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Make a python class constructor

Source: R/py-classes.R
grapes-py_class-grapes.Rd

Make a python class constructor

Usage

spec %py_class% body

Arguments

spec

a bare symbol MyClassName, or a call MyClassName(SuperClass)

body

an expression that can be evaluated to construct the class methods.

Value

The python class constructor, invisibly. Note, the same constructor is also assigned in the parent frame.

See also

%<-active%()

Examples

if (FALSE) {
MyClass %py_class% {
  initialize <- function(x) {
    print("Hi from MyClass$initialize()!")
    self$x <- x
  }
  my_method <- function() {
    self$x
  }
}

my_class_instance <- MyClass(42)
my_class_instance$my_method()

MyClass2(MyClass) %py_class% {
  "This will be a __doc__ string for MyClass2"

  initialize <- function(...) {
    "This will be the __doc__ string for the MyClass2.__init__() method"
    print("Hi from MyClass2$initialize()!")
    super$initialize(...)
  }
}

my_class_instance2 <- MyClass2(42)
my_class_instance2$my_method()

reticulate::py_help(MyClass2) # see the __doc__ strings and more!

# In addition to `self`, there is also `private` available.
# This is an R environment unique to each class instance, where you can
# store objects that you don't want converted to Python, but still want
# available from methods. You can also assign methods to private, and
# `self` and `private` will be available in private methods.

MyClass %py_class% {

  initialize <- function(x) {
    print("Hi from MyClass$initialize()!")
    private$y <- paste("A Private field:", x)
  }

  get_private_field <- function() {
    private$y
  }

  private$a_private_method <- function() {
    cat("a_private_method() was called.\n")
    cat("private$y is ", sQuote(private$y), "\n")
  }

  call_private_method <- function()
    private$a_private_method()

  # equivalent of @property decorator in python
  an_active_property %<-active% function(x = NULL) {
    if(!is.null(x)) {
      cat("`an_active_property` was assigned", x, "\n")
      return(x)
    } else {
      cat("`an_active_property` was accessed\n")
      return(42)
    }
  }
}

inst1 <- MyClass(1)
inst2 <- MyClass(2)
inst1$get_private_field()
inst2$get_private_field()
inst1$call_private_method()
inst2$call_private_method()
inst1$an_active_property
inst1$an_active_property <- 11
}