LPTHW Exercises 35 - 39

While loops, Lists, Tuples, and Dictionaries

Review

Boolean Expressions
IF/ELSE Statements
Lists
For Loops
List Indexing and slicing

Exiting a For Loop

We can abruptly exit a for loop or alter it's flow
with break and continue statements respectively

 for i in range(10):     if i == 2:        continue    elif i == 5:        break    print i

WHILE LOOPS

Hybrid of Conditional Statements (IF/ELSE and LOOPS)

 while [boolean expression ==True]:
    # execute this loop body
    # over and over again

While loops are not used very often.
Typically implemented when we want to loop
an undefined number of times

Extra info: List Mutability

Integers, Strings, and Booleans are immutable
This means that their value can't be changed
To update variables, values must be reassigned

   a = "Some random string"   a[0] = "z"    ### This will fail because strings can't be changed   a = "z" + a[1:]     ### we must create a new string and re-assign to a

Lists, on the other hand, are mutable
Can be changed (items added, removed, changed, etc)
sort, append, remove, etc all change the actual list

Extra Info: Tuples

A very similar data type to Lists

A tuple is an ordered sequence of items

Instead of brackets, tuples are created with parentheses

We've seen tuples before with string interpolation

"This is %s an example of %s"  % ("good", "tuples")  my_sample_tuple = (1, "sample", 4, 9)

Difference with lists is that tuples are IMMUTABLE

Exercise 39: Dictionaries

Dictionaries are similar to Lists

They are mutable

Assignment and indexing is similar

They are NOT ordered

Instead they are lookup tables with keys and values

Each key is associated with a value

With the key, you "look up" that value

Exercise 39 Continued

  chores = {"Monday": "rake yard", "Tuesday": "dentist appointment"}  print chores["Monday"]    # dictionaries have built-in functions, just like Lists  print chores.keys()  print chores.items()
  for day, assignment in chores.items():      print "On %s, I will %s" % (day, assignment)  
    chores["Wednesday"] = "wash clothing"
  print chores
  thursday_chore = chores.get("Thursday", "I have nothing planned")  print thursday_chore