my program is not allowing me to call a variable from a previous function in python

Question

1. My questions are found in the comments below

   def Distanceinput():
       distance = eval(input('Enter a distance (in light years):'))
       print("Velocity Relative time to reach", distance, "light years")
   

   the problem is coming in the following chunk of code where I attempt to use distance from above but it comes back as an error. what can I do to rectify this problem?

   def velocity(velocityPercent):
       DilationFactor = (((1 - (velocityPercent ** 2)) / 10000) ** 0.5)
       perceptualSpeed = (distance * DilationFactor) * 100
       print(velocityPercent, + "% of light", perceptualSpeed, "years.")
   

   the above chunk of code is what is causing problems

   def Time():
       Distanceinput()
       print()
       velocity(10)
       print()
       velocity(25)
       print()
       velocity(50)
       print()
       velocity(75)
       print()
       velocity(90)
       print()
       velocity(99)
       print()
   Time()
   

Answer 1

distance = None
def Distanceinput():
    global distance
    distance = eval(input('Enter a distance (in light years):'))
    print("Velocity Relative time to reach", distance, "light years")

Answer 2

The difference between local and global variables are that local variables may only be accessed inside a function, whereas a global variable may be accessed anywhere throughout the program. Note the names, local (available within a certain area), and global, available everywhere.

def Distanceinput():
    distance = eval(input('Enter a distance (in light years):'))
    print("Velocity Relative time to reach", distance, "light years")

def velocity(velocityPercent):
    DilationFactor = (((1 - (velocityPercent ** 2)) / 10000) ** 0.5)
    perceptualSpeed = (distance * DilationFactor) * 100
    print(velocityPercent, + "% of light", perceptualSpeed, "years.")

Your Distanceinput() is fine. You should return the value though so that it can be used later on in the program. Returning to the local and global variables, distance in velocity(velocityPercent) is considered a local variable. You haven't said anywhere in your function that you needed to access the variable distance that has a value elsewhere in your program. You can accomplish this like so:

# Somewhere at the top of your code...
distance = None

Then, in your function:

def Distanceinput():
    global distance # Says that your function requires the following global variable
    # rest of your code
    return distance # In case you need the output of the function later on.

def velocity(velocityPercent):
    global distance # Again, the same action as above

    DilationFactor = (((1 - (velocityPercent ** 2)) / 10000) ** 0.5)
    perceptualSpeed = (distance * DilationFactor) * 100
    print(velocityPercent, " % of light ", perceptualSpeed, " years.")

Hope it helps! :)

Answer 3

I organized your code a bit differently. Also, if i understood correctly there were some bugs in your velocity function, so i changed it as well.

---

Explanation:

• eval and exec can execute malicious code, so unless you are the only person using your program, try to avoid them. int will work just fine for given problem.
• I created a class, from which you can create different instances. Each time you create an instance you get to input the distance.
• \n is the newline character.
• velocityPercent /= 100. is equivalent to set velocityPercent to its previous value divided by 100. Note that its 100. with a dot, in case you are using python 2.7. Then i removed the /100000 in DilationFactor, and 100 in perceptualSpeed.

One thing you could change is the output of velocity.

class Galaxy(object):

    DISTANCE = 'i like dogs'

    def Distanceinput(self):
        self.DISTANCE = int(input('\nEnter a distance (in light years):'))
        print("Velocity Relative time to reach", self.DISTANCE, "light years")

    def velocity(self, velocityPercent):
        velocityPercent /= 100.
        DilationFactor = ((1 - (velocityPercent ** 2)) ** 0.5)
        perceptualSpeed = self.DISTANCE * DilationFactor
        print(velocityPercent,  "% of light", perceptualSpeed, "years.")

    def Time(self):
        self.Distanceinput()
        print()
        for vel in (10, 25, 50, 75, 90, 99):
            self.velocity(vel)


galaxy_1 = Galaxy()

galaxy_1.Time()

Answer 4

There's 2 way of doing this :

• You work with a global variable
• You pass the variable in parameter

Look here : http://paste2.org/_wpZH5I8m