# Formatter callback in QT QUI Label widget

**URL:** <https://www.ruby-forum.com/t/formatter-callback-in-qt-qui-label-widget/234520>\
**Category:** GNU Radio\
**Created:** [March 11, 2015, 1:28am UTC](https://www.ruby-forum.com/t/formatter-callback-in-qt-qui-label-widget/234520 "2015-03-11T01:28:12Z")\
**Posts on this page:** 3\
**Page:** 1

<div class="post-metadata">

**Author:** ![addis\_a](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/c4cdca/32.png) [@addis\_a](https://www.ruby-forum.com/u/addis_a)\
**Post date:** [March 11, 2015, 1:28am UTC](https://www.ruby-forum.com/t/formatter-callback-in-qt-qui-label-widget/234520/1 "2015-03-11T01:28:12Z")

</div>

Does the formatter callback work? I can’t get it to do anything useful,  
using a lambda expression stuffed into a variable. How does the widget  
calll the desired function?

---

<div class="post-metadata">

**Author:** ![Marcus\_DSLeech](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/74df32/32.png) [@Marcus\_DSLeech](https://www.ruby-forum.com/u/Marcus_DSLeech)\
**Post date:** [March 11, 2015, 4:18pm UTC](https://www.ruby-forum.com/t/formatter-callback-in-qt-qui-label-widget/234520/2 "2015-03-11T16:18:53Z")

</div>

On Tue, Mar 10, 2015 at 8:26 PM, Marcus D. Leech [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid)  
wrote:

> Does the formatter callback work? I can’t get it to do anything useful,  
> using a lambda expression stuffed into a variable. How does the widget  
> calll the desired function?

Hmm, just tried this and it worked:

lambda x: “Value = {0} (put units here)”.format(perform\_function\_on(x))

So the expression returns a string.

Tom

---

<div class="post-metadata">

**Author:** ![Marcus\_DSLeech](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/74df32/32.png) [@Marcus\_DSLeech](https://www.ruby-forum.com/u/Marcus_DSLeech)\
**Post date:** [March 11, 2015, 4:29pm UTC](https://www.ruby-forum.com/t/formatter-callback-in-qt-qui-label-widget/234520/3 "2015-03-11T16:29:50Z")

</div>

On 03/11/2015 11:16 AM, Tom R. wrote:

> lambda x: “Value = {0} (put units here)”.format(perform\_function\_on(x))
> 
> So the expression returns a string.
> 
> Tom

I actually took a different approach last night that works.

I set the type of the label to string, and have an external variable  
that does the formatting I need, returning a string, and it is that  
string that is used in the Qt label. No formatter callback required.