How to Capture Standard Output in Python Scripts?

Capturing Script Standard Output

In a scenario where a script performs specific tasks, such as writing data to its standard output, capturing that output can be crucial for further processing. A common approach involves attempting to store the output in a variable, as illustrated in the following example:

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

def write():
    sys.stdout.write("foobar")</code>

<code class="python"># mymodule.py
from writer import write

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

However, this approach fails to capture the script's output. An alternative solution, using a StringIO object and environment setup, successfully captures the output:

<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>

Python 3.4 Solution

For Python versions 3.4 and above, a more straightforward approach is available using the contextlib.redirect_stdout context manager:

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

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

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