Can I redirect the stdout in python into some sort of string buffer?

Question

I'm using python's ftplib to write a small FTP client, but some of the functions in the package don't return string output, but print to stdout. I want to redirect stdout to an object which I'll be able to read the output from.

I know stdout can be redirected into any regular file with:

stdout = open("file", "a")

But I prefer a method that doesn't uses the local drive.

I'm looking for something like the BufferedReader in Java that can be used to wrap a buffer into a stream.

Answer 1

Use pipe() and write to the appropriate file descriptor.

http://www.python.org/doc/2.3/lib/os-fd-ops.html

Answer 2

from cStringIO import StringIO

old_stdout = sys.stdout
sys.stdout = mystdout = StringIO()

# blah blah lots of code ...

sys.stdout = old_stdout

# examine mystdout.getvalue()

Answer 3

Just to add to Ned's answer above: you can use this to redirect output to any object that implements a write(str) method.

This can be used to good effect to "catch" stdout output in a GUI application.

Here's a silly example in PyQt:

import sys
from PyQt4 import QtGui

class OutputWindow(QtGui.QPlainTextEdit):
def write(self, txt):
    self.appendPlainText(str(txt))

app = QtGui.QApplication(sys.argv)
out = OutputWindow()
sys.stdout=out
out.show()
print "hello world !"