class Student(object):
    '''A student with a name, age, major, and set of enrolled courses.'''
    
    def __init__(self, name, age, major='undeclared'):
        '''Initializes the student object.'''
        self.name = name
        self.age = age
        self.major = major
        self.courses = set()
        
    
    def add_course(self, course):
        '''Enroll the student in a course, as long
        as the student does not have a full class load already.'''
        if len(self.courses) < 4:
            self.courses.add(course)
        else:
            print('Schedule full, can\'t enroll')
        

    def birthyear(self):
        '''Return the student's year of birth.'''
        return 2016 - self.age


    def switch_major(self, new_major):
        '''Changes the student's major to new_major'''
        self.major = new_major
    
    
    def __str__(self):
        '''Returns a string representation of the student object.'''
        return self.name # return, not print!


class Course:
    '''A class described by a name, an enrollment limit, and a set of enrolled
    students.'''
    
    def __init__(self, name, limit=30):
        '''Creates a new course with the specified name and limit and no
        initial students.'''
        self.name = name
        self.limit = limit
        self.students = set()
    
    def __str__(self):
        '''Return a textual version of the course.'''
        return '{0}, limit {1}, enrollment {2}'.format(self.name,
                                                       self.limit,
                                                       len(self.students))
    
    def has_space(self):
        '''Return whether the course has space for another student.'''
        return len(self.students) < self.limit
    
    
    def add_student(self, student):
        '''Adds the specified student to the course'''
        if self.has_space():
            self.students.add(student)
            # now, add this course to the student's list of courses
            student.add_course(self)
            print('Enrolled', student)
        else:
            print('No room for', student)
        

# some sample Students and Courses

alice = Student('Alice', 18, 'comp sci')
bob = Student('Bob', 19, 'english')
charlie = Student('Charlie', 20)

course1 = Course('Biology 423: Evolution of Squirrels', 10)
course2 = Course('History 130: Computers of the 12th Century', 20)
course3 = Course('Government 250: Galactic Empires', 1)


########################

import math
        
class Point:
    '''Represent an (x, y) coordinate pair.'''
    
    def __init__(self, new_x, new_y):
        '''Set up a new Point object with an x and y value.'''
        self.x = new_x
        self.y = new_y
        
        
    def __str__(self):
        '''Return a string representation of the point object.'''
        return '({0}, {1})'.format(self.x, self.y)
    
    
    def distance_to(self, other_point):
        '''Return the distance from this point to other_point.'''
        x1 = self.x
        y1 = self.y
        x2 = other_point.x
        y2 = other_point.y
        return math.sqrt((x1 - x2) ** 2 + (y1 - y2) ** 2)
    
    
    def distance_origin(self):
        '''Return the distance from this point (aka self) to the origin.'''
        origin = Point(0, 0)
        return self.distance_to(origin)
    
    
    
class LineSegment:
    '''A line segment from one point to another point.'''
    
    def __init__(self, start_point, end_point):
        '''Initializes the line segment by storing the start and endpoints.'''
        self.start_point = start_point
        self.end_point = end_point
        
        
    def __str__(self):
        '''Return a string version of the line segment.'''
        return 'Line from ' + str(self.start_point) + ' to ' + str(self.end_point)
    
    
    def slope(self):
        '''Return the slope of the line segment.'''
        change_y = self.end_point.y - self.start_point.y
        change_x = self.end_point.x - self.start_point.x
        return change_y / change_x
    
    
    def length(self):
        '''Return the length of the line segment.'''
        return self.start_point.distance_to(self.end_point)