sequence.txt
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Lists and tuples

Along with dictionaries, the heart of Python!
 We'll have go beyond the book in lectures, readings

Like strings, lists and tuples are sequences and iterables
 sequence: s + t, and s * n operators, indices s[i], s[i:j]
 iterable: for x in s:...

Unlike strings, lists and tuples can have any type in each element, can be nested
 [ 1, "two", [2, "three", (4, "five")] ]

Like strings, tuples are immutable

UNLIKE strings, lists are mutable.  LISTS ARE MUTABLE!!
  s[i] = x # works for lists
  s + t returns a new list, leaves s and t unchanged (like strings)
  s.extend(t), s.append(t), s.sort() all return None and mutate list s

Lists and strings
  s.split(c) splits string s on separator c, returns list of strings
  c.join(l) joins list of strings l, returns one string with separator c


















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Lists: aliasing, sharing, copy

  l2 = l1 makes l2 an alias for l2, both see same list object, updating l1 changes l2
  l3 = copy(l1) or l3 = l1[i:j] or l3 = [:] makes a separate, distinct copy
  Can mutate list contents from within a function



















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Lists: queues

 Lists can model queues
   Add items at end, remove items from front (see traffic.py)

 Use list of strings to model line of vehicles - 
  functions for arrive, depart, notice we can update list from within functions.  

 In main simulator, note use of arrive and depart function objects -
  Can do other things with functions besides call them
  Can put in tuples, assign to variables, test equality, look up names

 Review __name__ == '__main__' convention

 Review default args
 
 Run it with several values of n














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Lists of tuples: relational database

 List of tuples is a ubiquitous data structure

 Relational database (see phones.py)

 List comprehensions make a mini query language

 In general
  [ pattern for item in source if condition ]

 Example: find the names of all the people who have phones in the physics dept

  [ name for (name, phone) in phones if physics_dept(phone) ]

  Conditon: physics_dept returns True or False if phone number in range
  Note tuple assignment: (name, phone) in phones







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List of tuples: graphs

  Network data structure (see route.py, traverse.py)

  Nodes, edges are pairs of nodes (tuples), edge list defines graph

  Directed graph, edges point one way, draw arrows

  check path by checking that successive pairs of nodes are in graph

  route.py:
   *graph parameter gathers however many arguments into a tuple (see 12.4,136)
    path[i:i+2] is slice within path

  traverse.py
    find path through graph
    list comprehensions here are just scratch data