Lesson 8 Notes: Recursion, Fruitful Functions, and More

• Preview …
  • Notes from recent work
  • Recycling Variables
  • Recursion
  • Functions that Give Back
  • Logical Operators and Boolean values
  • Notes on Program Development
• Review
• Notes From Recent Work
  • To print without space, concatenate:
  • print x+y+z
  • End all "if…elif" sequences with an "else."
  • To reuse a set of code, make it a function.
  • Think more to work less.
  • Avoid nesting "if" statements
  • Test code rigorously; test all scenarios and try to break the program.
• Recycling Variables
  • Once a variable is created, its value can be reassigned.
  • Example:
    card_value = card1+card2
if hit = = yes:
    card_value=card1+card2+card3
else:
   pass
print card_value
• Recursion
  • Recursion is a function calling itself
  • Recursion allows function to be repeated
  • Example:
    def count(x):
   x = x+1
   print x
   count(x)
  • If function never stops, it is called an "infinite recursion"
• Whoa!
  • To prevent infinite recursion, create a "base case".
  • "Base case" is the condition that will cause the function to stop calling itself
  • Example:
    def count(x):
if x <100:
    x = x+1
    print x
    count(x)
else:
   return
• Functions that Give Back
  • Functions can be created that return a value to the program that calls it.
  • Example:
    def add_it(x,y):
   new = x + y
   return new
sum = add_it(5,6)
• Logical Operators
  • Conditional tests can be rolled together using keywords and, or, not
  • and : Both conditions must be met for test to be "true".
  • or : Either condition must be met for test to be "true".
  • not : Tests true if condition is not met.
  • With all conditional tests, Boolean results apply:
    • true = = 1
    • false = = 0 (or !=1)
• Logical Operator Examples
  • if x>0 and x<10:
  • if y>0 and x>0:
  • if pwd=="code" or pwd=="monster":
  • if y>0 or x<0:
  • if not(x<y):
  • if x>y or not(x<0):
• Alternative and Test
  • When testing values for < or >, these tests can be written as one test.
  • Example:
    if 0<x<100:
if 1000>= x >= 0:
• Developing Programs
  • Start by writing in your own words what the program should do.
  • Translate this description into a series of steps in your own words.
  • For each step, translate your words into Python code.
  • Have code print variables to test that they are giving the values you expect.
    Example: print "Num1 =", num1
• Review
  • What is infinite recursion and how can it be avoided?
  • How do you make a function return a value to the main program?
  • What are "logical operators"?
  • What Boolean result is given for true/false?