Update python format option (#3452)

close #3429

autoload/SpaceVim/layers/lang/python.vim

@@ -140,7 +140,7 @@ function! s:language_specified_mappings() abort
   if s:format_on_save
     augroup SpaceVim_layer_lang_python
       autocmd!
-      autocmd BufWritePost *.py Neoformat yapf
+      autocmd BufWritePre *.py undojoin | Neoformat
     augroup end
   endif
 

docs/cn/layers/lang/python.md

@@ -73,6 +73,17 @@ pip install --user flake8
 pip install --user yapf
 ```
 
+如果需要使用其他命令作为格式化工具，比如`black`命令，可以在启动函数中进行配置：
+
+```viml
+let g:neoformat_python_black = {
+    \ 'exe': 'black',
+    \ 'stdin': 1,
+    \ 'args': ['-q', '-'],
+    \ }
+let g:neoformat_enabled_python = ['black']
+```
+
 **格式化导包：**
 
 若需要更便捷地删除未使用的 imports，需要安装 [autoflake](https://github.com/myint/autoflake)：

docs/layers/lang/python.md

@@ -72,6 +72,18 @@ load this layer with setting `format_on_save` to `1`.
 pip install --user yapf
 ```
 
+To use other tool as the format command, for example `black`, change the neoformat option in bootstrap
+function.
+
+```viml
+let g:neoformat_python_black = {
+    \ 'exe': 'black',
+    \ 'stdin': 1,
+    \ 'args': ['-q', '-'],
+    \ }
+let g:neoformat_enabled_python = ['black']
+```
+
 **format imports:**
 
 To be able to suppress unused imports easily, install [autoflake](https://github.com/myint/autoflake):