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Python Classes - rob101 - Feb-05-2024
Although I've been coding with Python for a number of years now, I've never constructed a
Class before. This is my first attempt.class Resister:
def __init__(self, band1, band2, band3):
bands = {
"black": 0,
"brown": 1,
"red": 2,
"orange": 3,
"yellow": 4,
"green": 5,
"blue": 6,
"violet": 7,
"gray": 8,
"white": 9,
}
multi = {
"black": 1,
"brown": 10,
"red": 100,
"orange": 1000,
"yellow": 10 * 1000,
"green": 100 * 1000,
"blue": 1000000,
"violet": 10 * 1000000,
}
base_value = (bands[band1] * 10) + bands[band2]
self.value = base_value * multi[band3]
r1 = Resister("blue", "gray", "red")
print(r1.value)The 'subject' here is not the point (I know that there's a Python library for this kind of thing), rather is this the way to go, or is there a better way to do this?
RE: Python Classes - paul18fr - Feb-05-2024
Two possibilities (not necessary the best ones)
class Resister:
# variables (dictionaries) outside the constructor
bands = {
"black": 0,
"brown": 1,
"red": 2,
"orange": 3,
"yellow": 4,
"green": 5,
"blue": 6,
"violet": 7,
"gray": 8,
"white": 9,
}
multi = {
"black": 1,
"brown": 10,
"red": 100,
"orange": 1000,
"yellow": 10 * 1000,
"green": 100 * 1000,
"blue": 1000000,
"violet": 10 * 1000000,
}
def __init__(self, band1, band2, band3):
self.Band1 = band1
self.Band2 = band2
self.Band3 = band3
# method to calculate the value
def CalculateValue(self):
return ((self.bands[self.Band1] * 10) + self.bands[self.Band2]) * self.multi[self.Band3]
# NewObject = Resister("blue", "gray", "red")
# Value = NewObject.CalculateValue()
Value = Resister("blue", "gray", "red").CalculateValue()
print(f"R1 = {Value} ohms")
class Resister2:
@staticmethod
def CalculateValue(band1, band2, band3):
bands = {
"black": 0,
"brown": 1,
"red": 2,
"orange": 3,
"yellow": 4,
"green": 5,
"blue": 6,
"violet": 7,
"gray": 8,
"white": 9,
}
multi = {
"black": 1,
"brown": 10,
"red": 100,
"orange": 1000,
"yellow": 10 * 1000,
"green": 100 * 1000,
"blue": 1000000,
"violet": 10 * 1000000,
}
return ((bands[band1] * 10) + bands[band2]) * multi[band3]
Value2 = Resister2.CalculateValue("blue", "gray", "red")
print(f"R1 = {Value2} ohms")
RE: Python Classes - Gribouillis - Feb-05-2024
I suggest using Enum for colors and storing the bands as a tuple.
from enum import Enum, auto
from functools import cached_property
class Color(Enum):
BLACK = 0
BROWN = auto()
RED = auto()
ORANGE = auto()
YELLOW = auto()
GREEN = auto()
BLUE = auto()
VIOLET = auto()
GRAY = auto()
WHITE = auto()
@cached_property
def multiplier(self):
if self.value > Color.VIOLET.value:
raise ValueError("Invalid Color for resistor multiplier", self)
return 10**self.value
vars().update(Color.__members__)
class Resistor:
def __init__(self, band0, band1, band2):
self.band = tuple((band0, band1, band2))
def __repr__(self):
return f"Resistor{self.band!r}"
@property
def value(self):
return self.band[2].multiplier * (10 * self.band[0].value + self.band[1].value)
r = Resistor(BLUE, GRAY, RED)
print(r, r.value, r.band[1])Output:λ python paillasse/pf/resistor.py
Resistor(<Color.BLUE: 6>, <Color.GRAY: 8>, <Color.RED: 2>) 6800 Color.GRAYRE: Python Classes - snippsat - Feb-05-2024
(Feb-05-2024, 03:27 PM)rob101 Wrote: The 'subject' here is not the point (I know that there's a Python library for this kind of thing), rather is this the way to go, or is there a better way to do this?No is this not the best example of class usage as it dos one thing that a function could fine have done,and may by better in this case.
So can make example that fit better for a class,so here is there two method that can be calculated.
Also added docstring and some type hint,this will help when try to use method as will show documation in a Editor or using class from Repl.
class Resistor:
"""A class to represent a resistor and calculate its resistance based on color bands."""
# Class variables for band color codes,as they may be none changing fixed values
bands = {
"black": 0,
"brown": 1,
"red": 2,
"orange": 3,
"yellow": 4,
"green": 5,
"blue": 6,
"violet": 7,
"gray": 8,
"white": 9,
}
multipliers = {
"black": 1,
"brown": 10,
"red": 100,
"orange": 1000,
"yellow": 10 * 1000,
"green": 100 * 1000,
"blue": 1000000,
"violet": 10 * 1000000,
}
def __init__(self, band1, band2, band3):
"""Initialize the resistor with three color bands."""
self.band1 = band1
self.band2 = band2
self.band3 = band3
self.value = self.resistance()
def resistance(self) -> float:
"""Calculate and return the resistance value based on the current color bands."""
try:
base_value = (
self.bands[self.band1] * 10
) + self.bands[self.band2]
return base_value * self.multipliers[self.band3]
except KeyError as e:
raise ValueError(
f"Invalid color '{e.args[0]}' for a band."
) from None
def power_dissipation(self, voltage: float) -> float:
"""Calculate and return the power dissipation based on a given voltage."""
try:
power = (voltage**2) / self.value
return power
except ZeroDivisionError:
return "Resistance value must be greater than 0 to calculate power dissipation."
# Example usage
r1 = Resistor("blue", "gray", "red")
print(f'{r1.resistance()} Omhs')
# Calculate power dissipation for a 5V voltage
power_dissipation = r1.power_dissipation(5)
print(f"Power Dissipation: {power_dissipation} Watts")Output:6800 Omhs
Power Dissipation: 0.003676470588235294 Watts![[Image: y6kvoJ.png]](https://imagizer.imageshack.com/v2/xq70/923/y6kvoJ.png)
RE: Python Classes - rob101 - Feb-05-2024
Thank you all for the rapid and very helpful responses.
I will study what has been said here and apply what I can learn from this.