rxp_py: Create a Nix Expression Running a Python Function

In rixpress: Build Reproducible Analytical Pipelines with 'Nix'

Create a Nix Expression Running a Python Function

Description

Create a Nix Expression Running a Python Function

Usage

rxp_py(
  name,
  expr,
  additional_files = "",
  user_functions = "",
  nix_env = "default.nix",
  encoder = NULL,
  decoder = NULL,
  env_var = NULL,
  noop_build = FALSE
)

Arguments

name	Symbol, name of the derivation.
expr	Character, Python code to generate the expression. Ideally it should be a call to a pure function. Multi-line expressions are not supported.
additional_files	Character vector, additional files to include during the build process. For example, if a function expects a certain file to be available, this is where you should include it.
user_functions	Character vector, user-defined functions to include. This should be a script (or scripts) containing user-defined functions to include during the build process for this derivation. It is recommended to use one script per function, and only include the required script(s) in the derivation.
nix_env	Character, path to the Nix environment file, default is "default.nix".
encoder	Character, defaults to NULL. The name of the Python function used to serialize the object. It must accept two arguments: the object to serialize (first), and the target file path (second). If NULL, the default behaviour uses pickle.dump. Define this function in functions.py. See vignette("encoding-decoding") for more details.
decoder	Character or named vector/list, defaults to NULL. Can be: A single string for the Python function to unserialize all upstream objects A named vector/list where names are upstream dependency names and values are their specific unserialize functions If NULL, the default uses pickle.load. See vignette("encoding-decoding") for more details.
env_var	Character vector, defaults to NULL. A named vector of environment variables before running the Python script, e.g., c(PYTHONPATH = "/path/to/modules"). Each entry will be added as an export statement in the build phase.
noop_build	Logical, defaults to FALSE. If TRUE, the derivation produces a no-op build (a stub output with no actual build steps). Any downstream derivations depending on a no-op build will themselves also become no-op builds.

Details

At a basic level, rxp_py(mtcars_am, "mtcars.filter(polars.col('am') == 1).to_pandas()") is equivalent to ⁠mtcars_am = mtcars.filter(polars.col('am') == 1).to_pandas()⁠. rxp_py() generates the required Nix boilerplate to output a so-called "derivation" in Nix jargon. A Nix derivation is a recipe that defines how to create an output (in this case mtcars_am) including its dependencies, build steps, and output paths.

Value

An object of class derivation which inherits from lists.

See Also

Other derivations: rxp_jl(), rxp_jl_file(), rxp_py_file(), rxp_qmd(), rxp_r(), rxp_r_file(), rxp_rmd()

Examples

## Not run: 
  rxp_py(
    mtcars_pl_am,
    expr = "mtcars_pl.filter(polars.col('am') == 1).to_pandas()"
  )

  # Skip building this derivation
  rxp_py(
    data_prep,
    expr = "preprocess_data(raw_data)",
    noop_build = TRUE
  )

  # Custom serialization
  rxp_py(
    mtcars_pl_am,
    expr = "mtcars_pl.filter(polars.col('am') == 1).to_pandas()",
    user_functions = "functions.py",
    encoder = "serialize_model",
    additional_files = "some_required_file.bin")

## End(Not run)

rixpress documentation built on Feb. 19, 2026, 9:06 a.m.