Rapid GUI Programming with Python and Qt

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Rapid GUI Programmingwith Python and Qt

Classes and ModulesBy

Raed S. Rasheed

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Classes and Modules

Python fully supports procedural and object-oriented programming

The syntax for creating a class is simple:

class className(base_classes):suite

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Creating Instances

• Python has the __new__() special method which is called to construct an object, • the __init__() special method which is called to initialize a newly constructed object.• When an object is about to be garbage-collected its __del__() special method is

called, with self as its only argument.We will create one that stores a string (the name of a kind of chair) and a number (how many legs the chair has):

class Chair(object):"""This class represents chairs."""

def __init__(self, name, legs=4):self.name = nameself.legs = legs

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Creating Instances

To create an instance of a class, we use the following syntax:instance = className(arguments)

for example:chair1 = Chair("Barcelona")chair2 = Chair("Bar Stool", 1)

Since the attributes are public, they can be read or assigned to using the dot (.) operator; for example:print chair2.name will print “Bar Stool”, and chair1.legs = 2 will change chair1’s legs attribute’s value from 4 to 2.

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Methods and Special Methodsclass Rectangle(object):

def __init__(self, width, height):self.width = widthself.height = height

def getWidth(self):return self.width

def setWidth(self, width):self.width = width

def getHeight(self):return self.height

def setHeight(self, height):self.height = height

def area(self):return self.getWidth() * self.getHeight()

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Methods and Special Methods

rect = Rectangle(50, 10)print rect.area() # Prints "500"rect.setWidth(20)

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property() function

class Rectangle(object):def __init__(self, width, height):

self.width = widthself.height = height

def _area(self):return self.width * self.height

area = property(fget=_area)

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rect = Rectangle(5, 4)print rect.width, rect.height, rect.area # Prints (5, 4, 20)rect.width = 6

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def _width(self):return self.__width

def _setWidth(self, width):# Perform some computationself.__width = width

width = property(fget=_width, fset=_setWidth)

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class Rectangle(object):def __init__(self, width, height):

self.__width = widthself.__height = height

def _area(self):return self.__width * self.__height

area = property(fget=_area)def _height(self):

return self.__heightdef _setHeight(self, height):

self.__height = heightheight = property(fget=_height, fset=_setHeight)

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def _width(self): return self.__width

def _setWidth(self, width): self.__width = width

width = property(fget=_width, fset=_setWidth) def __cmp__(self, other):

return cmp(self.area, other.area)def __nonzero__(self):

return self.__width or self.__heightdef __repr__(self):

return "Rectangle(%d, %d)" % (self.__width, self.__height)

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print ("Starting..\n")rect1 = Rectangle(4,5)print ("Area is [",rect1.area,"]")print ("Set width to [ 7 ] and height to [ 2 ]")rect1.width = 7rect1.height = 2print ("Now area is [",rect1.area,"]")print ("\nFinishing..")

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Output:-

Starting..

Area is [ 20 ]Set width to [ 7 ] and height to [ 2 ]Now area is [ 14 ]

Finishing..

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Methods and Special MethodsMethod Syntax Description__init__(self, args) x = X() Initializes a newly created instance__call__(self, args) x() Makes instances callable, that is,turnsthem into functors. The args are optional.__cmp__(self, other) x == yx < y# etc Returns -1 if self < other, 0 if they are equal, and 1 otherwise. If __cmp__() isimplemented, it will be used for any comparison operators that are not explicitly implemented.__eq__(self, other) x == y Returns True if x is equal to y__ne__(self, other) x != y Returns True if x is not equal to y__le__(self, other) x <= y Returns True if x is less than or equal to y

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Method Syntax Description__lt__(self, other) x < y Returns True if x is less than y__ge__(self, other) x >= y Returns True if x is greater than orequal to y__gt__(self, other) x > y Returns True if x is greater than y__nonzero__(self) if x: passReturns True if x is nonzero__repr__(self) y = eval(`x`) Returns an eval()-able representation of x.Using backticks is the same as calling repr().__str__(self) print x Returns a human-readable representation of x__unicode__(self) print x Returns a human-readable Unicoderepresentation of x

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def __cmp__(self, other):return cmp(self.area(), other.area())

rectA = Rectangle(4, 4)rectB = Rectangle(8, 2)rectA == rectB # True because both have the same arearectA < rectB # False

def __cmp__(self, other):if (self.width != other.width):

return cmp(self.width, other.width)return cmp(self.height, other.height)

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def __nonzero__(self):return self.width or self.height)

def __repr__(self):return "Rectangle(%d, %d)" % (self.width, self.height)

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Method Syntax Method Syntax__float__(self)float(x) __int__(self) int(x)__abs__(self) abs(x) __neg__(self) -x__add__(self, other) x + y __sub__(self, other) x - y__iadd__(self, other) x +=y __isub__(self, other) x -= y__radd__(self, other) y + x __rsub__(self, other) y - x__mul__(self, other) x * y __mod__(self, other) x % y__imul__(self, other) x *= y __imod__(self, other) x %= y__rmul__(self, other) y * x __rmod__(self, other) y % x__floordiv__(self, other) x // y __truediv__(self, other) x / y__ifloordiv__(self, other) x //= y __itruediv__(self, other) x /= y__rfloordiv__(self, other) y // x __rtruediv__(self, other) y / x

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Static Data, and Static Methods and Decorators

class Balloon(object):unique_colors = set()def __init__(self, color):

self.color = colorBalloon.unique_colors.add(color)

@staticmethoddef uniqueColorCount():

return len(Balloon.unique_colors)@staticmethoddef uniqueColors():

return Balloon.unique_colors.copy()

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class Example: staticVariable = 5 print("starting\n")# Access through classprint (Example.staticVariable) # prints 5# Access through instanceinstance = Example()print (instance.staticVariable) # still 5

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# Change within instanceinstance.staticVariable = 6print (instance.staticVariable) # 6print (Example.staticVariable) # 5# Change through classExample.staticVariable = 7print (instance.staticVariable) # still 6print (Example.staticVariable) # now 7print("\nfinishing")

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class Example(object): name = "Example" @staticmethod def static(): print ("%s static() called" % Example.name) class Offspring1(Example): name = "Offspring1"

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class Offspring2(Example): name = "Offspring2" @staticmethod def static(): print ("%s static() called" % Example.name)print("starting\n")Example.static() # prints ExampleOffspring1.static() # prints ExampleOffspring2.static() # prints Offspring2print("\nfinishing“)

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class Example: name = "Example" @classmethod def static(cls): print ("%s static() called" % cls.name)class Offspring1(Example): name = "Offspring1" pass

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class Offspring2(Example): name = "Offspring2" @classmethod def static(cls): print ("%s static() called" % cls.name)print("starting\n")Example.static() # prints ExampleOffspring1.static() # prints Offspring1Offspring2.static() # prints Offspring2print("\nfinishing")

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Inheritance and Polymorphism

class Item(object): def __init__(self, artist, title, year=None): self.__artist = artist self.__title = title self.__year = year def artist(self): return self.__artist def setArtist(self, artist): self.__artist = artist def title(self): return self.__title

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Inheritance and Polymorphism def title(self): return self.__title def setTitle(self, title): self.__title = title def year(self): return self.__year def setYear(self, year): self.__year = year def __str__(self): year = "" if self.__year is not None: year = " in %d" % self.__year return "%s by %s%s" % (self.__title, self.__artist, year)

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class Painting(Item): def __init__(self, artist, title, year=None): super(Painting, self).__init__(artist, title, year) # item.__init__(self, artist, title, year)class Sculpture(Item): def __init__(self, artist, title, year=None, material=None): super(Sculpture, self).__init__(artist, title, year) self.__material = material

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def material(self): return self.__material def setMaterial(self, material): self.__material = material def __str__(self): materialString = "" if self.__material is not None: materialString = " (%s)" % self.__material return "%s%s" % (super(Sculpture, self).__str__(), materialString)

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class Title(object):def __init__(self, title)self.__title = titledef title(self):return self.__title return "%s%s" % (super(Sculpture, self).__str__(), materialString)

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items = []items.append(Painting("Cecil Collins", "The Poet", 1941))items.append(Sculpture("Auguste Rodin", "Naked Balzac", 1917,"plaster"))items.append(Title("Eternal Springtime"))for item in items:print item.title()

Rapid GUI Programming with Python and Qt

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