1. Lecture 4 Functions

2. 2 CodeCademy 4.a.

3. 3 CodeCademy: comments.  As parameter of a function  Second way to introduce variables:  What do max, min, abs do on text strings?  What if you switch the order of a print and return at the end of a function definition?

4. 4  Careful: 18 refers to (* args), but we met this before  Ex. 19: different ways to call functions  Ex. 21: watch the order of evaluation ! LPTHW: 18, 19 and 21

6. 6 Recursive functions: def countdown(n): if n > 0: print "I'm counting down, now at %d." % n countdown(n-1) elif n == 0: print "Happy New Year!" countdown(5)countdown(10)

7. 7 And countup: def countup(n): if n > 0: countup(n-1) countup(n-1) print "I'm counting down, now at %d." % n print "I'm counting down, now at %d." % n elif n == 0: print "Happy New Year!" countup(5)countdown(10) Weird !!!

8. 8 And infinitecount: def infinitecount(n): print "I'm still %d !" % n infinitecount(n)infinitecount(10)

9. 9 Turing complete programming languages.  Allow to compute _any_ computable function.  comparison (==, !=,, =)  + Math (+, -, *, /)  + If  + functions  Are Turing complete.  Anything that can be done with “for”- or “while”- loops, can also be done with recursion.

10. 10 Assignment for next week:  CodeCademy 5.a Lists and Dictionaries (31 min), 5.b A day at the supermarket (28 mins):  LPTHW Ex.32 (9 min), Ex. 34 (11 min)  Ignore all the long comments on ordinals/cardinals.