#!/usr/bin/env python3.7
"""
Mastering Object-Oriented Python 2e
Code Examples for Mastering Object-Oriented Python 2nd Edition
Chapter 3. Example 5.
"""
from typing import Iterable, cast, Any, Union, Type, Tuple
import random
from collections import defaultdict
from Chapter_3.ch03_ex1 import card2, Suit, Card2, AceCard2, FaceCard2, NumberCard2
from Chapter_3.ch03_ex3 import Hand, FrozenHand
# Immutable init and __new__()
# ========================================
# Doesn't work. Can't use this form of __init__ with immutable classes.
class Float_Fail(float):
def __init__(self, value: float, unit: str) -> None:
super().__init__(value)
self.unit = unit
test_float_fail = """
>>> x = Float_Fail(6.8, "knots") # doctest: +IGNORE_EXCEPTION_DETAIL
Traceback (most recent call last):
File "/Users/slott/miniconda3/envs/py37/lib/python3.7/doctest.py", line 1329, in __run
compileflags, 1), test.globs)
File "<doctest __main__.__test__.test_float_fail[0]>", line 1, in <module>
x = Float_Fail(6.8, "knots")
TypeError: float expected at most 1 arguments, got 2
"""
# This is how we can tweak an immutable object before the __init__ is invoked.
# See https://github.com/python/mypy/issues/1053
# This *should* work since v0.3.1
# Adding type hints will report mypy errors.
# float is (implicitly) a subclass of object.
# object.__new__() takes no arguments.
# float.__new__() is *really* more like type.__new__
class Float_Units(float):
def __new__(cls, value, unit):
obj = super().__new__(cls, float(value))
obj.unit = unit
return obj
test_float_units = """
>>> speed = Float_Units(6.8, "knots")
>>> speed*2
13.6
>>> speed.unit
'knots'
"""
# Option 2...
# A number of casts to work with mypy.
# While this "works" the cast(type, super() doesn't make sense.
from typing import overload, Optional, SupportsFloat, Dict
class Float_Units_Ugly(float):
unit: str
def __new__(cls: Type, value: SupportsFloat, unit: str) -> "Float_Units_Ugly":
# print(f"Float_Units_Ugly {cls}")
obj = cast("Float_Units_Ugly", cast(type, super()).__new__(cls, float(value)))
obj.unit = unit
return obj
test_float_units = """
>>> speed = Float_Units_Ugly(6.8, "knots")
>>> speed*2
13.6
>>> speed.unit
'knots'
"""
# Option 3...
# Metaclass to adjust structure.
# Also relevant to the more complex example that follows.
class AddUnitMeta(type):
def __new__(
cls: Type, name: str, bases: Tuple[Type, ...], namespace: Dict[str, Any], **kwds
) -> "Float_Units2":
namespace["unit"] = None
result = cast("Float_Units2", super().__new__(cls, name, bases, namespace))
return result
class Float_Units2(float, metaclass=AddUnitMeta):
def withUnit(self, unit):
self.unit = unit
return self
test_float_units_2 = """
>>> speed = Float_Units2(6.8).withUnit("knots")
>>> speed*2
13.6
>>> speed.unit
'knots'
"""
# Metaclass and __new__()
# ===================================
# Example 1. Classes with pre-built loggers.
import logging
class LoggedMeta(type):
def __new__(
cls: Type, name: str, bases: Tuple[Type, ...], namespace: Dict[str, Any]
) -> "Logged":
result = cast("Logged", super().__new__(cls, name, bases, namespace))
result.logger = logging.getLogger(name)
return result
class Logged(metaclass=LoggedMeta):
logger: logging.Logger
class SomeApplicationClass(Logged):
def __init__(self, v1: int, v2: int) -> None:
self.logger.info("v1=%r, v2=%r", v1, v2)
self.v1 = v1
self.v2 = v2
self.v3 = v1 * v2
self.logger.info("product=%r", self.v3)
test_meta = """
>>> import sys
>>> logging.basicConfig(stream=sys.stdout, level=logging.INFO)
>>> sa = SomeApplicationClass(6, 7)
INFO:SomeApplicationClass:v1=6, v2=7
INFO:SomeApplicationClass:product=42
>>> logging.shutdown()
"""
__test__ = {
name: value for name, value in locals().items() if name.startswith("test_")
}
if __name__ == "__main__":
import doctest
doctest.testmod(verbose=False)
