1. For loop, definite vs indefinite iteration, range, random

2. For Loop
used in situations where the programmer knows exactly how many times to repeat
a Python for loop is an example of a definite iteration (vs. indefinite iteration)
the easiest way to construct a for loop is with the range function
for i in range(10) : # count from 0 to 9
print i # print from 0 to 9

3. For n in range(r)
When used in a for loop, the range(x) function will execute x times
but the counting starts at 0 and ends at x -1 (for example, if x is 3, then 0, 1, 2)
  0, 1, 2, 3, … x -1
for i in range(10) : # count from 0 to 9
print i + 1 # print from 1 to 10

4. Indefinite vs. Definite Iteration
Compare an indefinite loop to a definite loop
Indefinite loop
Definite loop
name = raw_input(“Name : ")
while (name <> "") :
print name
print "Done"
m = input(“Max : ")
for x in range(m) :
print x + 1

5. Range Parameters Using range(); returns a list of integers
range() can take additional arguments; range(start, stop, step)
Examples of Range
Result
range(4)
[0, 1, 2, 3]
range(1, 5)
[1, 2, 3, 4]
range(0, 15, 3)
[0, 3, 6, 9, 12]
range(7, 0, -1)
[7, 6, 5, 4, 3, 2, 1]

6. Convert Decimal to Binary
the text book version (Unit 3) appears to have some “bugs”
I have provided an alternate version of the pseudocode
as well, note the algorithm only works with numbers within range(255); 0, 1, … 255

7. Algorithm to convert
Some adjustments in the right panel makes the algorithm different from the text (Unit 3)
Convert Decimal -> Binary
Algorithm From Textbook
Suggested Algorithm
read num
for positions p from 7, 6, , do this:
if num ≤ 2p, then
set binary to “0” + binary
otherwise,
set binary to “1” + binary
set num to num – 2p
write binary
read num between 0 & 255
if num < 2p, then
set binary to binary + “0”
set binary to binary + “1”

8. Python implementation
 # Convert Decimal input to Binary
import math
binary = ""
n = input("number n ( ) :")
if (n >= 0 and n <= 255) :
for p in range(7, -1, -1) :
if (n < math.pow(2, p)) :
binary = binary + '0'
else :
binary = binary + '1'
n = n - math.pow(2, p)
print binary

9. Random Numbers
Python has a “random number” module; used to generate random numbers
ref :
randint(a, b) can be used to generate a random integer between a & b; a <= N <= b

10. Use randint Import the random module
Call the randint() function within limits a & b
import random
print random.randint(0, 10)

11. Random sequence
The random module will generate a sequence of random numbers; if for example, randint is call more than once
The sequence will be the same, unless seed is called
import random
random.seed() print random.randint(0, 10)
print random.randint(0, 10)