Python file.read（）回调

Question

I currently have code that reads raw content from a file chosen by the user:

def choosefile():
    filec = tkFileDialog.askopenfile()
    # Wait a few to prevent attempting to displayng the file's contents before the entire file was read.
    time.sleep(1)
    filecontents = filec.read()

But, sometimes people open big files that take more than 2 seconds to open. Is there a callback for FileObject.read([size]) ? For people who don't know what a callback is, it's a operation executed once another operation has executed.

Answer 1

Slightly modified from the docs:

#!/usr/bin/env python

import signal, sys

def handler(signum, frame):
    print "You took too long"
    sys.exit(1)

f = open(sys.argv[1])

# Set the signal handler and a 2-second alarm
signal.signal(signal.SIGALRM, handler)
signal.alarm(2)

contents = f.read()

signal.alarm(0) # Disable the alarm

print contents

Answer 2

Answer resolved by asker

Hm, I made a mistake at first. tkFileDialog.askopenfile() does not read the file, but FileObject.read() reads the file, and blocks the code . I found the solution according to @kindall . I'm not a complete expert at Python, though.

Your question seems to assume that Python will somehow start reading your file while some other code executes, and therefore you need to wait for the read to catch up. This is not even slightly true; both open() and read() are blocking calls and will not return until the operation has completed. Your sleep() is not necessary and neither is your proposed workaround. Simply open the file and read it. Python won't do anything else while that is happening.

Thanks kindall! Resolved code:

def choosefile():
filec = tkFileDialog.askopenfile()
filecontents = filec.read()