I created 2 method (first, last) and a third one (sum); I want the sum of returned value of first and last and then stored in sum; then I want to display the returned value of the sum.
P.S. I am practicing class and object. This problem can be solved using very basic syntax but I want to learn the class and objects. I am telling this cause, you may think that why am I doing this when there are easier way to do that. ;)
Thanks
class Total:
def __init__(self, x, y):
self.x = x
self.y = y
def first(self):
if self.x < 15:
return self.x * self.y
else:
return self.x - self.y
def last(self):
if self.x < 100:
return self.x + 5
else:
return self.x - 6
def sum(self):
pass
# I need help here
# add returned value of first() and last()
p = Total(25, 5)
p.sum()
You can return the first() and last() methods accumulated sum from the sum() method like:
class Total:
def __init__(self, x, y):
self.x = x
self.y = y
def first(self):
if self.x < 15:
return self.x * self.y
else:
return self.x - self.y
def last(self):
if self.x < 100:
return self.x + 5
else:
return self.x - 6
def sum(self):
return self.first() + self.last()
p = Total(25, 5)
print(p.sum())
Output:
50
Related
I'm stuck on a problem in Python... (i'm an absolute beginner but i need to do a little
environmental science model..)
so the problem is I have:
class C:
def __init__(self, x, y, z):
self.x = x
self.y = self.x * 8
self.z = self.y * 9 + 0.5
self.w = self.z +2
one = C(5,8,12)
two = C(2,12,12)
three = C(1,2,3)
So... i want to change the self.z but only for the object three
(i want it to be self.z = 12 * self.x );
I have to call it in self.w so i can't modify it after my istances...
do you have any suggestion to a beginner?
Thank you so much and have a nice day!
A few notes. First you are not actually using the arguments of y or z that are passed in __init__(self, x, y, z).
To allow on the fly overloading, you may want to break out the individual assignments into their own methods so it is easier to change the behavior you want.
Below you can pass in a custom function that will be applied to the x value when calculating z.
class C:
def __init__(self, x, custum_fn_z=None):
self.x = x
self.y = self.calc_y()
self.z = self.calc_z(custum_fn_z)
self.w = self.calc_w()
def calc_y(self):
return self.x * 8
def calc_z(self, custom_fn_z=None):
if custom_fn_z:
return custom_fn_z(self.x)
return self.y * 9 + 0.5
def calc_w(self):
return self.z +2
to use it:
one = C(5)
two = C(2)
three = C(1, lambda x: 12*x)
So the task is to make a universal Vector class to perform add method whatever(str or int) the x,y values are.
So here is the code that i've tried to execute just to check if try,except somehow works inside a class
class Vector():
def __init__(self,x,y):
self.x = x
self.y = y
def __valuecheck__(self):
try:
self.x + "a"
except TypeError:
return str(self.x)
def __add__(self, other):
return Vector(self.x + other.x, self.y + other.y)
def __repr__(self):
return "Vector({},{})".format(self.x,self.y)
a = Vector(1,"a")
b = Vector("a",2)
c = a.__add__(b)
print(c)
The expected output is
Vector(1a,a2)
I've tried different variants, defining classic function e.g. def valuecheck(), as well tried adding try,except to add and init method, but none seem to work. Need your help guys, any tip is very appreciated!
Cheers!
I think I have found the answer.
class Vector():
def __init__(self,x,y):
self.x = x
self.y = y
def __valuecheck__(self):
try:
self.x + "a"
except TypeError:
return str(self.x)
def __repr__(self):
return "Vector({},{})".format(self.x,self.y)
def __add__(self, other):
mvbh = str(self.x), str(self.y) # My Vector Before Hand
myVector = ''.join(mvbh)
ovbh = str(other.x), str(other.y) # Other Vector Before Hand
otherVector = ''.join(ovbh)
final = "Vector({}, {})".format(myVector, otherVector) # Change this to create a new vector
print(final)
a = Vector(1,"a")
b = Vector("a",2)
a.__add__(b)
class Vector():
def __init__(self,x,y):
self.x = x
self.y = y
def __valuecheck__(self):
try:
self.x + "a"
except TypeError:
return str(self.x)
def __add__(self, other):
return Vector(str(self.x) + str(other.x), str(self.y) + str(other.y))
def __repr__(self):
return "Vector({},{})".format(self.x,self.y)
a = Vector(1,"a")
b = Vector("a",2)
c = a.__add__(b)
print(c)
I would like to write a class Calculator including:
a function called add that takes two parameters containing double values and returns their sum
a function called subtract that takes two parameters containing double values and returns their difference (subtract the second from the first)
a function called multiply that takes two parameters containing double values and returns their product
a function called divide that takes two parameters containing double values and returns the value of the first divided by the second. If the second number is a zero, do not divide, and return "You can't divide by zero!"
This is my attempt, but apparently it's not correct.
class Calculator:
def add(x,y):
return x+ y
def subtract(x,y):
return x - y
def multiply(x,y):
return x * y
def divide(x,y):
if y==0:
return "You can t divide by zero!"
else:
return x/y
From the results, I get unexpected identifier x and y.
Object methods in python need to explicitly define the 'this' parameter you know from 'C', or the argument referring to the object itself. In Python it is usually called 'self'. For example:
class Calc:
def add(self,x,y): return x+y
Since all your methods do not really need self, and the calculator is more of a container of methods, you can define them as class methods, so Calc.add(3,4) works without creating an object:
class Calc:
#staticmethod
def add(x,y): return x+y
If you're new to python please note indentation is very important as well.
This answer will be accepted by the programming lab system:
class Calculator:
def add(self, x, y):
self.x = x
self.y = y
a = self.x + self.y
return a
def subtract(self, x, y):
self.x = x
self.y = y
a = self.x - self.y
return a
def multiply(self, x, y):
self.x = x
self.y = y
a = self.x * self.y
return a
def divide(self, x, y):
self.x = x
self.y = y
if (y == 0):
a = "You can't divide by zero!"
else:
a = self.x / self.y
return a
There are more simple soutions but this will be accepted by the programming lab editor. It can be a bit picky at times.
class Calculator:
def add(self,num1,num2):
print(num1+num2)
def subtract(self,num1,num2):
print(num1-num2)
def multiply(self,num1,num2):
print(num1*num2)
def divide(self,num1,num2):
print(num1 / num2)
object1 = Calculator()
object2 = Calculator()
object3 = Calculator()
object4 = Calculator()
object1.add(100,200)
object2.subtract(50,30)
object3.multiply(10,3)
object4.divide(250,5)
So I'm trying to implement a point class which creates a point and then rotate, scale and translate the point. Here's what I've currently written.
class Point:
'''
Create a Point instance from x and y.
'''
def __init__(self, x, y):
self.x = 0
self.y = 0
'''
Rotate counterclockwise, by a radians, about the origin.
'''
def rotate(self, a):
self.x0 = math.cos(this.a) * self.x - math.sin(this.a) * self.y
self.y0 = math.sin(this.a) * self.x + math.cos(this.a) * self.y
'''
Scale point by factor f, about the origin.
Exceptions
Raise Error if f is not of type float.
'''
def scale(self, f):
self.x0 = f * self.x
self.y0 = f * self.y
'''
Translate point by delta_x and delta_y.
Exceptions
Raise Error if delta_x, delta_y are not of type float.
'''
def translate(self, delta_x, delta_y):
self.x0 = self.x + delta_x
self.y0 = self.y + delta_y
'''
Round and convert to int in string form.
'''
def __str__(self):
return int(round(self.x))
Something in this code is generating an error. Now I haven't implementing error catching and I do have an error method at the top
class Error(Exception):
def __init__(self, message):
self.message = message
But how would I catch the error if a certain variable is not of type float?
Here's one of the if statements I'm using:
def __init__(self, x, y):
if not isinstance(x, float):
raise Error ("Parameter \"x\" illegal.")
self.x = x
self.y = y
if not isinstance(y, float):
raise Error ("Parameter \"y\" illegal.")
self.x = x
self.y = y
But that gets me an indentation error. So how exactly can I print out an error message that says exactly which variable is causing the problem?
If you want to raise an exception, do it in the Point's initializer:
def __init__(self, x, y):
if not isinstance(x, float) or not isinstance(y, float):
raise Error("Point's coordinates must be floats.")
self.x = x
self.y = y
Or convert the coordinates to float:
def __init__(self, x, y):
self.x = float(x)
self.y = float(y)
If the variable is not a float, you'll get a TypeError. Pretty much you can 'catch' these error like this;
try:
pass # your stuff here.
except e as TypeError:
print e # this means a type error has occurred, type is not correct.
Also, this would be worth reading for checking for correct types at the start with assert; https://wiki.python.org/moin/UsingAssertionsEffectively
I have a simple vector class that overloards several arithmetic operators:
class vec2:
x = 0.0
y = 0.0
def __add__(self,other):
self.x = other.x
self.y = other.y
def __mul__(self,scalar):
self.x *= scalar
self.y *= scalar
However, somewhere else I call the method like this:
class foo:
position = vec2()
velocity = vec2()
def update(self,dt):
self.position += self.velocity * dt;
However, once I get to the update function, the interpreter gives an error:
'tuple' object has no attribute 'x'
inside the __add__ function.
Why is "other" in __add__ passed as a tuple, and not a vec2?
The entire code is here.
Return new vectors when using __add__ and __mul__, and handle 'strange' types:
class vec2:
x = 0.0
y = 0.0
def __init__(self, x=0.0, y=0.0):
self.x, self.y = x, y
def __add__(self, other):
if not isinstance(other, self.__class__):
return NotImplemented
result = self.__class__(self.x, self.y)
result.x += other.x
result.y += other.y
return result
def __iadd__(self, other):
if not isinstance(other, self.__class__):
return NotImplemented
self.x += other.x
self.y += other.y
return self
def __mul__(self, other):
if not isinstance(other, self.__class__):
return NotImplemented
result = self.__class__(self.x, self.y)
result.x *= other.x
result.y *= other.y
return result
def __imul__(self, other):
if not isinstance(other, self.__class__):
return NotImplemented
self.x *= other.x
self.y *= other.y
return self
To modify the vectors in-place, use __iadd__ and __imul__; these still need to return the new value; this can be self.
Note that this does not handle just passing in a tuple of (x, y) coordinates. If you want to support that usecase, you need to specially handle it:
class foo:
def __init__(self, position=(0.0, 0.0), velocity=(1.0, 1.0)):
self.position = vec2()
self.velocity = vec2(*velocity)
def update(self, dt):
if isinstance(dt, tuple):
dt = vec2(*dt)
self.position += self.velocity * dt;
Note also that you should not really use class attributes for your position and velocity values; I've used instance attributes instead above, and took the opportunity to set both position and velocity to sane values.
Demo:
>>> f = foo()
>>> f.position.x, f.position.y
(0.0, 0.0)
>>> f.update((1, 2))
>>> f.position.x, f.position.y
(1.0, 2.0)