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danben
danben

Reputation: 83250

Capturing stdout within the same process in Python

I've got a python script that calls a bunch of functions, each of which writes output to stdout. Sometimes when I run it, I'd like to send the output in an e-mail (along with a generated file). I'd like to know how I can capture the output in memory so I can use the email module to build the e-mail.

My ideas so far were:

Upvotes: 7

Views: 6179

Answers (4)

Alex Hall
Alex Hall

Reputation: 36023

And I modified Gary Robinson's answer to make sure that stdout is always restored, even if there's an exception:

import sys, StringIO, contextlib

class Data(object):
    pass

@contextlib.contextmanager
def capture_stdout():
    old = sys.stdout
    capturer = StringIO.StringIO()
    data = Data()
    try:
        sys.stdout = capturer
        yield data
    finally:
        sys.stdout = old
        data.result = capturer.getvalue()

Upvotes: 3

Gary Robinson
Gary Robinson

Reputation: 141

I modified None's answer to make it a context manager:

import sys, StringIO, contextlib

class Data(object):
    pass

@contextlib.contextmanager
def capture_stdout():
    old = sys.stdout
    capturer = StringIO.StringIO()
    sys.stdout = capturer
    data = Data()
    yield data
    sys.stdout = old
    data.result = capturer.getvalue()

Usage:

with capture_stdout() as capture:
    print 'Hello'
    print 'Goodbye'
assert capture.result == 'Hello\nGoodbye\n'

Upvotes: 14

None
None

Reputation: 3933

It's pretty simple to capture output.

import sys, StringIO
old_stdout = sys.stdout
capturer = StringIO.StringIO()
sys.stdout = capturer
#call functions
print "Hi"
#end functions
sys.stdout = old_stdout
output = capturer.getvalue()

Upvotes: 8

Noufal Ibrahim
Noufal Ibrahim

Reputation: 72755

You said that your script "calls a bunch of functions" so I'm assuming that they're python functions accessible from your program. I'm also assuming you're using print to generate the output in all these functions. If that's the case, you can just replace sys.stdout with a StringIO.StringIO which will intercept all the stuff you're writing. Then you can finally call the .getValue method on your StringIO to get everything that has been sent to the output channel. This will also work for external programs using the subprocess module which write to sys.stdout.

This is a cheap way. I'd recommend that you do your output using the logging module. You'll have much more control over how it does it's output and you can control it more easily as well.

Upvotes: 4

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