Intercepting stdout of a subprocess while it is running

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As Charles already mentioned, the problem is buffering. I ran in to a similar problem when writing some modules for SNMPd, and solved it by replacing stdout with an auto-flushing version.

I used the following code, inspired by some posts on ActiveState:

class FlushFile(object):
    """Write-only flushing wrapper for file-type objects."""
    def __init__(self, f):
        self.f = f
    def write(self, x):
        self.f.write(x)
        self.f.flush()

# Replace stdout with an automatically flushing version
sys.stdout = FlushFile(sys.__stdout__)

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