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item_065.py
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#!/usr/bin/env PYTHONHASHSEED=1234 python3
# Copyright 2014-2024 Brett Slatkin, Pearson Education Inc.
#
# 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.
### 책 예제에 맞는 환경 설정을 시작함
import random
random.seed(1234)
import logging
from pprint import pprint
from sys import stdout as STDOUT
# 모든 출력을 임시 디렉터리로 보냄
import atexit
import gc
import io
import os
import tempfile
TEST_DIR = tempfile.TemporaryDirectory()
atexit.register(TEST_DIR.cleanup)
# 윈도우에서 프로세스가 제대로 종료되도록 함
OLD_CWD = os.getcwd()
atexit.register(lambda: os.chdir(OLD_CWD))
os.chdir(TEST_DIR.name)
def close_open_files():
everything = gc.get_objects()
for obj in everything:
if isinstance(obj, io.IOBase):
obj.close()
atexit.register(close_open_files)
### 책 예제에 맞는 환경설정 끝
print("아이템 65")
print("Example 1")
import csv
with open("packages.csv", "w") as f:
f.write(
"""\
시드니,트럭,25
멜번,보트,6
브리즈번,비행기,12
퍼스,로드 트레인,90
아들레이드,트럭,17
"""
)
with open("packages.csv") as f:
for row in csv.reader(f):
print(row)
print("...")
print("Example 2")
class Delivery:
def __init__(self, destination, method, weight):
self.destination = destination
self.method = method
self.weight = weight
@classmethod
def from_row(cls, row):
return cls(row[0], row[1], row[2])
print("Example 3")
row1 = ["시드니", "트럭", "25"]
obj1 = Delivery.from_row(row1)
print(obj1.__dict__)
print("Example 4")
class RowMapper:
fields = () # CSV 파일의 열 순서와 일치해야 함
def __init__(self, **kwargs):
for key, value in kwargs.items():
if key not in type(self).fields:
raise TypeError(f"잘못된 필드: {key}")
setattr(self, key, value)
@classmethod
def from_row(cls, row):
if len(row) != len(cls.fields):
raise ValueError("필드 개수가 다름")
kwargs = dict(pair for pair in zip(cls.fields, row))
return cls(**kwargs)
print("Example 5")
class DeliveryMapper(RowMapper):
fields = ("destination", "method", "weight")
try:
DeliveryMapper.from_row([1, 2, 3, 4])
except ValueError as e:
assert str(e) == "필드 개수가 다름"
try:
DeliveryMapper(bad=1)
except TypeError as e:
assert str(e) == "잘못된 필드: bad"
obj2 = DeliveryMapper.from_row(row1)
assert obj2.destination == "시드니"
assert obj2.method == "트럭"
assert obj2.weight == "25"
print("Example 6")
class MovingMapper(RowMapper):
fields = ("source", "destination", "square_feet")
print("Example 7")
class BetterMovingMapper:
source = ...
destination = ...
square_feet = ...
print("Example 8")
class BetterRowMapper(RowMapper):
def __init_subclass__(cls):
fields = []
for key, value in cls.__dict__.items():
if value is Ellipsis:
fields.append(key)
cls.fields = tuple(fields)
print("Example 9")
class BetterDeliveryMapper(BetterRowMapper):
destination = ...
method = ...
weight = ...
try:
DeliveryMapper.from_row([1, 2, 3, 4])
except ValueError as e:
assert str(e) == "필드 개수가 다름"
try:
BetterDeliveryMapper(bad=1)
except TypeError as e:
assert str(e) == "잘못된 필드: bad"
obj3 = BetterDeliveryMapper.from_row(row1)
assert obj3.destination == "시드니"
assert obj3.method == "트럭"
assert obj3.weight == "25"
print("Example 10")
class ReorderedDeliveryMapper(BetterRowMapper):
method = ...
weight = ...
destination = ... # 위치를 옮김
row4 = ["로드 트레인", "90", "퍼스"] # 순서가 다름
obj4 = ReorderedDeliveryMapper.from_row(row4)
print(obj4.__dict__)
print("Example 11")
class Field:
def __init__(self):
self.internal_name = None
def __set_name__(self, owner, column_name):
self.internal_name = "_" + column_name
def __get__(self, instance, instance_type):
if instance is None:
return self
return getattr(instance, self.internal_name, "")
def __set__(self, instance, value):
adjusted_value = self.convert(value)
setattr(instance, self.internal_name, adjusted_value)
def convert(self, value):
raise NotImplementedError
print("Example 12")
class StringField(Field):
def convert(self, value):
if not isinstance(value, str):
raise ValueError
return value
class FloatField(Field):
def convert(self, value):
return float(value)
print("Example 13")
class DescriptorRowMapper(RowMapper):
def __init_subclass__(cls):
fields = []
for key, value in cls.__dict__.items():
if isinstance(value, Field): # 변경함
fields.append(key)
cls.fields = tuple(fields)
try:
DescriptorRowMapper.from_row([1, 2, 3, 4])
except ValueError as e:
assert str(e) == "필드 개수가 다름"
try:
DescriptorRowMapper(bad=1)
except TypeError as e:
assert str(e) == "잘못된 필드: bad"
print("Example 14")
class ConvertingDeliveryMapper(DescriptorRowMapper):
destination = StringField()
method = StringField()
weight = FloatField()
obj5 = ConvertingDeliveryMapper.from_row(row1)
assert obj5.destination == "시드니"
assert obj5.method == "트럭"
assert obj5.weight == 25.0 # 문자열이 아니고 숫자임
print("Example 15")
class HypotheticalWorkflow:
def start_engine(self):
pass
def release_brake(self):
pass
def run(self):
# `start_engine`을 실행한 후 `release_brake` 실행
pass
print("Example 16")
def step(func):
func._is_step = True
return func
print("Example 17")
class Workflow:
def __init_subclass__(cls):
steps = []
for key, value in cls.__dict__.items():
if callable(value) and hasattr(value, "_is_step"):
steps.append(key)
cls.steps = tuple(steps)
print("Example 18")
def run(self):
for step_name in type(self).steps:
func = getattr(self, step_name)
func()
print("Example 19")
class MyWorkflow(Workflow):
@step
def start_engine(self):
print("엔진 켜짐!")
def my_helper_function(self):
raise RuntimeError("호출해서는 안됨")
@step
def release_brake(self):
print("브레이크 풂!")
print("Example 20")
workflow = MyWorkflow()
workflow.run()
print("...")