def sep() :
	sepstr = "-" * 75
	print sepstr

secno = 0 # Keeps track of the section number.

def header(sectitle) :
	global secno
	secno += 1
	print
	sep()
	print "%5d. %s" % (secno, sectitle)
	sep()
	print

def pause() :
	raw_input()

def bigpause() :
	print
	raw_input("press enter to continue")
	print "\n" * 24

# Tuples
print "Press enter at pauses."
pause()

#----------------------------------------------------------------
header("Tuples")
tuple1 = (2, 5.4, "some object")
tuple2 = (["a", "list", "of", "words"], ("another", "tuple"))
print tuple1
print tuple2
print "Second elemeent of the first tuple1 : ", tuple1[1]
print "First element of the second element of tuple2 : ", tuple2[1][0]

#-----------------------------------------------------------------
pause()
# However modifying a tuple is not allowed. Uncomment the following lines
# one by one to see for yourself :
#
# tuple1.append('a')
# del tuple2[0]
# tuple2[0] = "same"

# However you can reassign the whole tuple
tuple2 = ("new", "tuple")
print "New tuple2 :", tuple2
# You can add two tuples
print tuple1 + tuple2

#---------------------------------------------------------------------
pause()
# This gives a "hack" to append to tuples.
tuple2 = tuple2 + ("appended", "words")
print "Appended tuple2 :", tuple2

#-------------------------------------------------------------------
# As we saw last time, we can assign tuples:
(a, b) = (2, 3)
print "Tuple assignment : a =", a, ","
print "                   b =", b, "."

# Or you can forget the parenthesis :
c, d = 5, 6
print "Second tuple assignemnt : c = %d, d = %d." % (c, d)

bigpause()

# elif
header("elif")
# In one of the lab sessions we had a bunch of nested ifs. elif is a more
# elegant way of handling that.
# Suppose you want to say a number is positive negative or zero,
n = -5 # n = input("No : ")
if n > 0 :
	print "n = %d is positive." % n
elif n < 0 :
	print "n = %d is negative." % n
else :
	print "n is zero."

#------------------------------------------------------
pause()

# Another example
ans = "yes"
# ans = input("Do you like pears? (valid answers : yes/no/what) : ")
if ans == "yes" :
	print "You should try poached pears."
elif ans == "no" :
	print "Too bad. Do you like apples?"
elif ans == "what" :
	print "Google pear."
else :
	print "Invalid answer."

bigpause()

# functions
header("functions")

# Function to compute nth power of a float. 
def my_power(x, n) :
	x = float(x)
	if n == 0 :
		pow = 1
	elif n > 0 :
		pow = 1
		for i in range(n) :
			pow *= x
	elif n < 0 :
		pow = 1.0
		for i in range(-n) :
			pow /= x
	else :
		print "Really?"

	return pow

print "2 ** 3 =", my_power(2, 3)
print "2 ** -3 =", my_power(2, -3)
print "0 ** -0 =", my_power(0, -0)

#----------------------------------------------------------
pause()
# Second way to do the same thing.
import math
def my_power2(x, n) :
	if n == 0 :
		pow = 1
	elif x == 0 and n != 0 :
		pow = 0
	else :
		pow = math.exp(n * math.log(x))

	return pow
	
print "2 ** 3 =", my_power2(2, 3)
print "2 ** -3 =", my_power2(2, -3)
print "0 ** -0 =", my_power2(0, -0)
			
pause()
# computing mean and standard deviation
lst_data = [100.0, 50.5, 23.5, 23.4, 9.4, 434.5]

def mean(list_of_nos) :
	sum = 0
	for number in list_of_nos :
		sum += number
	mean = float(sum) / len(list_of_nos)
	return mean

print "Mean =", mean(lst_data)

def sd(list_of_nos) :
	sumdev = 0.0
	m = mean(list_of_nos)
	for no in list_of_nos :
		sumdev += (no - m) * (no - m)
	stdev = math.sqrt(sumdev / len(list_of_nos))
	return stdev

print "s.d. =", sd(lst_data)

# Another formula for s.d.
def sd2(list_of_nos) :
	sumsq = 0
	sumval = 0
	for no in list_of_nos :
		sumval += no
		sumsq += no * no
	stdevsq = (sumsq - 1.0/len(list_of_nos) * sumval * sumval)/len(list_of_nos)
	stdev = math.sqrt(stdevsq)
	return stdev

print "s.d. by the second function=", sd2(lst_data)