Add context manager example to user guide #1476

isosphere · 2021-03-07T17:18:47Z

A simple illustrative example on how to use context managers. I required this to use pymc3, which relies heavily on the context stack for modelling.

My example has a gap in that it calls __exit__ with blank arguments. I don't honestly know how to use it without them, or if I even need to call it at all. If anyone wants to add some detail there, I'd appreciate it!

A simple illustrative example on how to use context managers. I required this to use pymc3, which relies heavily on the context stack for modelling.

isosphere · 2021-03-07T18:03:31Z

CI failure looks unrelated:


failures:

---- types::string::test::test_extract_char stdout ----
---- types::string::test::test_extract_char stderr ----
thread 'main' panicked at 'called `Result::unwrap()` on an `Err` value: PyErr { type: <class 'ValueError'>, value: ValueError('expected a string of length 1'), traceback: None }', src/types/string.rs:239:73
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace


failures:
    types::string::test::test_extract_char

test result: FAILED. 236 passed; 1 failed; 0 ignored; 0 measured; 0 filtered out; finished in 4.32s

davidhewitt · 2021-03-07T18:25:36Z

Thanks, will read later! Yes, the coverage failure is a regression in upstream Rust nightly that'll be fixed in good time ;)

davidhewitt

Thanks very much for writing this. You're right that the __exit__ part probably needs some expansion - I've added a comment below.

guide/src/python_from_rust.md

isosphere · 2021-03-08T23:06:02Z

Thanks for your suggestion! I ran with it, and did a little eval with an undefined variable which will always throw an exception. Here's the output I get:

Welcome to 123 Main Street!
Sorry you had <class 'NameError'> trouble at 123 Main Street

Your use of py.None() there results in a moved value, so I passed it by reference (even though that branch of the match will never execute, but it should be helpful as an example of what to do).

However, I'm not certain that it's okay to pass py.None() by reference here.

davidhewitt

Thanks, just two final nits!

davidhewitt · 2021-03-09T21:39:36Z

guide/src/python_from_rust.md

+
+        "#, "objects.py", "objects").unwrap();
+
+        let house = custom_manager.call1("House", ("123 Main Street",)).unwrap();


Should be call_function1, because we actually just deprecated call1 on master.

@birkenfeld strictly speaking this isn't a function, so maybe call_attribute is better? Although I wonder if actually we should plan to remove module::call{_function} etc. completely and instead just ask users to do .getattr("...")?.call1("...")? etc? It's not much longer and doesn't suffer with naming ambiguity.

I think you must mean call_method1, so I've changed it to that!

See e065f9b - call_function1 is very hot off the press :)

Oops, you updated the documentation in that commit. Ignore earlier message if you saw it! I'll make the change!

Changes made, though I'm having trouble using that code in a little test bed I made. My cargo.toml has

[dependencies] pyo3 = {git = "https://github.com/PyO3/pyo3.git", features=["auto-initialize"]}

That change is in master, so I figure it should be active. Did a cargo clean for fun.

cargo run gives

Compiling proc-macro2 v1.0.24 Compiling unicode-xid v0.2.1 Compiling syn v1.0.62 Compiling proc-macro-hack v0.5.19 Compiling winapi v0.3.9 Compiling cfg-if v1.0.0 Compiling libc v0.2.88 Compiling unindent v0.1.7 Compiling smallvec v1.6.1 Compiling scopeguard v1.1.0 Compiling pyo3 v0.13.2 (https://github.com/PyO3/pyo3.git#b75a8f6e) Compiling instant v0.1.9 Compiling lock_api v0.4.2 Compiling quote v1.0.9 Compiling paste-impl v0.1.18 Compiling paste v0.1.18 Compiling parking_lot_core v0.8.3 Compiling parking_lot v0.11.1 Compiling pyo3-macros-backend v0.13.2 (https://github.com/PyO3/pyo3.git#b75a8f6e) Compiling indoc-impl v0.3.6 Compiling indoc v0.3.6 Compiling pyo3-macros v0.13.2 (https://github.com/PyO3/pyo3.git#b75a8f6e) Compiling pyo3-context-example v0.1.0 (C:\Users\Matt\Documents\Development\Rust\pyo3-context-example) error[E0599]: no method named `call_function0` found for reference `&PyAny` in the current scope --> src\main.rs:22:15 | 22 | house.call_function0("__enter__").unwrap(); | ^^^^^^^^^^^^^^ method not found in `&PyAny` error[E0599]: no method named `call_function1` found for reference `&PyAny` in the current scope --> src\main.rs:30:23 | 30 | house.call_function1("__exit__", (&none, &none, &none)).unwrap(); | ^^^^^^^^^^^^^^ method not found in `&PyAny` error[E0599]: no method named `call_function1` found for reference `&PyAny` in the current scope --> src\main.rs:33:23 | 33 | house.call_function1( | ^^^^^^^^^^^^^^ method not found in `&PyAny` error: aborting due to 3 previous errors For more information about this error, try `rustc --explain E0599`. error: could not compile `pyo3-context-example` To learn more, run the command again with --verbose.

I'm probably missing something?

guide/src/python_from_rust.md

davidhewitt · 2021-03-10T07:31:13Z

guide/src/python_from_rust.md

+        // If the eval threw an exception we'll pass it through to the context manager. 
+        // Otherwise, __exit__  is called with empty arguments (Python "None").


kngwyu

Simple and illustrative example 👍🏼 , thank you!

kngwyu · 2021-03-11T15:34:57Z

guide/src/python_from_rust.md

+        else:
+            print(f"Thank you for visiting {self.address}, come again soon!")
+
+        "#, "objects.py", "objects").unwrap();


Just a nit, but is house.py better?

I agree, changed!

s/objects.py/house.py/

guide/src/python_from_rust.md

birkenfeld · 2021-03-13T17:41:57Z

As for call_function vs call_method vs call: you're right, while call_function is better than call, it's not really such a good name and call_attr would be better. Or even no special API.

In the end I wish we could implement some Fn trait for PyAny which would make this much easier :)

davidhewitt · 2021-03-13T17:54:57Z

In the end I wish we could implement some Fn trait for PyAny which would make this much easier :)

I have been abstractly dreaming recently about a macro to solve all this, spread args and kwargs and also use the Vectorcall optimization. E.g.:

py_call!(module.attr(a, b, *args, **kwargs));

but that's probably a pipe dream 😄

Co-authored-by: David Hewitt <1939362+davidhewitt@users.noreply.github.com>

davidhewitt · 2021-03-13T22:54:02Z

👍 Thanks very much for this example; sorry for the complications caused by our API changes.

isosphere added 2 commits March 7, 2021 13:05

Add context manager example

924d5a1

A simple illustrative example on how to use context managers. I required this to use pymc3, which relies heavily on the context stack for modelling.

Clippy changes to context example

13d430c

davidhewitt reviewed Mar 8, 2021

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Extend context manager example with exit exceptions

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davidhewitt approved these changes Mar 9, 2021

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isosphere added 2 commits March 9, 2021 18:52

Context manager, s/call1/call_method1/ and comments for clarity

9c85db8

Add newline to context manager section to avoid horizontal scrolling

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davidhewitt reviewed Mar 10, 2021

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kngwyu approved these changes Mar 11, 2021

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isosphere added 3 commits March 11, 2021 17:52

Change generic, potentially confusing label.

55b9550

s/objects.py/house.py/

Use call_function1 rather than call_method1.

75231e4

Missed a call_method0, change to call_function0

1b4cbf0

davidhewitt reviewed Mar 13, 2021

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davidhewitt mentioned this pull request Mar 13, 2021

pymodule: remove call_function etc. #1492

Merged

isosphere and others added 2 commits March 13, 2021 14:38

Update guide/src/python_from_rust.md

69bb203

Co-authored-by: David Hewitt <1939362+davidhewitt@users.noreply.github.com>

Update guide/src/python_from_rust.md

2ff7dee

Co-authored-by: David Hewitt <1939362+davidhewitt@users.noreply.github.com>

davidhewitt merged commit e24f29d into PyO3:master Mar 13, 2021

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Add context manager example to user guide #1476

Add context manager example to user guide #1476

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birkenfeld commented Mar 13, 2021

davidhewitt commented Mar 13, 2021

davidhewitt commented Mar 13, 2021


		"#, "objects.py", "objects").unwrap();

		let house = custom_manager.call1("House", ("123 Main Street",)).unwrap();

		// If the eval threw an exception we'll pass it through to the context manager.
		// Otherwise, __exit__ is called with empty arguments (Python "None").

Add context manager example to user guide #1476

Add context manager example to user guide #1476

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