runr test with persistent python3

persist.rmd

---
title: "runr test"
date: "`r format(Sys.time(), '%H:%M %d %B %Y ')`"
author: Ben Bolker
---

```{r opts,message=FALSE,echo=FALSE,warning=FALSE}
library("knitr")
library("runr")
py <- proc_python()
py$start()
knit_engines$set(python = function(options) {
    knitr:::wrap(py$exec(options$code), options)
})
opts_chunk$set(tidy=FALSE,engine='python',engine.path='python3')

```

```{r chunk1}
a = 1
```

```{r chunk2}
print(a)
```

```{r chunk3,engine="R"}
runif(1)
```