The Matrix notes part 1， python labs

1. <expression1> if <condition> else <expression2>  equals expression i C style: condition ? expression1 ? expression2

2. Set union and intersection: SetA | SetB,   SetA & SetB

3. Mutating a set:

1. S = {1,2,3}; S.update({2,4,5}) // set([1,2,3,4,5])  union
   S.intersecton_update({2,4,5})  // set([2]) intersection
   other functions: copy, add, remove

4. double comprehension {x*y for x in {1,2,3} for y in {2,3,4}}

5. Set is mutable and elements in set are must not mutable.  so {{1,2},3} does not work

6. For dictionary, the key should be mutable: strings, integers, or tuple of strings and integers

7. Construct a dictionary by a comprehension: { k:v for (k,v) in [(3,2),(4,0),(100,1)] }

8. Iterate dictionary by iitems():  [myitem for myitem in mydict.items()] and unpacking [ expression for (k, v) in mydict.items()]

play with GF2：

1. + equals to exclusive or, * equals to ordinary multiplication

2. usage: 

1. encryption (perfect secrecy)

2. network encoding