Python: Run Code that Prints to STDOUT or STDERR and Capture the Output into a Variable (a.k.a. output buffering to a variable)

capture_stdout_stderr.py

# derived from https://wrongsideofmemphis.wordpress.com/2010/03/01/store-standard-output-on-a-variable-in-python/

import sys
from io import StringIO
# from StringIO import StringIO # for python2

# These functions are not thread-safe and are not thread-local, it is global 
# across the entire process (all subthreads). It does not apply to child 
# processes. If during the execution of `func`, the current thread yields to 
# another thread, then you may experience both a leak of the global side-effect 
# and/or race conditions on the mutation of the stdout/stderr designators.

# Oh just discovered `contextlib.redirect_stdout` and `contextlib.redirect_stderr`
# They are available on the latest Python 3. They do the same thing, but are also 
# re-entrant.

# This means, you can reuse the same context multiple times. However these 
# functions should also be re-entrant, but each nested call will print to a new 
# buffer. There's no way to reuse the same buffer.

# The contextlib is more flexible, as you get to choose whether you want to 
# reuse the same buffer, or start a new buffer! Plus it's in the standard 
# library!

def capture_out(func):
    try:
        old_stdout = sys.stdout
        result = StringIO()
        sys.stdout = result
        func()
        result_string = result.getvalue()
        return result_string
    finally:
        sys.stdout = old_stdout
    
def capture_err(func):
    try:
        old_stderr = sys.stderr
        result = StringIO()
        sys.stderr = result
        func()
        result_string = result.getvalue()
        return result_string
    finally:
        sys.stderr = old_stderr

def capture_out_err(func):
    try:
      old_stdout = sys.stdout
      old_stderr = sys.stderr
      result_out = StringIO()
      result_err = StringIO()
      sys.stdout = result_out
      sys.stderr = result_err
      func()
      result_out_string = result_out.getvalue()
      result_err_string = result_out.getvalue()
      return (result_out_string, result_err_string)
    finally:
      sys.stdout = old_stdout
      sys.stderr = old_stderr

def capture_out_err_inter(func):
    try:
        old_stdout = sys.stdout
        old_stderr = sys.stderr
        result = StringIO()
        sys.stdout = result
        sys.stderr = result
        func()
        result_string = result.getvalue()
        return result_string
    finally:
        sys.stdout = old_stdout
        sys.stderr = old_stderr