Updates

README.md

@@ -78,9 +78,14 @@ Set
 <set> = set()
 <set>.add(<el>)
 <set>.update(<set>)
+<set>.clear()
+```
+
+```python
 <set>  = <set>.union(<set>)
 <set>  = <set>.intersection(<set>)
 <set>  = <set>.difference(<set>)
+<set>  = <set>.symmetric_difference(<set>)
 <bool> = <set>.issubset(<set>)
 <bool> = <set>.issuperset(<set>)
 ```
@@ -499,6 +504,13 @@ class <name>:
         return cls.__name__
 ```
 
+#### Constructor overloading:
+```python
+class C:
+    def __init__(self, a=None):
+        self.a = a
+```
+
 ### Enum
 ```python
 from enum import Enum, auto
@@ -540,6 +552,9 @@ Cutlery = Enum('Cutlery', {'knife': 1, 'fork': 2, 'spoon': 3})
 # Functions can not be values, so they must be enclosed in tuple:
 LogicOp = Enum('LogicOp', {'AND': (lambda l, r: l and r, ),
                            'OR' : (lambda l, r: l or r, )}
+# But 'list(<enum>)' will only work if there is another value in tuple:
+LogicOp = Enum('LogicOp', {'AND': (auto(), lambda l, r: l and r),
+                           'OR' : (auto(), lambda l, r: l or r)}
 ```
 
 ### Copy