深入浅析python with语句简介

 # 自定义支持with语句的对象 class DummyRes: def __init__(self, tag): self.tag = tag def __enter__(self): print("Enter >>> {}".format(self.tag)) return self def __exit__(self, exc_type, exc_value, exc_tb): print("Exit <<< {}".format(self.tag)) if exc_tb is None: print("Exit without Exception {}".format(self.tag)) return False else: print("Exit with Exception {}".format(self.tag)) return True # 支持closing 上下文with语句对象 class Closing: def __init__(self, thing): self.thing = thing def __enter__(self): return self def __exit__(self, exc_type, exc_value, exc_tb): self.thing.close() class ClosingDemo: def __init__(self): self.acquire() def acquire(self): print("Acquire RES") def close(self): print("Close RES") from contextlib import contextmanager class ContextDemo: def __init__(self): print("Context Demo init") raise Exception print("Context Demo init") def print(self): print("Context Demo print 1") #raise Exception print("Context Demo print 2") def close(self): print("Context Demo close") def context_demo(): print("context demo in") raise Exception print("context demo out") @contextmanager def demo(): print("Allocate Resoures") try: yield context_demo finally: print("raise exception") #yield "*** contextmanager demo ***" print("Free Resoures") if __name__ == "__main__": # 1. 使用with语句 (自动关闭文件) with open("test.txt", "w") as f: f.write("write test") # 2. 自动定义with语句 with DummyRes("test") as res: print("With body 1") raise Exception print("With body 2") # 3. 利用contextlib定义with语句 with demo(): print("exc demo") # 4. closing 上下文 (适合有close操作的情况) with Closing(ClosingDemo()): print("Use Resoures")