io - IPython: redirecting output of a Python script to a file (like bash >)

Question

I have a Python script that I want to run in IPython. I want to redirect (write) the output to a file, similar to:

python my_script.py > my_output.txt

How do I do this when I run the script in IPython, i.e. like execfile('my_script.py')

There is an older page describing a function that could be written to do this, but I believe that there is now a built-in way to do this that I just can't find.

Answer 1

IPython has its own context manager for capturing stdout/err, but it doesn't redirect to files, it redirects to an object:

from IPython.utils import io
with io.capture_output() as captured:
    %run my_script.py

print captured.stdout # prints stdout from your script

And this functionality is exposed in a %%capture cell-magic, as illustrated in the Cell Magics example notebook.

It's a simple context manager, so you can write your own version that would redirect to files:

class redirect_output(object):
    """context manager for reditrecting stdout/err to files"""


    def __init__(self, stdout='', stderr=''):
        self.stdout = stdout
        self.stderr = stderr

    def __enter__(self):
        self.sys_stdout = sys.stdout
        self.sys_stderr = sys.stderr

        if self.stdout:
            sys.stdout = open(self.stdout, 'w')
        if self.stderr:
            if self.stderr == self.stdout:
                sys.stderr = sys.stdout
            else:
                sys.stderr = open(self.stderr, 'w')

    def __exit__(self, exc_type, exc_value, traceback):
        sys.stdout = self.sys_stdout
        sys.stderr = self.sys_stderr

which you would invoke with:

with redirect_output("my_output.txt"):
    %run my_script.py