Add log_prints option to redirect print to logs

[zanieb]

Addresses the much requested log_stdout feature from v1 in v2 by adding a log_prints option. It is very hard for us to log standard output from within the run as we have no way to tell where the bytes are coming from (i.e. you cannot disable capturing per task or flow). We can, however, patch the builtin print method, allowing us to identify the flow or task run the message comes from.

This pull request introduces temporary patching of print to accomplish logging of prints from within tasks or flows. This will also apply to any functions within the scope of a task or a flow e.g. if they call into another library. If a flow or task run context is not present, we will just print as normal.

There are options at the flow, task, and settings level. Defaults for children (subflows and tasks) are pulled from the parent flow.

Closes #7117

Example

Play with the following, try None, False and True for values:

import prefect


@prefect.flow(log_prints=False)
def foo():
    print("foo")
    bar()


@prefect.task(log_prints=True)
def bar():
    print("bar")


foo()

Checklist

• This pull request references any related issue by including "closes <link to issue>"
  • If no issue exists and your change is not a small fix, please create an issue first.
• This pull request includes tests or only affects documentation.
• This pull request includes a label categorizing the change e.g. fix, feature, enhancement

Future work

We may add a log_stdout feature but it would operate at the infrastructure level where we actually have access to the full standard output stream.

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[zanieb]

Needs:

• Tests
• Link the the closed issue
• Prose documentation

[zanieb]

Nate is leading tests for this.
Will is leading documentation.

[anna-geller]

works 🎉

from prefect import flow

@flow(log_prints=True)
def hello():
    print("Greetings from Prefect! 🤗")

if __name__ == "__main__":
    hello()

from prefect import flow, task

@task(log_prints=True)
def print_sth_nice():
    print("This is nice")


@flow(log_prints=True)
def hello():
    print("Greetings from Prefect! 🤗")
    print_sth_nice()

if __name__ == "__main__":
    hello()

from prefect import flow, task

@task
def print_sth_nice():
    print("This is nice")


@flow
def hello():
    print("Greetings from Prefect! 🤗")
    print_sth_nice()

if __name__ == "__main__":
    hello()

from prefect import flow, task

@task(log_prints=False)
def print_sth_nice():
    print("This is nice")


@flow(log_prints=True)
def hello():
    print("Greetings from Prefect! 🤗")
    print_sth_nice()

if __name__ == "__main__":
    hello()

[anna-geller]

QA passes

[peytonrunyan]

😅

[peytonrunyan]

LGTM! The only thing is possibly a test explicitly for checking that the default behavior is False?

Also, TIL about the builtins module. I'd always thought "builtins" was just a colloquialism.

[tpdorsey]

LGTM. Only reviewed docs and docstrings.

[bunchesofdonald]

I like it!

[zanieb]

Thanks for the help everyone!