How to Capture Output from a Python Script Using I/O Manipulation?

Capturing Output from a Script

Suppose you have a script that performs write operations using sys.stdout. An initial solution to capture the output and store it in a variable for further processing might be:

<code class="python"># writer.py
import sys

def write():
    sys.stdout.write("foobar")

# mymodule.py
from writer import write

out = write()
print(out.upper())</code>

However, this approach fails to capture the output.

One possible solution is to modify the scripts as follows:

<code class="python">import sys
from cStringIO import StringIO

# setup the environment
backup = sys.stdout

# ####
sys.stdout = StringIO()     # capture output
write()
out = sys.stdout.getvalue() # release output
# ####

sys.stdout.close()  # close the stream 
sys.stdout = backup # restore original stdout

print(out.upper())   # post processing</code>

This approach uses a buffer to capture the output stream.

Starting with Python 3.4, there is a more concise way to capture output using the contextlib.redirect_stdout context manager:

<code class="python">from contextlib import redirect_stdout
import io

f = io.StringIO()
with redirect_stdout(f):
    help(pow)
s = f.getvalue()</code>

This solution is simpler and eliminates the need for managing backups and closing the stream manually.

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