Vim Setup for Python

I have used a number of modern IDEs for software development.  For example, I think it is neat how one can draw up UML diagrams and generate code from them (or vice versa).  Integration with the-more-complex revision control systems is also nice.  What I dislike is vendor lock in loss of control of the development flow.  I could speak more about this, but it is a different topic than what I'd like to cover today.

I like the Vim editor because of it's point tool nature.  It does it's job and it does it well.  It is well supported by the community, it is available on virtually every Linux installation (and Windows), and it is extremely customization.

A number of blog posts have been written that describe their settings for configuring Vim to edit Python files. This will be yet another.  The default configuration for Python in Vim leaves to be desired.  Fortunately, there are a few easy steps one can take to enable a streamlined experience.

The first step is to make sure to enable the Vim filetype plugin using command filetype plugin indent on in your $HOME/.vimrc.  The following site has more information about why to use this plugin.  To summarize, it allows the user to move filetype-specific commands outside of their main configuration file, reducing clutter in the file.

http://vim.wikia.com/wiki/Keep_your_vimrc_file_clean

For indentation, first create a Python-specific configuration file $HOME/.vim/ftplugin/python.vim containing the following lines:

setlocal tabstop=4

setlocal softtabstop=4

setlocal shiftwidth=4

setlocal textwidth=79 " to comply with PEP-8 style guide

setlocal smarttab

setlocal expandtab

Eric McSween developed a Vim plugin for smart indentation of  Python code.  The utility is available here: http://www.vim.org/scripts/script.php?script_id=974.  Installation is straightforward, simply download the latest version of the script and copy the file to $HOME/.vim/indent/python.vim.  Use of the filetype plugin, as described above, will automatically enable the utility.

Last, Dmitry Vasiliev developed a Vim plugin for Python syntax highlighting.  The utility is available here: http://www.vim.org/scripts/script.php?script_id=790.  To install the plugin, download the latest version of the script and copy the file to $HOME/.vim/syntax/python.vim.  Enable the plugin by adding command syntax on to your $HOME/vim.rc file.

I recommend the use of a static code analyzer for anyone developing new code.  Pylint is my analysis tool of choice.  It is typically available as a binary package in most Linux distros - i.e. may need to talk to your sys admin.  There is some overhead of using code analysis in the short term, but long term, you will benefit from a code base with that looks pretty and smells less.

For integration with my editor, I use the following plugin: http://www.vim.org/scripts/script.php?script_id=891.  Installation of the plugin and requires the user to copy the downloaded script to directory $HOME/.vim/compiler. 

Vim Setup for SystemVerilog

It took some time and effort on my part to really become comfortable with using Vim.  Eventually, I became so productive with using the text editor that it became unnecessary to use anything besides it.

The two features that got me hooked to the text editor are the ability the select and manipulate columns in visual block mode and the large number of third-party plugins available.  My primary use for Vim is for programming in SystemVerilog.  I have found that the following plugins are extremely useful:

• matchit.vim (http://www.vim.org/scripts/script.php?script_id=39)
• verilog_systemverilog.vim (http://www.vim.org/scripts/script.php?script_id=1586)
• vcscommand.vim (http://www.vim.org/scripts/script.php?script_id=90)

The typical use of the % key in Vim is to move the cursor between matching curly braces.  I have a seen a number of SystemVerilog users adopt the following convention to make use of the feature.  It is a cumbersome practice that is entirely avoidable.

if (condition) begin // {
end // }

When configured correctly, match_it.vim allows the % key to be configured to match more than just single characters.  In the context of SystemVerilog, we can enable the user to move the cursor between Verilog-style statements that define blocks of code (e.g. begin/end, class/endclass, package/endpackage, etc.)

Configuring the plugin is pretty straightforward.  I started with the configuration posted at http://vblog.learn-asic.com/?p=40 and made some minor tweaks (make sure to use the tick character ', not `, ‘, or ’ when defining b:match_words).

filetype plugin on

source ~/.vim/plugin/matchit.vim
if exists('loaded_matchit')
let b:match_ignorecase=0
let b:match_words=
  \ '\<begin\>:\<end\>,' .
  \ '\<if\>:\<else\>,' .
  \ '\<module\>:\<endmodule\>,' .
  \ '\<class\>:\<endclass\>,' .
  \ '\<program\>:\<endprogram\>,' .
  \ '\<clocking\>:\<endclocking\>,' .
  \ '\<property\>:\<endproperty\>,' .
  \ '\<sequence\>:\<endsequence\>,' .
  \ '\<package\>:\<endpackage\>,' .
  \ '\<covergroup\>:\<endgroup\>,' .
  \ '\<primitive\>:\<endprimitive\>,' .
  \ '\<specify\>:\<endspecify\>,' .
  \ '\<generate\>:\<endgenerate\>,' .
  \ '\<interface\>:\<endinterface\>,' .
  \ '\<function\>:\<endfunction\>,' .
  \ '\<task\>:\<endtask\>,' .
  \ '\<case\>\|\<casex\>\|\<casez\>:\<endcase\>,' .
  \ '\<fork\>:\<join\>\|\<join_any\>\|\<join_none\>,' .
  \ '`ifdef\>:`else\>:`endif\>,'
endif

I only use the syntax plugin included in the verilog_systemverilog.vim package because I am disciplined enough to do a better job than the tool can.  The automation identation functionality gets in the way for me.  My filetype configuration for SystemVerilog files is as follows:

syntax on


autocmd BufRead,BufNewFile *.v,*.vh setfiletype verilog
autocmd BufRead,BufNewFile *.v,*.vh set expandtab tabstop=4 softtabstop=2 shiftwidth=2
autocmd BufRead,BufNewFile *.sv,*.svi set filetype=verilog_systemverilog
autocmd BufRead,BufNewFile *.sv,*.svi set expandtab tabstop=4 softtabstop=2 shiftwidth=2

I prefer spaces to tabs for the simple reason that the only way to align a a block of code idented with tabs is to use spaces, so why use tabs to begin with?  The only exception that I have found to the rule is for assembly languages and makefiles (because they require the use of the tab character).  Opinions vary widely on the subject, but the most important take away is to be aware of how the original author of the file that you are editing has chosen to ident their code and to not deviate from it.  To view the type of whitespace used for the file being edited, you can set these options in your .vimrc:

set listchars=eol:$,tab:\>\ ,trail:.,extends:>,precedes:<
set list   " to turn on (use :set nolist to turn off)


The last plugin that I have decided to blog about is vcscommand.vim (not to be confused with the simulator from Synopsys).  This plugin script is an excellent front end to CVS, SVN, and other source code control systems.  The feature that I use the most is command :VCSVimDiff to display differences between the most recent version of the file and the checked-in version of the file.  I map this command to key F12.  There are other options for file check in but I'll typically use the command line to do so.

map <F12> :VCSVimDiff<CR> " map F12