add jupyter notebook for python mistakes meeting

we might want to use notebooks for these types of meetings where code is shown. e.g. for the prev. python3 new stuff it would have probably made sense.

meetings/mistakes-01032017/Mistakes.ipynb

+%% Cell type:code id: tags:
 
+``` python
+# this can be a shortcut to assign None to multiple variables
+x = y = z = None
+z = 1
+
+print(x,y,z)
 ```
 
+%% Output
 
+    (None, None, 1)
 
+%% Cell type:code id: tags:
 
+``` python
+# BAD: this is probably not what you wanted
+u = i = o = []
+o.append("x")
+
+print(u,i,o)
 ```
 
+%% Output
 
+    (['x'], ['x'], ['x'])
 
+%% Cell type:code id: tags:
 
+``` python
+# BAD: the original list you pass to the method will get updated!
+def my_method(mutable_list=[]):
+    mutable_list.append('x')
+    return mutable_list
+
+# a list out of the my_method scope
+a_list = ['a']
+
+b_list = my_method(mutable_list=a_list)
+
+# a_list get modified!
+print( a_list == b_list, a_list, b_list )
 ```
 
+%% Output
 
+    (True, ['a', 'x'], ['a', 'x'])
 
+%% Cell type:code id: tags:
 
+``` python
 ```