IOError: [Errno 32] Broken pipe: Python

Question

I have a very simple Python 3 script:

f1 = open('a.txt', 'r')
print(f1.readlines())
f2 = open('b.txt', 'r')
print(f2.readlines())
f3 = open('c.txt', 'r')
print(f3.readlines())
f4 = open('d.txt', 'r')
print(f4.readlines())
f1.close()
f2.close()
f3.close()
f4.close()

But it always says:

IOError: [Errno 32] Broken pipe

I saw on the internet all the complicated ways to fix this, but I copied this code directly, so I think that there is something wrong with the code and not Python's SIGPIPE.

I am redirecting the output, so if the above script was named "open.py", then my command to run would be:

open.py | othercommand

Answer 1

I feel obliged to point out that the method using

signal(SIGPIPE, SIG_DFL) 

is indeed dangerous (as already suggested by David Bennet in the comments) and in my case led to platform-dependent funny business when combined with multiprocessing.Manager (because the standard library relies on BrokenPipeError being raised in several places). To make a long and painful story short, this is how I fixed it:

First, you need to catch the IOError (Python 2) or BrokenPipeError (Python 3). Depending on your program you can try to exit early at that point or just ignore the exception:

from errno import EPIPE

try:
    broken_pipe_exception = BrokenPipeError
except NameError:  # Python 2
    broken_pipe_exception = IOError

try:
    YOUR CODE GOES HERE
except broken_pipe_exception as exc:
    if broken_pipe_exception == IOError:
        if exc.errno != EPIPE:
            raise

However, this isn't enough. Python 3 may still print a message like this:

Exception ignored in: <_io.TextIOWrapper name='<stdout>' mode='w' encoding='UTF-8'>
BrokenPipeError: [Errno 32] Broken pipe

Unfortunately getting rid of that message is not straightforward, but I finally found http://bugs.python.org/issue11380 where Robert Collins suggests this workaround that I turned into a decorator you can wrap your main function with (yes, that's some crazy indentation):

from functools import wraps
from sys import exit, stderr, stdout
from traceback import print_exc


def suppress_broken_pipe_msg(f):
    @wraps(f)
    def wrapper(*args, **kwargs):
        try:
            return f(*args, **kwargs)
        except SystemExit:
            raise
        except:
            print_exc()
            exit(1)
        finally:
            try:
                stdout.flush()
            finally:
                try:
                    stdout.close()
                finally:
                    try:
                        stderr.flush()
                    finally:
                        stderr.close()
    return wrapper


@suppress_broken_pipe_msg
def main():
    YOUR CODE GOES HERE

Answer 2

This can also occur if the read end of the output from your script dies prematurely

ie open.py | otherCommand

if otherCommand exits and open.py tries to write to stdout

I had a bad gawk script that did this lovely to me.