# Pyffi - Use Python from Racket **URL:** \ **Category:** Show & Tell\ **Created:** [October 9, 2022, 5:51pm UTC](https://racket.discourse.group/t/pyffi-use-python-from-racket/1362 "2022-10-09T17:51:51Z")\ **Posts on this page:** 16\ **Page:** 2
**Author:** ![saludes](https://yyz2.discourse-cdn.com/free1/user_avatar/racket.discourse.group/saludes/32/831_2.png) [@saludes](https://racket.discourse.group/u/saludes)\ **Post date:** [November 15, 2022, 8:01am UTC](https://racket.discourse.group/t/pyffi-use-python-from-racket/1362/21 "2022-11-15T08:01:36Z")
Ran diagnostics: > open-input-file: cannot open module file > module path: pyffi/configure-pyffi > path: /Users/saludes/pyffi/configure-pyffi.rkt > system error: no such file or directory; rkt\_err=3 I have `pyffi` cloned into **/Users/saludes/** but **configure-pyffi.rkt** is at **pyffi-lib/pyffi/configure-pyffi.rkt** inside the cloned repo; So I guess it should be: **/Users/saludes/pyffi/pyffi-lib/pyffi/configure-pyffi.rkt** in my case. ---
**Author:** ![gus-massa](https://yyz2.discourse-cdn.com/free1/user_avatar/racket.discourse.group/gus-massa/32/507_2.png) [@gus-massa](https://racket.discourse.group/u/gus-massa)\ **Post date:** [November 15, 2022, 2:27pm UTC](https://racket.discourse.group/t/pyffi-use-python-from-racket/1362/22 "2022-11-15T14:27:01Z")
Is Python only necessary to build some examples in the docs? How difficult is to make those examples generate some comment explaining that Python is not available? Another possibility is that the examples save the results of the Python code to a .txt file that is committed to the repository along the docs, and is used in case Python is not available. Racket has a few of these pregenerated files, mostly to break cycles where the compiler would need a working copy of racket to bootstrap. ---
**Author:** ![samth](https://yyz2.discourse-cdn.com/free1/user_avatar/racket.discourse.group/samth/32/3_2.png) [@samth](https://racket.discourse.group/u/samth)\ **Post date:** [November 15, 2022, 3:40pm UTC](https://racket.discourse.group/t/pyffi-use-python-from-racket/1362/23 "2022-11-15T15:40:00Z")
Note that the `make-log-based-eval` evaluator is useful for doing exactly this. ---
**Author:** ![soegaard](https://yyz2.discourse-cdn.com/free1/user_avatar/racket.discourse.group/soegaard/32/19_2.png) [@soegaard](https://racket.discourse.group/u/soegaard)\ **Post date:** [November 15, 2022, 4:30pm UTC](https://racket.discourse.group/t/pyffi-use-python-from-racket/1362/24 "2022-11-15T16:30:20Z")
That looks promising indeed. I'll try it out. ---
**Author:** ![soegaard](https://yyz2.discourse-cdn.com/free1/user_avatar/racket.discourse.group/soegaard/32/19_2.png) [@soegaard](https://racket.discourse.group/u/soegaard)\ **Post date:** [November 15, 2022, 9:08pm UTC](https://racket.discourse.group/t/pyffi-use-python-from-racket/1362/25 "2022-11-15T21:08:10Z")
@samth Today I tried to use `make-log-based-eval` rather than the normal `make-base-eval`. The logging version logs the result of an evaluation: it write the serialized value to a file. When replayed the value is deserialized from disk. Sounds easy enough, so I added the property `prop:serializable` to the `obj` struct. The `obj` struct represents a Python object and consist of the name of the object class and a C-pointer to the Python object. Serializing the name only gets me to this result (using replay): ![image](https://global.discourse-cdn.com/free1/uploads/racket/original/1X/5841bb565fb067dc851cfd1014b1367473f8fa5e.png) Compare this to the original: ![image](https://global.discourse-cdn.com/free1/uploads/racket/original/1X/628abc9818c021feeb56faf403991e32d430ecc9.png) The missing part is stored in the Python object. Now Python also have (de)serialization called pickling and unpickling. But ... that can't be used, since the reason we are doing this is to build the documentation on a machine without Python. The idea of logging the evaluation results are good, but the logging happens too early. What is needed is a logging version of `examples` where the scribble structures is logged. At least I think so - but maybe I am missing an alternative solution? ---
**Author:** ![samth](https://yyz2.discourse-cdn.com/free1/user_avatar/racket.discourse.group/samth/32/3_2.png) [@samth](https://racket.discourse.group/u/samth)\ **Post date:** [November 15, 2022, 9:40pm UTC](https://racket.discourse.group/t/pyffi-use-python-from-racket/1362/26 "2022-11-15T21:40:31Z")
I think you would either need to have a different version of `run` that produced the full printout, or a different version of `make-log-based-evaluator` that did the printing a logging time. ---
**Author:** ![soegaard](https://yyz2.discourse-cdn.com/free1/user_avatar/racket.discourse.group/soegaard/32/19_2.png) [@soegaard](https://racket.discourse.group/u/soegaard)\ **Post date:** [November 16, 2022, 6:03pm UTC](https://racket.discourse.group/t/pyffi-use-python-from-racket/1362/27 "2022-11-16T18:03:31Z")
> I think you would either need to have a different version of `run` that produced the full printout, or a different version of `make-log-based-evaluator` that did the printing a logging time. The function `run` is just one of many functions exported by `pyffi`, so I have looked at the other option. Given an evaluator returned from `make-log-based-evaluator` the function `wrap` below will do the printing at evaluation time. Combined with `make-log-based-evaluator` I can record and replay the evaluations. However, the `examples` form doesn't know, that the values it receives have been pretty printed already. The `wrap` function was tricky. The `examples` form calls the evaluator multiple times for each example. Besides the value(s) of each example expression, it also needs to know about any activity on output and debug ports. This is done by sending "evaluator messages", but `evaluator-message?` is not exported from `racket/sandbox`. ```scheme @(require racket/match rackunit) @(require/expose racket/sandbox (evaluator-message?)) @(define (wrap ev) (lambda (x) (call-with-values (λ () (if (evaluator-message? x) (ev x) (match x ; these non-expressions are used in the manual [(cons (or 'require 'define 'import) _) (ev x)] [else (ev `(with-output-to-string (λ () (print ,x))))]))) (λ vs (apply values vs))))) ``` Example output: ![image](https://global.discourse-cdn.com/free1/uploads/racket/original/1X/a20252b8c78d678a0b0158d84f8082baff4e54c9.png) How do I get `examples` to format these pretty printed values correctly? ---
**Author:** ![samth](https://yyz2.discourse-cdn.com/free1/user_avatar/racket.discourse.group/samth/32/3_2.png) [@samth](https://racket.discourse.group/u/samth)\ **Post date:** [November 16, 2022, 6:43pm UTC](https://racket.discourse.group/t/pyffi-use-python-from-racket/1362/28 "2022-11-16T18:43:40Z")
I think that instead of producing a string directly, you need to produce something whose printed representation is that string. Maybe like (totally untested and buggy): ```scheme (struct v (s) #:property prop:custom-write (lambda (v p m) (write (v-s v) p)) ``` and then wrap `(v ...)` around the `with-output-to-string`. ---
**Author:** ![soegaard](https://yyz2.discourse-cdn.com/free1/user_avatar/racket.discourse.group/soegaard/32/19_2.png) [@soegaard](https://racket.discourse.group/u/soegaard)\ **Post date:** [November 18, 2022, 2:40pm UTC](https://racket.discourse.group/t/pyffi-use-python-from-racket/1362/29 "2022-11-18T14:40:48Z")
@samth The latest commit of `pyffi` uses recorded results from `examples.log` to avoid invoking `pyffi` in the `examples` form. That part works. But ... since I need to document the forms in `pyffi` my Scribble document `manual-pyffi.scbrl` has an for-label dependency on `pyffi`. And that of provokes an error, since `libpython` is not present. At this point I am beginning to think, that the path of least resistance is to ship `pyffi` with a minimal python installation (maybe just the shared library), so the build server doesn't complain. The documentation for the package server suggests delaying the use a the native libary to runtime. So I went looking for examples on the package server without much luck. Is there a nice example of this somewhere? ![image](https://global.discourse-cdn.com/free1/uploads/racket/original/1X/b6f5d1e2700ec0df6ce62bec8f445ecc90972df1.png) ---
**Author:** ![wluker](https://avatars.discourse-cdn.com/v4/letter/w/0ea827/32.png) [@wluker](https://racket.discourse.group/u/wluker)\ **Post date:** [November 18, 2022, 3:01pm UTC](https://racket.discourse.group/t/pyffi-use-python-from-racket/1362/30 "2022-11-18T15:01:45Z")
I think the trick is to install from the `pyffi/pyffi` folder not the top level `pyffi` folder. At least that was the case for me. You'll have to remove the existing install first `raco pkg remove pyffi` and then cd to `pyffi\pyffi` and run `raco pkg install` ---
**Author:** ![soegaard](https://yyz2.discourse-cdn.com/free1/user_avatar/racket.discourse.group/soegaard/32/19_2.png) [@soegaard](https://racket.discourse.group/u/soegaard)\ **Post date:** [November 18, 2022, 3:23pm UTC](https://racket.discourse.group/t/pyffi-use-python-from-racket/1362/31 "2022-11-18T15:23:12Z")
@wluker You are/were right when installing from the Github repo. Yesterday I put `pyffi` on the package server, so (crossed fingers) now you can install pyffi with: ```scheme raco pkg install --no-docs pyffi ``` After configuring `pyffi` with ```scheme raco pyffi configure ``` it is possible to build the documentation with: ```scheme raco setup pyffi ``` A confirmation that the above steps work on macOS and Linux would be nice. I expect the bindings doesn't work on Windows. ---
**Author:** ![wluker](https://avatars.discourse-cdn.com/v4/letter/w/0ea827/32.png) [@wluker](https://racket.discourse.group/u/wluker)\ **Post date:** [November 18, 2022, 5:06pm UTC](https://racket.discourse.group/t/pyffi-use-python-from-racket/1362/32 "2022-11-18T17:06:01Z")
@soegaard I can confirm it installs on Linux with your command sequence given above. `raco setup pyffi` is triggering something, but the documentation is not showing up under `pyffi` with `raco docs`. I noticed it is also not showing up at [https://docs.racket-lang.org/](https://docs.racket-lang.org/) Neat package! ---
**Author:** ![saludes](https://yyz2.discourse-cdn.com/free1/user_avatar/racket.discourse.group/saludes/32/831_2.png) [@saludes](https://racket.discourse.group/u/saludes)\ **Post date:** [November 18, 2022, 5:09pm UTC](https://racket.discourse.group/t/pyffi-use-python-from-racket/1362/33 "2022-11-18T17:09:59Z")
Yes! Now it works for me on Mac OSX 13.0.1 with Python 3.10.6 ---
**Author:** ![samth](https://yyz2.discourse-cdn.com/free1/user_avatar/racket.discourse.group/samth/32/3_2.png) [@samth](https://racket.discourse.group/u/samth)\ **Post date:** [November 18, 2022, 5:26pm UTC](https://racket.discourse.group/t/pyffi-use-python-from-racket/1362/34 "2022-11-18T17:26:54Z")
I think you want to use some combination of the `#:fail` argument to `ffi-lib` and `make-not-available` with `define-ffi-definer` to make the relevant functions error when called rather than when the modules are required. ---
**Author:** ![soegaard](https://yyz2.discourse-cdn.com/free1/user_avatar/racket.discourse.group/soegaard/32/19_2.png) [@soegaard](https://racket.discourse.group/u/soegaard)\ **Post date:** [November 18, 2022, 6:09pm UTC](https://racket.discourse.group/t/pyffi-use-python-from-racket/1362/35 "2022-11-18T18:09:26Z")
@samth > I think you want to use some combination of the `#:fail` argument to `ffi-lib` and `make-not-available` with `define-ffi-definer` to make the relevant functions error when called rather than when the modules are required. I did try that line of attack. I can get `ffi-lib` to return a value that indicates, that the library is not loaded. However `define-ffi-definer` signals an error, when it is passed a non-lib. The `make-not-available` option is for the individual functions. It's possible to cheat - i.e. pass a different library to `define-ffi-definer` but that's at best a hack. Also, in regular use, I'd expect an error when the library is not present. Since `pyffi` is require `for-label` the loading happens before the code in the Scribble file runs - so I don't see a way for the documentation to set a flag suppressing the error. ---
**Author:** ![saludes](https://yyz2.discourse-cdn.com/free1/user_avatar/racket.discourse.group/saludes/32/831_2.png) [@saludes](https://racket.discourse.group/u/saludes)\ **Post date:** [November 19, 2022, 8:40am UTC](https://racket.discourse.group/t/pyffi-use-python-from-racket/1362/36 "2022-11-19T08:40:52Z")
And i can import `sympy`. Thanks! ```scheme #lang racket (require pyffi) (initialize) (post-initialize) (import sympy) (define x (sympy.Symbol "x" #:real #t)) (define pe sympy.parse_expr) (for ([e (list "sin(x)" "cos(x)" "exp(x)" "x**3")]) (let ([e~ (pe e)]) (displayln (cons e~ (sympy.diff e~))))) ``` [Previous page](https://racket.discourse.group/t/pyffi-use-python-from-racket/1362.md?page=1)