Custom Patches

This guide will show you how to write custom patches for your own use cases.

Cillow comes with prebuilt patches to capture real-time streaming outputs generated during code execution so they can be redirected to the client when added. Currently, the following patches are available:

patch_stdout_stderr_write: Captures sys.stdout and sys.stderr writes.
patch_matplotlib_pyplot_show: Captures matplotlib.pyplot.show() calls.
patch_pillow_show: Captures PIL.Image.show() calls.

Cillow does not add the prebuilt patches by default. You need to add them explicitly. This provides more flexibility and control if you wish to process those streams in a different way.

Writing Your Own Patches¶

Any callable can be patched, whether it is a function, class, or method.

from contextlib import contextmanager
import os

import cillow

os_system_switchable = cillow.Switchable(os.system)

@contextmanager
def patch_os_system():
    def disabled_os_system(command: str):
        return "os.system has been disabled."

    with os_system_switchable.switch_to(disabled_os_system):
        yield

with patch_os_system():
    print(os.system("echo hello"))

Output

os.system has been disabled.

It is recommended to avoid fully disabling functionality, as it might be needed elsewhere for actual operations. Instead, modify the functionality based on your specific use case.

For example, if you want to disable functionality only for certain inputs, you can add conditional checks instead of disabling the entire functionality:

os_system_switchable = cillow.Switchable(os.system)

@contextmanager
def patch_os_system():
    def ignore_rm_command(command: str):
        if command.startswith("rm"):
            return "rm commands are blocked."
        return os_system_switchable.original(command)

    with os_system_switchable.switch_to(ignore_rm_command):
        yield

Important

Avoid directly invoking the patched callable within a patch function, as it can cause an infinite loop.

Instead, use the original method of the Switchable instance to access the original functionality.

Example: In the example above, we used os_system_switchable.original instead of os.system to call the original os.system function.

with patch_os_system():
    print(os.system("echo hello"))
    print(os.system("rm -rf /"))

Output

hello
0  # os.system returns 0 for successful execution
rm commands are blocked.

Refer to the Switchable component to learn how it works internally.

Adding Patches¶

cillow.add_patches(patch_os_system)

Clearing Patches¶

cillow.clear_patches()