# lesson_9_ex_2_17_18

```def ex1(x,y,z): #returns (x/y) ** z if y is not equalt to 0
k = -1
if y != 0:
x = float(x)
k = (x/y)**z
else:
print 'Error'
return k

def ex2(s,n): #returns the nth character of a given string, or -1 does not correspond to a character
k =- 1
if n > len(s) or n < 1:
return -1
else:
return s[n-1],n

def ex3(): #returns the product of x and y the first time that is positive along with the number of user's attempts
x = float(raw_input('give 1st number:'))
y = float(raw_input('give 2nd number:'))
counter = 0
while (x * y) >= 0:
print 'error - give again numbers'
print
x = float(raw_input('give again 1st number:'))
y = float(raw_input('give again 2nd number:'))
counter += 1
return (x*y) , counter

#############################################################

n1 = ex1(4,2,3)
n2 = ex1(5,0,10)
print n1 , n2
###########
x1,x2 = ex2('python',3)
print ex2('PAOK',13)
print x1,x2
###########
k = ex3()
print 'the returned product equals to %f and user made %d attempts. '  %(k , k)```

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