Hi,t-set can be used to define a new variable and set its value:

Syntax is,

<t t-set=”variable_name” t-value=”value of the variable” />

Example: 

<t t-set=”count” t-value=”0” />  

This will create a new variable ‘count’ and set its value as zero. We can set the value of this variable using a function.

<t t-set=”count” t-value=”my_function()” />

Here, the value of ‘count’ will be the value returned from the function ‘my_function’. When we define a variable, we don’t need to specify a specific type of this variable. We can have several types of values such as numbers, strings, arrays (lists) and dictionaries, etc. If we need to define a dictionary, we can do it like this,

<t t-set=”my_dict” t-value=”{'my': 'first', 'my2': 'second' }” />

Just like this, we can use lists also. Iterating over the different values of a list or dictionary can be achieved by using a loop.

Hope it helps

Thank you, Savya Sachin!  

When I use expressions like

xpath expr="//label[@for="name"]" position="attributes"

attribute name="string" FIO /attribute

/xpath

(i removed tags)

everything works, but when I insert an expression

xpath expr="//field[@name="name"]" position="after"

t t-set="my_label" Leads /t

/xpath

an error occurs

The forbidden owl directive used in arch (t-set).

Hi,

t-set: This attribute signifies that you're using a QWeb directive for setting a variable

t-value: This attribute is used to define the value you want to assign to the variable

You can find many examples of t-set in the default odoo addons code, find an example below for your reference

Thanks