Well to begin with, if you want to constantly check your inputs, you are going to have to use a loop. As in, the psuedocode for the algorithm should be:
Loop Begin
Check the value of a and b
If a or b is less than 0 then ask for input again
Otherwise, continue
Please note, that the algorithm has to run at least once.
That is basically how the psuedocode should look like. So, this is a case where you can use a do-while
loop construct. In Python, there isn't something like this, so we emulate it:
import math
def take_in():
a = raw_input("Enter the value of side a -> ")
b = raw_input("Enter the value of side b -> ")
# Trying to convert to a float
try:
a, b = float(a), float(b)
# If successfully converted, then we return
if a > 0 and b > 0:
return a, b
except ValueError:
pass
# If we cannot return, then we return false, with a nice comment
print "Invalid input"
return False
def main():
# Calling the function at least once
valid = take_in()
# While we are not getting valid input, we keep calling the function
while not valid:
# Assigning the value to valid
valid = take_in()
# Breaking the return tuple into a and b
a, b = valid
print math.sqrt(a ** 2 + b ** 2)
if __name__ == '__main__':
main()