Python: Only alert on Python 2 code

since
- Python 3 is ok from 3.7 onwards
- support for Python 3.6 was just dropped
- we do not actually know the minor version of the analysed code
  (only of the extractor)

python/ql/test/2/query-tests/Exceptions/generators/UnguardedNextInGenerator.expected

@@ -0,0 +1,2 @@
+| test.py:5:15:5:22 | ControlFlowNode for next() | Call to next() in a generator |
+| test.py:10:20:10:27 | ControlFlowNode for next() | Call to next() in a generator |

python/ql/test/2/query-tests/Exceptions/generators/UnguardedNextInGenerator.qlref

@@ -0,0 +1 @@
+Exceptions/UnguardedNextInGenerator.ql

python/ql/test/2/query-tests/Exceptions/generators/test.py

@@ -0,0 +1,64 @@
+#Unguarded calls to next()
+
+def bad1(it):
+    while True:
+        yield next(it)
+
+def bad2(seq):
+    it = iter(seq)
+    #Not OK as seq  may be empty
+    raise KeyError(next(it))
+    yield 0
+
+def ok1(seq):
+    #Not a generator
+    it = iter(seq)
+    #Not OK as seq  may be empty
+    raise KeyError(next(it))
+
+def ok2(seq):
+    if seq:
+        it = iter(seq)
+        #OK seq is non-empty so next(it) will not raise StopIteration
+        raise KeyError(next(it))
+    yield 0
+
+def explicit_raise_stop_iter(seq):
+    for i in seq:
+        yield seq
+    raise StopIteration()
+
+def ok3(seq):
+    it = iter(seq)
+    try:
+        yield next(iter)
+    except StopIteration:
+        return
+
+def ok4(seq, ctx):
+    try:
+        with ctx:
+            yield next(iter)
+    except StopIteration:
+        return
+
+#ODASA-6536
+def next_in_comp(seq, fields):
+    seq_iter = iter(seq)
+    values = [ next(seq_iter) if f.attname in NAMES else DEFAULT for f in fields ]
+    return values
+
+def ok5(seq):
+    yield next(iter([]), 'foo')
+
+def ok6(seq):
+    yield next(iter([]), default='foo')    
+
+# Handling for multiple exception types, one of which is `StopIteration`
+# Reported as a false positive in github/codeql#6227
+def ok7(seq, ctx):
+    try:
+        with ctx:
+            yield next(iter)
+    except (StopIteration, MemoryError):
+        return