Python 代码块生成的图片不支持 caption? 自然也不支持图片的引用

在 knitr::opts_chunk 中设置 python.reticulate = TRUE 意味着所有的 Python 代码块共享一个 Python Session（好特性），而 python.reticulate = FALSE 意味着使用 knitr 提供的 Python 引擎，所有的 Python 代码块独立运行。

下面提供一个可复现问题的例子

---
title: "Untitled"
output: html_document
---

```{r setup, include=FALSE}
knitr::opts_chunk$set(
  echo = TRUE,
  python.reticulate = TRUE
)
```

## R Markdown

```{python math}
import numpy as np
import matplotlib.pyplot as plt
plt.switch_backend('agg')
```

matplotlib 绘图

```{python math-demo,eval=FALSE}
t = np.arange(0.0, 2.0, 0.01)
s = np.sin(2*np.pi*t)

plt.plot(t,s)
plt.title(r'$\alpha_i > \beta_i$', fontsize=20)
plt.text(1, -0.6, r'$\sum_{i=0}^\infty x_i$', fontsize=20)
plt.text(0.6, 0.6, r'$\mathcal{A}\mathrm{sin}(2 \omega t)$',
         fontsize=20)
plt.xlabel('time (s)')
plt.ylabel('volts (mV)')
plt.show()
```


```{python demo-matplotlib, ref.label = 'math-demo', fig.cap = "数学公式", eval = TRUE, echo = FALSE}
```

环境信息

xfun::session_info(c('rmarkdown','reticulate'))

R version 3.6.0 (2019-04-26)
Platform: x86_64-w64-mingw32/x64 (64-bit)
Running under: Windows 8.1 x64 (build 9600)

Locale:
  LC_COLLATE=Chinese (Simplified)_China.936 
  LC_CTYPE=Chinese (Simplified)_China.936   
  LC_MONETARY=Chinese (Simplified)_China.936
  LC_NUMERIC=C                              
  LC_TIME=Chinese (Simplified)_China.936    

Package version:
  base64enc_0.1.3 digest_0.6.18   evaluate_0.13   glue_1.3.1     
  graphics_3.6.0  grDevices_3.6.0 grid_3.6.0      highr_0.8      
  htmltools_0.3.6 jsonlite_1.6    knitr_1.22      lattice_0.20.38
  magrittr_1.5    markdown_0.9    Matrix_1.2.17   methods_3.6.0  
  mime_0.6        Rcpp_1.0.1      reticulate_1.12 rmarkdown_1.12 
  stats_3.6.0     stringi_1.4.3   stringr_1.4.0   tinytex_0.13   
  tools_3.6.0     utils_3.6.0     xfun_0.7        yaml_2.2.0     

Pandoc version: 2.7.2

我感觉这个问题应该和环境信息关系不大，也和 Python 环境信息无关

xfun::session_info(c('knitr','rmarkdown','reticulate'))

R Under development (unstable) (2019-05-10 r76484)
Platform: x86_64-pc-linux-gnu (64-bit)
Running under: Fedora 30 (Thirty), RStudio 99.9.9

Locale:
  LC_CTYPE=zh_CN.UTF-8       LC_NUMERIC=C               LC_TIME=zh_CN.UTF-8        LC_COLLATE=zh_CN.UTF-8    
  LC_MONETARY=zh_CN.UTF-8    LC_MESSAGES=zh_CN.UTF-8    LC_PAPER=zh_CN.UTF-8       LC_NAME=C                 
  LC_ADDRESS=C               LC_TELEPHONE=C             LC_MEASUREMENT=zh_CN.UTF-8 LC_IDENTIFICATION=C       

Package version:
  base64enc_0.1.3        digest_0.6.18          evaluate_0.13          glue_1.3.1            
  graphics_3.7.0         grDevices_3.7.0        grid_3.7.0             highr_0.8             
  htmltools_0.3.6        jsonlite_1.6           knitr_1.22.15          lattice_0.20.38       
  magrittr_1.5           markdown_0.9           Matrix_1.2.17          methods_3.7.0         
  mime_0.6               Rcpp_1.0.1             reticulate_1.12.0.9000 rmarkdown_1.12        
  stats_3.7.0            stringi_1.4.3          stringr_1.4.0          tinytex_0.13          
  tools_3.7.0            utils_3.7.0            xfun_0.7               yaml_2.2.0            

Pandoc version: 2.3.1

参考 https://github.com/yihui/knitr/blob/332e28c647d85ae3937b1bcd7ac61c0aea54d897/NEWS.md#major-changes-4