Circle and line collision detection in python tkinter

I writing a python program in which a circle bounces off of user drawn lines. There are multiple circles that bounce off the wall. For each one, the shortest distance from the center of the circle and the ball should be calculated. I would prefer if this code was very efficient because my current algorithm lags the computer a lot. If point a is the starting point ,and point b is the end point, and point c is the center, and r is the radius, how would I calculate the shortest distance between the ball? This algorithm should also work if the X coordinate of the ball is out of range of x coordinates in segment AB.

Please post python code

Any help would be appreciated!

Here's what I have so far:

lineList is a list with 4 values that contains beginning and end coordinates of the user drawn lines

center is the center of the ball

global lineList, numobjects
        if not(0 in lineList):

            beginCoord = [lineList[0],lineList[1]]

            endCoord = [lineList[2]-500,lineList[3]-500]

            center = [xCoordinate[i],yCoordinate[i]+15]

            distance1 = math.sqrt((lineList[1] - center[1])**2 + (lineList[0] - center[0])**2)

            slope1 = math.tan((lineList[1] - lineList[3]) / (lineList[0] - lineList[2]))

            try:
                slope2 = math.tan((center[1] - beginCoord[1])/(center[0]-beginCoord[0]))

                angle1 = slope2 + slope1

                circleDistance = distance1 * math.sin(angle1)

            except:

                #If the circle is directly above beginCoord
                circleDistance = center[1] - lineList[1]


            global numbounces

            if circleDistance < 2 and circleDistance > -2:

                print(circleDistance)

                b = False

                b2=False

                if xCoordinate[i] < 0:

                    xCoordinate[i] += 1

                    speed1[i] *= -1

                    b=True


                elif xCoordinate[i] > 0:

                    xCoordinate[i] -= 1

                    speed1[i] *= -1

                    b=True


                if yCoordinate[i] < 0:

                    yCoordinate[i] += 1

                    speed2[i] *= -1

                    b2=True


                elif yCoordinate[i] > 0:

                    yCoordinate[i] -= 1

                    speed2[i] *= -1

                    b2=True


                if b and b2:

                 #Only delete the line if the ball reversed directions

                    numbounces += 1

                    #Add a ball after 5 bounces

                    if numbounces % 5 == 0 and numbounces != 0:

                        numobjects = 1

                        getData(numobjects)
                    canvas.delete("line")

                    lineList = [0,0,0,0]