Python Part5: Set and exception handling Try except finally

Set

• Unordered collection of unique, immutable objects. 
• Literals: 
• delimited by { and } 
• Single comma separated items. 
• >>> p = {1, 2, 3, 4} 
• >>> p 
• {1, 2, 3, 4} 
• Empty { } makes a dict, so for empty set use the set() constructor. 
• >>> e = set() 
• >>> e 
• set()
• Set() constructor accepts: 
• Iterable series of values. 
• >>> s = set([1, 2, 3, 4]) 
• >>> s 
• {1, 2, 3, 4} 
• Duplicates are discarded. 
• >>> t = [1, 2, 3, 1, 4] 
• >>> set(t) 
• {1, 2, 3, 4} 
• Often used specifically to remove duplicates – not order preserving. 
• Order is arbitrary. 
• >>> for x in {1, 2, 4, 8, 32} 
• print(x)
• Use in and not in operators. 
• >>> q = {2, 9, 6, 4} 
• >>> 3 in q 
• False 
• >>> 3 not in q 
• True 
• Add(item) inserts a single element. 
• >>> k = {2, 4} 
• >>> k 
• {2, 4} 
• >>> k.add(8) 
• >>> k 
• {2, 4, 8}
• Duplicates are silently ignored. 
• >>> k.add(8) 
• >>> k 
• {1, 2, 8} 
• For multiple elements use update(items) passing any iterable series. 
• >>> k.update([9, 10]) 
• >>> k 
• {1, 2, 8, 9, 10} 
• Remove(item) requires that item is present, otherwise raises KeyError. 
• >>> k.remove(9) 
• >>> k 
• {1, 2, 8, 10}
• Discard(item) always succeeds. 
• >>> k.discard(9) 
• Copy set using S.copy() method. 
• >>> j = k.copy() 
• Use constructor. Set(s) 
• >>> m = set(j) 
• Copies are shallows. 
• S1.union(s2) method. 
• Union is commutative.
• s.intersection(t) method 
• Intersection is commutative. 
• s.difference(t) method. 
• Difference is non-commutative. 
• s.symmetric_difference(t) method 
• Symmetric difference is commutative. 
• s.issubset(t) method 
• s.issuperset(t) method. 
• s.isdisjoint(t)

Handle exceptions. Try … except … finally

• try: 
• x = 5 
• except: 
• message = str(sys.exc_info()[1]) 
• x = -1 
• finally: 
• # final-block 
•  x = 0