effectivepython/example_code/item_29.py at master · AISTLAB/effectivepython · GitHub

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#!/usr/bin/env python3

# Licensed under the Apache License, Version 2.0 (the "License");

# you may not use this file except in compliance with the License.

# You may obtain a copy of the License at

# http://www.apache.org/licenses/LICENSE-2.0

# Unless required by applicable law or agreed to in writing, software

# distributed under the License is distributed on an "AS IS" BASIS,

# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

# See the License for the specific language governing permissions and

# limitations under the License.

# Preamble to mimick book environment

import logging

from pprint import pprint

from sys import stdout as STDOUT

# Example 1

class OldResistor(object):

def __init__(self, ohms):

self._ohms = ohms

def get_ohms(self):

return self._ohms

def set_ohms(self, ohms):

self._ohms = ohms

# Example 2

r0 = OldResistor(50e3)

print('Before: %5r' % r0.get_ohms())

r0.set_ohms(10e3)

print('After: %5r' % r0.get_ohms())

# Example 3

r0.set_ohms(r0.get_ohms() + 5e3)

# Example 4

class Resistor(object):

def __init__(self, ohms):

self.ohms = ohms

self.voltage = 0

self.current = 0

r1 = Resistor(50e3)

r1.ohms = 10e3

print('%r ohms, %r volts, %r amps' %

(r1.ohms, r1.voltage, r1.current))

# Example 5

r1.ohms += 5e3

# Example 6

class VoltageResistance(Resistor):

def __init__(self, ohms):

super().__init__(ohms)

self._voltage = 0

@property

def voltage(self):

return self._voltage

@voltage.setter

def voltage(self, voltage):

self._voltage = voltage

self.current = self._voltage / self.ohms

# Example 7

r2 = VoltageResistance(1e3)

print('Before: %5r amps' % r2.current)

r2.voltage = 10

print('After: %5r amps' % r2.current)

# Example 8

class BoundedResistance(Resistor):

def __init__(self, ohms):

super().__init__(ohms)

@property

def ohms(self):

return self._ohms

@ohms.setter

def ohms(self, ohms):

if ohms <= 0:

raise ValueError('%f ohms must be > 0' % ohms)

self._ohms = ohms

# Example 9

try:

r3 = BoundedResistance(1e3)

r3.ohms = 0

except:

logging.exception('Expected')

else:

assert False

# Example 10

try:

BoundedResistance(-5)

except:

logging.exception('Expected')

else:

assert False

# Example 11

class FixedResistance(Resistor):

def __init__(self, ohms):

super().__init__(ohms)

@property

def ohms(self):

return self._ohms

@ohms.setter

def ohms(self, ohms):

if hasattr(self, '_ohms'):

raise AttributeError("Can't set attribute")

self._ohms = ohms

# Example 12

try:

r4 = FixedResistance(1e3)

r4.ohms = 2e3

except:

logging.exception('Expected')

else:

assert False

# Example 13

class MysteriousResistor(Resistor):

@property

def ohms(self):

self.voltage = self._ohms * self.current

return self._ohms

@ohms.setter

def ohms(self, ohms):

self._ohms = ohms

# Example 14

r7 = MysteriousResistor(10)

r7.current = 0.01

print('Before: %5r' % r7.voltage)

r7.ohms

print('After: %5r' % r7.voltage)

effectivepython/example_code/item_29.py at master · AISTLAB/effectivepython · GitHub

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