)""")
        data = [("bob", 21, "1990-02-06 23:04:56"),
                ("jim", 56, "1955-05-09 13:12:45"),
                ("fred", 100, "1911-09-12 01:01:01")]

diff --git a/pymysql/tests/test_issues.py b/pymysql/tests/test_issues.py
@@ -4,6 +4,8 @@
 import sys

 import pymysql
+from pymysql import cursors
+from pymysql._compat import text_type
 from pymysql.tests import base
 import unittest2

@@ -486,3 +488,28 @@ def test_issue_363(self):
        # don't assert the exact internal binary value, as it could
        # vary across implementations
        self.assertTrue(isinstance(row[0], bytes))
+
+    def test_issue_491(self):
+        """ Test warning propagation """
+        conn = pymysql.connect(charset="utf8", **self.databases[0])
+
+        with warnings.catch_warnings():
+            # Ignore all warnings other than pymysql generated ones
+            warnings.simplefilter("ignore")
+            warnings.simplefilter("error", category=pymysql.Warning)
+
+            # verify for both buffered and unbuffered cursor types
+            for cursor_class in (cursors.Cursor, cursors.SSCursor):
+                c = conn.cursor(cursor_class)
+                try:
+                    c.execute("SELECT CAST('124b' AS SIGNED)")
+                    c.fetchall()
+                except pymysql.Warning as e:
+                    # Warnings should have errorcode and string message, just like exceptions
+                    self.assertEqual(len(e.args), 2)
+                    self.assertEqual(e.args[0], 1292)
+                    self.assertTrue(isinstance(e.args[1], text_type))
+                else:
+                    self.fail("Should raise Warning")
+                finally:
+                    c.close()