[Python Cheatsheet] 32. contextlib 심화 - suppress, redirect, ExitStack

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from contextlib import (
    suppress,           # 예외 무시
    redirect_stdout,    # stdout 리다이렉트
    redirect_stderr,    # stderr 리다이렉트
    ExitStack,          # 동적 컨텍스트 스택
    nullcontext,        # 아무것도 안 하는 컨텍스트
    closing,            # close() 자동 호출
    asynccontextmanager # async 컨텍스트 매니저
)

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from contextlib import suppress
import os

# 파일 삭제 시 없어도 무시
with suppress(FileNotFoundError):
    os.remove('nonexistent_file.txt')
# 예외 없이 통과

# 여러 예외 타입
with suppress(FileNotFoundError, PermissionError):
    os.remove('some_file.txt')

# 동등한 코드 (suppress 없이)
try:
    os.remove('nonexistent_file.txt')
except FileNotFoundError:
    pass

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from contextlib import redirect_stdout
from io import StringIO

# 출력을 문자열로 캡처
f = StringIO()
with redirect_stdout(f):
    print("Hello, World!")
    print("This is captured")

output = f.getvalue()
print(f"Captured: {output!r}")
# Captured: 'Hello, World!\nThis is captured\n'

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from contextlib import redirect_stderr
from io import StringIO
import sys

f = StringIO()
with redirect_stderr(f):
    print("Error message", file=sys.stderr)

error_output = f.getvalue()

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from contextlib import redirect_stdout

with open('output.log', 'w') as f:
    with redirect_stdout(f):
        print("This goes to file")
        help(str)  # help 출력도 파일로

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from contextlib import ExitStack

# 동적 개수의 파일 열기
filenames = ['file1.txt', 'file2.txt', 'file3.txt']

with ExitStack() as stack:
    files = [
        stack.enter_context(open(fname, 'w'))
        for fname in filenames
    ]
    # 모든 파일에 쓰기
    for f in files:
        f.write("content")
# ExitStack이 모든 파일을 자동으로 닫음

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from contextlib import ExitStack

def cleanup(name):
    print(f"Cleaning up: {name}")

with ExitStack() as stack:
    stack.callback(cleanup, "resource1")
    stack.callback(cleanup, "resource2")
    print("Working...")
# 출력:
# Working...
# Cleaning up: resource2
# Cleaning up: resource1
# (LIFO 순서로 호출)

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from contextlib import ExitStack

def acquire_resource(name):
    print(f"Acquiring {name}")
    if name == "bad":
        raise ValueError("Failed!")
    return name

with ExitStack() as stack:
    try:
        r1 = acquire_resource("good1")
        stack.callback(print, f"Releasing {r1}")
        
        r2 = acquire_resource("bad")  # 예외 발생
        stack.callback(print, f"Releasing {r2}")
    except ValueError:
        print("Error occurred")

# 출력:
# Acquiring good1
# Acquiring bad
# Error occurred
# Releasing good1

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from contextlib import nullcontext

def process(data, lock=None):
    # lock이 있으면 사용, 없으면 무시
    with lock if lock else nullcontext():
        print(f"Processing {data}")

# lock 없이
process("data1")

# lock과 함께
import threading
my_lock = threading.Lock()
process("data2", lock=my_lock)

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from contextlib import nullcontext

# 조건부로 파일 또는 stdout
def write_output(data, filename=None):
    cm = open(filename, 'w') if filename else nullcontext(sys.stdout)
    with cm as f:
        f.write(data)

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from contextlib import closing
from urllib.request import urlopen

# urlopen은 컨텍스트 매니저가 아닌 버전 대응
with closing(urlopen('https://example.com')) as page:
    content = page.read()

# 커스텀 객체에도 사용
class Resource:
    def close(self):
        print("Resource closed")

with closing(Resource()) as r:
    print("Using resource")
# Resource closed

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from contextlib import ExitStack

class ResourceManager:
    def __init__(self):
        self._stack = ExitStack()
    
    def __enter__(self):
        return self
    
    def __exit__(self, *exc_info):
        return self._stack.__exit__(*exc_info)
    
    def add_file(self, path, mode='r'):
        f = self._stack.enter_context(open(path, mode))
        return f

with ResourceManager() as rm:
    f1 = rm.add_file('file1.txt', 'w')
    f2 = rm.add_file('file2.txt', 'w')
    f1.write("content1")
    f2.write("content2")
# 모든 파일 자동 닫힘

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from contextlib import suppress

# 나쁨 - 모든 예외 무시
with suppress(Exception):
    risky_operation()

# 좋음 - 특정 예외만 무시
with suppress(FileNotFoundError):
    os.remove('temp.txt')

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from contextlib import redirect_stdout
from io import StringIO

# 주의: redirect 블록 안에서 원래 stdout 사용 불가
original_stdout = sys.stdout

f = StringIO()
with redirect_stdout(f):
    print("Captured")
    # 원래 stdout으로 출력하려면:
    print("Direct", file=original_stdout)