oct 6
asides
- I posted answers to the questions that came up in class on wed on the oct 4 page.
- You can now paste code into the wiki within a <code> ... </code> rather than putting a space before each line.
this is code
- Question: can I import everything (or lots of stuff) all at once?
functions
decisions
If no other questions, start talking about material in chap 7 and 8
if x < 7 :
print "x is small"
else :
print "x is big"
Draw as flow chart.
The "x < 7" is the part I want to talk about (pg 250 etc) in text.
We're now going to have programs that 'branch', which means that
different things can happen. The decision point is a fork in
the road, and which one happens is nearly always a True/False
choice using what are called 'booleans'.
what is 'truth' ?
math :
binary (two things) operations :
integer <operation> integer ==> integer
1 + 2 ===> 3
unary (one thing) operations :
<operation> integer ===> integer
- (1) ===> (-1)
5! ===> 120 (factorial
logic :
'bool' in python is a 'boolean' variable: True or False
have both binary and unary operations with their own algebra
not ( x or not y ) and (not y or z)
boolean operations: not, and, or
values: True, False
also in common use :
if a then b
sometimes written
a implies b
which in itself can also be True or False
comparisons on strings and numbers that give booleans :
<, > , <=, !=, is
Do some examples at the python command line.
Discuss definitions of 'and', 'or' in logic.
Lewis Carroll's 'Symbolic Logic'
e.g. http://home.earthlink.net/~lfdean/carroll/puzzles/logic.html
(1) Every one who is sane can do Logic;
(2) No lunatics are fit to serve on a jury;
(3) None of your sons can do Logic.
What conclusion can be drawn?
Use
a = able to do Logic
b = fit to serve on a jury
c = sane
d = your sons
Express each line as a boolean expression.
Use the rules of boolean algebra to draw a short conclusion.
Answer: None of your sons is fit to serve on a jury.
