tests/testthat/test-python-iterators.R

In reticulate: Interface to 'Python'

context("iterators")

test_that("Iterators reflect values back", {
  skip_if_no_python()
  rlist <- list("foo", "bar", 42L)
  expect_equal(iterate(test$makeIterator(rlist)), rlist)
})


test_that("Generators reflect values back", {
  skip_if_no_python()
  expect_equal(as.integer(iterate(test$makeGenerator(5))) + 1L, seq(5))
})


test_that("Iterators are drained of their values by iteration", {
  skip_if_no_python()
  iter <- test$makeIterator(c(1:5))
  a <- iterate(iter)
  b <- iterate(iter)
  expect_length(b, 0)
})


test_that("infinite iterators can be accessed with iter_next", {
  skip_if_no_python()

  # create an infinite generator
  main <- py_run_string("
def infinite_generator():
  n = 0
  while True:
    yield n
    n += 1
")
  it <- main$infinite_generator()

  # iterate and stop when i is 10
  while(TRUE) {
    i <- iter_next(it)
    if (i == 10) break
  }
  expect_equal(i, 10)
})

test_that("iter_next returns sentinel value when it completes", {
  skip_if_no_python()
  iter <- test$makeIterator(c(1:5))
  while (TRUE) {
    item <- iter_next(iter, NA)
    if (is.na(item))
      break
  }
  expect_equal(item, NA)
})

test_that("python iterables can be iterated", {
  skip_if_no_python()
  builtins <- import_builtins(convert = FALSE)
  range <- builtins$range(1L, 10L)
  result <- iterate(range)
  expect_length(result, 9)
})

sequence_generator <-function(start, completed = NULL) {
  value <- start
  function() {
    value <<- value + 1L
    gc()
    if (value < 20L)
      value
    else
      completed
  }
}

test_that("generator functions iterate as expected", {
  skip_if_no_python()
  gen <- py_iterator(sequence_generator(10L))
  expect_equal(iterate(gen), 11L:19L)
})


test_that("generator functions support a custom completed value", {
  skip_if_no_python()
  gen <- py_iterator(sequence_generator(10L, completed = NA), completed = NA)
  expect_equal(iterate(gen), 11L:19L)
})

test_that("generator functions are always called on the main thread", {
  skip_if_no_python()
  gen <- py_iterator(sequence_generator(10L))
  expect_equal(test$iterateOnThread(gen), 11L:19L)
})

test_that("can't supply a function with arguments", {
  expect_error(
    py_iterator(function(x) x),
    "no arguments"
  )
})