Learn Vim at your own pace with my self-study Core Vim Course.

Learn more

Learn Vim at your own pace with my self-study Core Vim Course.

Using Python interpolation in UltiSnips snippets


Run time:

UltiSnips can execute Python code and interpolate the result into a snippet. This makes it possible to create snippets that react to the text entered in each field. We’ll look at an example that performs a simple calculation and inserts the result into our document.


The basics of Python interpolation in UltiSnips

Python scripts can be embedded inside UltiSnips snippets using `!p`. In this context, UltiSnips predefines a few Python objects and variables for us. For example, the snip.rv variable stands for return value. It represents the text that will be interpolated into the document when our snippet is expanded. The t variable is a list representing the values of tabstops numbered one, two, three, and so on. For more details, look up :help UltiSnips-python.

A snippet to calculate average typing speed

The snippet that I demonstrated in the video appeared in text.snippets like this:

global !p
def fraction(a, b):
        return "%.1f" % (float(a)/float(b))
    except (ValueError, ZeroDivisionError):
        return "ERR"

snippet 75wrds "Log a 750words.com session" b
750words.com: ${1:750} words in ${2:20} minutes - `!p
snip.rv = fraction(t[1], t[2])
` wpm.

The global block allows us to create Python functions, which we can then call from any snippet in the same snippet file. This fraction() function attempts to cast two arguments to floats and divide one by the other, rounding the result to a single decimal place. If it encounters an exception, it returns the string “ERR”.

When using this snippet, the words-per-minute calculation is updated in real-time as the values for tabstops one and two are changed. It’s almost like working with a spreadsheet!

Sharing helper functions between snippet files

The fraction() function defined above would be available only to snippets defined in the text.snippets file. We could make that function available to other snippet files by moving it into a ~/.vim/pythonx/snippet_helpers.py file:

def fraction(a, b):
        return "%.1f" % (float(a)/float(b))
    except (ValueError, ZeroDivisionError):
        return "ERR"

We could then import this into a snippet file by including this:

global p!
from snippet_helpers.py import *

One potential gotcha to watch out for here is that Vim will load the snippet_helpers.py one time only. That means that any changes you make to the helper functions in snippet_helpers.py won’t be seen by your snippet files until you reboot Vim. Despite that limitation, this mechanism is still useful for sharing helper functions between your snippet files.

Further reading

  • UltiSnips
  • :h UltiSnips-interpolation
  • :h UltiSnips-python
  • :h UltiSnips-globals

I’d like to thank Holger Rapp for his great feedback on early drafts of this screencast.


Level-up your Vim


Boost your productivity with a Vim training class. Join a public class, or book a private session for your team.

Drew hosted a private Vim session for the shopify team that was one of the best workshops I have ever attended.

John Duff, Director of Engineering at Shopify


Make yourself a faster and more efficient developer with the help of these publications, including Practical Vim (Pragmatic Bookshelf 2012), which has over 50 five-star reviews on Amazon.

After reading it, I've switched to vim as my default editor on a daily basis with no regrets. ★★★★★

Javier Collado

Learn to use Vim efficiently in your Ruby projects

In association with thoughtbot, one of the most well respected Rails consultancies in the world, I've produced a series of screencasts on how to make navigating your Ruby projects with Vim ultra-efficient. Along the way, you’ll also learn how to make Ruby blocks a first-class text object in Vim. This lets you edit Ruby code at a higher level of abstraction. Available to buy from thoughtbot..