How do you read from stdin in python from a pipe which has no ending

I've problem to read from Standard input or pipe in python when the pipe is from a "open" (do not know right name) file.

I have as example pipetest.py:

import sys
import time
k = 0
try:
   for line in sys.stdin:
      k = k + 1
      print line
except KeyboardInterrupt:
   sys.stdout.flush()
   pass
print k

I run开发者_如何学Python a program that have continues output and Ctrl+c after a while

$ ping 127.0.0.1 | python pipetest.py
^C0

I get no output. But if I go via an ordinary file it works.

$ ping 127.0.0.1 > testfile.txt

this is ended by Ctrl+c after a short while

$ cat testfile.txt |  python pipetest.py

PING 127.0.0.1 (127.0.0.1) 56(84) bytes of data.
64 bytes from 127.0.0.1: icmp_seq=1 ttl=64 time=0.017 ms
64 bytes from 127.0.0.1: icmp_seq=2 ttl=64 time=0.015 ms
64 bytes from 127.0.0.1: icmp_seq=3 ttl=64 time=0.014 ms
64 bytes from 127.0.0.1: icmp_seq=4 ttl=64 time=0.013 ms
64 bytes from 127.0.0.1: icmp_seq=5 ttl=64 time=0.012 ms

--- 127.0.0.1 ping statistics ---
5 packets transmitted, 5 received, 0% packet loss, time 3998ms
rtt min/avg/max/mdev = 0.012/0.014/0.017/0.003 ms
10

How do I do to get any output before the program ends, in this case ping has ended?

Try this:

import sys
import time
k = 0
try:
    buff = ''
    while True:
        buff += sys.stdin.read(1)
        if buff.endswith('\n'):
            print buff[:-1]
            buff = ''
            k = k + 1
except KeyboardInterrupt:
   sys.stdout.flush()
   pass
print k

For this to work without waiting until the stdin stream ends, you can iter on the readline. I think this is the simplest solution.

import sys
k = 0
try:
   for line in iter(sys.stdin.readline, b''):
      k = k + 1
      print line
except KeyboardInterrupt:
   sys.stdout.flush()
   pass
print k

k = 0
try:
    while True:
        print sys.stdin.readline()
        k += 1
except KeyboardInterrupt:
    sys.stdout.flush()
    pass
print k

This is how I ended up doing this. I didn't really like any of the other solutions, they didn't seem very pythonic.

This will make a container for any open file input to iterate over all the lines. This will also take care of closing the file at the end of the context manager.

I feel like this is probably how the for line in sys.stdin: block should operate by default.

class FileInput(object):                                                        
    def __init__(self, file):                                                   
        self.file = file                                                       

    def __enter__(self):                                                        
        return self                                                             

    def __exit__(self, *args, **kwargs):                                        
        self.file.close()                                                       

    def __iter__(self):                                                         
        return self                                                             

    def next(self):                                                             
        line = self.file.readline()                                             

        if line == None or line == "":                                          
            raise StopIteration                                                 

        return line  

with FileInput(sys.stdin) as f:
    for line in f:
        print f

with FileInput(open('tmpfile') as f:
    for line in f:
        print f

From the command line both of the following should work:

tail -f /var/log/debug.log | python fileinput.py
cat /var/log/debug.log | python fileinput.py

while sys.stdin is a file-like object, meaning you can iterate over its lines, it will block until a EOF is inserted.

The behaviour can be described with the following pseudo-code:

while True:
    input = ""
    c = stdin.read(1)
    while c is not EOF:
        input += c
        c = stdin.read(1)
    for line in input.split('\n'):
        yield line

this means that, while you can iterate over sys.stdin's lines, you cannot use this approach for the task at hand and you must explicitly call read() or readline()