Lecture 4

Functions

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CodeCademy 4.a.

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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?

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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

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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)

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And countup:

def countup(n):if n > 0:

countup(n-1) print "I'm counting down, now at %d." % n

elif n == 0:print "Happy New Year!"

countup(5)countdown(10)

Weird !!!

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And infinitecount:

def infinitecount(n):print "I'm still %d !" % ninfinitecount(n)

infinitecount(10)

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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.

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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.