====== Computer Lab 10, objects and classes I ======

A circle is a 2D geometry shape characterized by the position of its centre and a radius. How can it be represented in Python?
  - Store the centre (//x// and //y// coordinates) and radius (//r//) as separate variables.
  - Store //x//, //y// and //r// as elements in a list or a tuple.
  - Create a new type to represent circles as objects.
The last option is the prefered one. It might be more difficult to implement a class/object but offers much more additional possibilities. 

  * A class starts with a ''class'' keyword:
<code python>
class Circle:
    """represents a circle in 2D space"""
</code>

  * A construction usually initializes object's data. Objects/class data are called **attributes**.
<code python>
def __init__(self, x, y, r):
        self.x = x
        self.y = y
        self.r = r
</code>

  * Now, let's create 2 circles objects:
<code python>
if __name__ == "__main__":
    c1 = Circle(1, 2, 2)
    c2 = Circle(4, 6, 4)
    print(c1.x, c1.y, c1.r)
    print(c2.x, c2.y, c2.r)
</code>

  * Object methods operate on the object. Object/class functions are called **methods**.
<code python>
class Circle:

(...)

    def get_area(self):
        area = 3.14 * (self.r ** 2)
        return area
        
if __name__ == "__main__":
    c1 = Circle(1, 2, 2)
    
    print(c1.get_area())
</code>

  * Create a function (in global scope) which takes 2 circles as arguments and returns True/False if these two circles intersect.
<code python>
def is_intersect(c1, c2):
    """Tells if the two circles intersect or not.
 
    :param c1: Circle object
    :param c2: Circle object
    :return: boolean: True if the c1, c2 intersect, otherwise False
    """
    
if __name__ == "__main__":
    c1 = Circle(1, 2, 2)
    c2 = Circle(4, 6, 4)

    print(is_intersect(c1,c2))
</code>

  * Usually, it is better to include all the functions operating on the objects directly in the corresponding class (thus making them methods):
<code python>
class Circle:

(...)

    def insersects_with(self, other):
        """Tells if this and other circles intersect or not.
    
        :param other: Circle object
        :return: boolean: True if self and other intersect, otherwise False
        """
        
if __name__ == "__main__":
    c1 = Circle(1, 2, 2)
    c2 = Circle(4, 6, 4)
   
    print(c1.insersects_with(c2))      
</code>

  * Next, create a method accepting 2 parameters: //dx// and //dy// that define a shift of the circle's centre. This method should return a copy of itself with a shifted centre.
<WRAP group>
<WRAP half column>
<code python>
class Circle:

(...)

    def get_shifted_copy(self, dx, dy):
        

if __name__ == "__main__":
    c1 = Circle(1, 2, 2)
    print(c1.x, c1.y, c1.r)

    c1_shifted = c1.get_shifted_copy(5, -4)
    print(c1.x, c1.y, c1.r)
    print(c1_shifted.x, c1_shifted.y, c1_shifted.r)
</code>
</WRAP>

<WRAP half column>
<code>
1 2 2
1 2 2
6 -2 2
</code>
</WRAP>
</WRAP>

  * Let's try to use our object in a print() function:
<WRAP group>
<WRAP half column>
<code python>
if __name__ == "__main__":
    c1 = Circle(1, 2, 2)
    print(c1)
</code>
</WRAP>

<WRAP half column>
<code>
<__main__.Circle object at 0x0000029E0C649E50>
</code>
</WRAP>
</WRAP>

  * Well, we don't really care in which address in the memory the //c1// object is located. Let's implement the ''%%__str__(self)%%'' function to overwrite this behaviour:
<WRAP group>
<WRAP half column>
<code python>
class Circle:

(...)
 
    def __str__(self):
        return "Circle: x={}, y={}, r={}".format(self.x, self.y, self.r)

if __name__ == "__main__":
    c1 = Circle(1, 2, 2)
    c2 = Circle(-5, 0, 6)
    print(c1)
    print(c2)
</code>
</WRAP>

<WRAP half column>
<code>
Circle: x=1, y=2, r=2
Circle: x=-5, y=0, r=6
</code>
</WRAP>
</WRAP>

<WRAP center round box 80%>
=== Weekly Homework 10 - Book object ===

Create a class representing a book (catalog card in a library). Your class must have the following structure. Copy-paste the following code and implement the methods:
 

Required filename: ''10_weekly_hw.py''.

<code python>

class Book:
    """represents a book"""

    def __init__(self, title, author, year):
        """
        :param title: string, book title
        :param author: string, book author
        :param year: int, year of publication
        """

    def __str__(self):
        """
        >>> book1 = Book("I, Robot", "Isaac Asimov", 1950)
        >>> print(book1)
        Book: I, Robot by Isaac Asimov (1950)
        >>> book2 = Book("Pride and Prejudice", "Jane Austen", 1813)
        >>> print(book2)
        Book: Pride and Prejudice by Jane Austen (1813)
        """

    def has_same_author(self, other):
        """Compares authors of this and the other book.

        :param other: Book object
        :return: boolean, True if self and other have the same author, otherwise False
        >>> book1 = Book("I, Robot", "Isaac Asimov", 1950)
        >>> book2 = Book("Pride and Prejudice", "Jane Austen", 1813)
        >>> book3 = Book("Sense and Sensibility", "Jane Austen", 1811)
        >>> book1.has_same_author(book3)
        False
        >>> book2.has_same_author(book3)
        True
        """

if __name__ == "__main__":
    import doctest
    doctest.testmod(verbose=True)
</code>

</WRAP>

===== homework =====
<note important>
Solve homework [[courses:be5b33prg:homework:regular:05_fraction_class|05 - Fraction class]] and submit it via Upload system in time! Check the deadline in Upload system.
</note>

<note important>
Solve homework [[courses:be5b33prg:homework:regular:06_prisoners_dilemma:start|06 - Prisoner's dilemma]] (simple player) and submit it via Upload system in time! Check the deadline in Upload system.
</note>