python - python 中的 socket.gethostbyname(hostname) 有超时值吗？

Question

我在 python 中使用 socket 的 gethostbyname() 将主机名转换为 IPv4 地址。有时显示 IP 地址只需要很少的额外时间。我想知道每次查找是否有任何默认超时值。这是我在我的程序中使用套接字的方式-

try:
    addr = socket.gethostbyname(hostname)
except socket.gaierror:
    addr = "" 
print hostname+" : "+addr

只需要添加另一个问题，这是否有可能错过任何 IP 地址？任何人都有将大量主机名样本转换为 IP 地址的经验吗？

Answer 1

下面是一个使用警报信号(用于 posix 类型系统)为 socket.gethostbyname 设置超时的示例:

设置代码:

from contextlib import contextmanager
import signal

def raise_error(signum, frame):
    """This handler will raise an error inside gethostbyname"""
    raise OSError

@contextmanager
def set_signal(signum, handler):
    """Temporarily set signal"""
    old_handler = signal.getsignal(signum)
    signal.signal(signum, handler)
    try:
        yield
    finally:
        signal.signal(signum, old_handler)

@contextmanager
def set_alarm(time):
    """Temporarily set alarm"""
    signal.setitimer(signal.ITIMER_REAL, time)
    try:
        yield
    finally:
        signal.setitimer(signal.ITIMER_REAL, 0) # Disable alarm

@contextmanager
def raise_on_timeout(time):
    """This context manager will raise an OSError unless
    The with scope is exited in time."""
    with set_signal(signal.SIGALRM, raise_error):
        with set_alarm(time): 
            yield

执行代码

import socket
try:
    with raise_on_timeout(0.1): # Timeout in 100 milliseconds
        print(socket.gethostbyname(socket.gethostname()))
except OSError:
    print("Could not gethostbyname in time")