Question

I don’t understand why it has two difference result. Please help me, to explain these results.

This is my codesorce:

# coding: iso-8859-2

class Satelite:
    def __init__(self, name, mass=100, speed=0):
        self.name, self.mass, self.speed= name, mass, speed

    def lokes(self, power, time):
        self.speed=self.speed+ power*time/ self.mass

    def energy(self):
        return self.mass* self.speed**2/2

    def out_speed(self):
        print "%s Satelites's speed = %s m/s" %(self.name, self.speed)

# Tesztprogram:

s1=Muhold('Zoe', mass=250, speed=10)

s1.lokes(500,15)
s1.out_speed()
print s1.energy()

s1.lokes(500,15)
s1.out_speed()
print s1.energy()

These are the results:

Zoe Satelite speed= 40 m/s
200000
Zoe Satelite speed= 70 m/s
612500

Answer 1

That’s because you’re modifying a state variable in the middle.

def lokes(self, power, time):
    # this reassigns speed, so next time the function is called, 
    # it will be higher.
    self.speed=self.speed+ power*time/ self.mass

Since speed is changed, and the energy method depends on speed, then the output of energy should change every time you call lokes with values other than 0.