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ch06
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‎ch06/decorators/decorators.factory.py

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# decorators/decorators.factory.py
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from functools import wraps
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def max_result(threshold):
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def decorator(func):
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@wraps(func)
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def wrapper(*args, **kwargs):
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result = func(*args, **kwargs)
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if result > threshold:
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print(
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f'Result is too big ({result}). '
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f'Max allowed is {threshold}.'
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)
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return result
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return wrapper
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return decorator
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@max_result(75)
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def cube(n):
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return n ** 3
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@max_result(100)
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def square(n):
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return n ** 2
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@max_result(1000)
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def multiply(a, b):
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return a * b
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print(cube(5))
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"""
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$ python decorators.factory.py
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Result is too big (125). Max allowed is 75.
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125
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"""

‎ch06/decorators/syntax.py

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# decorators/syntax.py
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# This is not a valid Python module - Don't run it.
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# ONE DECORATOR
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def func(arg1, arg2, ...):
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pass
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func = decorator(func)
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# is equivalent to the following:
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@decorator
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def func(arg1, arg2, ...):
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pass
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# TWO DECORATORS
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def func(arg1, arg2, ...):
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pass
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func = deco1(deco2(func))
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# is equivalent to the following:
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@deco1
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@deco2
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def func(arg1, arg2, ...):
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pass
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# DECORATOR WITH ARGUMENTS
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def func(arg1, arg2, ...):
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pass
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func = decoarg(arg_a, arg_b)(func)
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# is equivalent to the following:
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@decoarg(arg_a, arg_b)
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def func(arg1, arg2, ...):
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pass

‎ch06/decorators/time.measure.arguments.py

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# decorators/time.measure.arguments.py
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from time import sleep, time
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def f(sleep_time=0.1):
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sleep(sleep_time)
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def measure(func, *args, **kwargs):
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t = time()
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func(*args, **kwargs)
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print(func.__name__, 'took:', time() - t)
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measure(f, sleep_time=0.3) # f took: 0.30056095123291016
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measure(f, 0.2) # f took: 0.2033553123474121

‎ch06/decorators/time.measure.deco1.py

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# decorators/time.measure.deco1.py
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from time import sleep, time
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def f(sleep_time=0.1):
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sleep(sleep_time)
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def measure(func):
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def wrapper(*args, **kwargs):
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t = time()
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func(*args, **kwargs)
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print(func.__name__, 'took:', time() - t)
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return wrapper
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f = measure(f) # decoration point
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f(0.2) # f took: 0.20372915267944336
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f(sleep_time=0.3) # f took: 0.30455899238586426
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print(f.__name__) # wrapper <- ouch!

‎ch06/decorators/time.measure.deco2.py

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# decorators/time.measure.deco2.py
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from time import sleep, time
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from functools import wraps
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def measure(func):
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@wraps(func)
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def wrapper(*args, **kwargs):
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t = time()
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func(*args, **kwargs)
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print(func.__name__, 'took:', time() - t)
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return wrapper
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@measure
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def f(sleep_time=0.1):
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"""I'm a cat. I love to sleep! """
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sleep(sleep_time)
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f(sleep_time=0.3) # f took: 0.3010902404785156
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print(f.__name__, ':', f.__doc__) # f : I'm a cat. I love to sleep!

‎ch06/decorators/time.measure.dry.py

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# decorators/time.measure.dry.py
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from time import sleep, time
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def f():
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sleep(.3)
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def g():
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sleep(.5)
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def measure(func):
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t = time()
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func()
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print(func.__name__, 'took:', time() - t)
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measure(f) # f took: 0.30434322357177734
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measure(g) # g took: 0.5048270225524902

‎ch06/decorators/time.measure.start.py

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# decorators/time.measure.start.py
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from time import sleep, time
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def f():
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sleep(.3)
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def g():
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sleep(.5)
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t = time()
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f()
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print('f took:', time() - t) # f took: 0.3001396656036377
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t = time()
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g()
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print('g took:', time() - t) # g took: 0.5039339065551758

‎ch06/decorators/two.decorators.py

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# decorators/two.decorators.py
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from time import time
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from functools import wraps
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def measure(func):
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@wraps(func)
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def wrapper(*args, **kwargs):
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t = time()
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result = func(*args, **kwargs)
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print(func.__name__, 'took:', time() - t)
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return result
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return wrapper
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def max_result(func):
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@wraps(func)
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def wrapper(*args, **kwargs):
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result = func(*args, **kwargs)
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if result > 100:
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print(
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f'Result is too big ({result}). '
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'Max allowed is 100.'
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)
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return result
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return wrapper
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@measure
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@max_result
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def cube(n):
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return n ** 3
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print(cube(2))
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print(cube(5))
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"""
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$ python two.decorators.py
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cube took: 3.0994415283203125e-06
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8
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Result is too big (125). Max allowed is 100.
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cube took: 5.9604644775390625e-06
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125
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"""

‎ch06/iterators/iterator.py

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# iterators/iterator.py
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class OddEven:
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def __init__(self, data):
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self._data = data
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self.indexes = (list(range(0, len(data), 2)) +
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list(range(1, len(data), 2)))
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def __iter__(self):
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return self
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def __next__(self):
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if self.indexes:
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return self._data[self.indexes.pop(0)]
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raise StopIteration
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oddeven = OddEven('ThIsIsCoOl!')
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print(''.join(c for c in oddeven)) # TIICO!hssol
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oddeven = OddEven('CiAo') # or manually...
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it = iter(oddeven) # this calls oddeven.__iter__ internally
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print(next(it)) # C
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print(next(it)) # A
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print(next(it)) # i
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print(next(it)) # o
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# make sure it works correctly with edge cases
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oddeven = OddEven('')
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print(' '.join(c for c in oddeven))
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oddeven = OddEven('A')
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print(' '.join(c for c in oddeven))
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oddeven = OddEven('Ab')
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print(' '.join(c for c in oddeven))
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oddeven = OddEven('AbC')
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print(' '.join(c for c in oddeven))
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"""
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$ python iterators/iterator.py
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TIICO!hssol
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C
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A
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i
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o
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A
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A b
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A C b
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"""

‎ch06/oop/cached.property.py

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# oop/cached.property.py
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from functools import cached_property
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class Client:
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def __init__(self):
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print("Setting up the client...")
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def query(self, **kwargs):
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print(f"Performing a query: {kwargs}")
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class Manager:
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@property
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def client(self):
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return Client()
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def perform_query(self, **kwargs):
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return self.client.query(**kwargs)
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class ManualCacheManager:
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@property
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def client(self):
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if not hasattr(self, '_client'):
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self._client = Client()
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return self._client
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def perform_query(self, **kwargs):
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return self.client.query(**kwargs)
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class CachedPropertyManager:
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@cached_property
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def client(self):
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return Client()
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def perform_query(self, **kwargs):
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return self.client.query(**kwargs)
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manager = CachedPropertyManager()
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manager.perform_query(object_id=42)
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manager.perform_query(name_ilike='%Python%')
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del manager.client # This causes a new Client on next call
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manager.perform_query(age_gte=18)
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"""
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$ python cached.property.py
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Setting up the client... # New Client
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Performing a query: {'object_id': 42} # first query
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Performing a query: {'name_ilike': '%Python%'} # second query
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Setting up the client... # Another Client
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Performing a query: {'age_gte': 18} # Third query
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"""

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