piping an email message

[Gerhard Häring]

Alessio Pace wrote:
> Hi, I am writing a filter for the emails, I need it to pass through stdin
> and then go via stdout.
> 
> Would this piece of code be okay to let just pass the message through the
> pipe correctly?
> 
> # file 'pipe.py'
> import email
> import sys
> 
> def main():
>     stdin_message = sys.stdin.read()
>     msg = email.message_from_string(stdin_message)
>     sys.stdout.write(str(msg))  
> 
> if __name__ == '__main__':
>     main()

The problem with this code is that it needs to read the entire message 
into memory. For 90 % of the messages, this should be no problem, but 
for the few multi-megabyte messages that you'll probably process, it 
will have negative impacts on the system performance.

I'd rather do something like:

#v+
CHUNK_SIZE = 1024

while True:
     chunk = sys.stdin.read(CHUNK_SIZE)
     if not chunk: break
     sys.stdout.write(chunk)
#v-

Now that you know how to do it properly, you can use the relevant 
library function in the first place :-)

#v+
import shutil
shutil.copyfileobj(sys.stdin, sys.stdout)
#v-

As you'll read strings, anyway, the explicit conversion to string using 
str() in your above code is superfluous, btw.

-- Gerhard