1.7 The Line Segment ADT

A line segment is part of a straight line that is bounded by two endpoints. While line segments are commonly used in geometry, they are also quite useful in computer applications that graphically display data. For example, line segments are commonly used to display data in a line graph and for graphically representing the stops and turns along a route or path on maps. We can define an abstract data type to represent a line segment for use in computer applications.

ADT Definition

Using the Line Segment ADT

To illustrate the use of the abstract data type without knowing how it is implemented, consider the following problem. Compute the total distance of a path created from moves in a game by reading a sequence of 2-D Cartesian coordinates from the user that represents each move in the game. Assume there is at least one move and that all coordinates are in the first quadrant (both coordinates will be non-negative). To indicate the end of the sequence, the user enters a negative x-coordinate. Even though we are not going to display the path of the moves in a graphical application, we can still use the Line Segment ADT to compute the distance between individual moves. A solution for this problem is provided in distance.py program below. This program uses a function that reads and returns the x- and y-coordinates of each move. See the Special Topic later on the page for a refresher on functions that return multiple values.

Special Topic

Returning Multiple Values

Functions in most programming languages can only return a single value. In Python, however, it is common practice to use tuples to return multiple values. For example, suppose we define a function that obtains the date from the user as integer values for the month, day, and year and returns the three values in a tuple: def readDate() :   print("Enter a date:")   month = int(input(" month: "))   day = int(input(" day: "))   year = int(input(" year: "))   return (month, day, year)   # Returns a tuple When the function is called, you can assign the entire tuple to a variable: date = readDate() or you can use a feature of Python known as tuple assignment: (month, day, year) = readDate() Some people prefer to omit the parentheses, making it look as if the function really returned multiple values: return month, day, year Nevertheless, that's still a tuple. If you like, you can also omit the parentheses in the tuple assignment: month, day, year = readDate()