BathAfrica: Add rewritten practical lesson with steps, code and expected results

2026-10-29T21:00:54Z

Add rewritten practical lesson with steps, code and expected results

New page

__NOTOC__
{{OpenSite scope}}
{{OpenSite lesson
|id=opensite.help.quantities-and-profiles
|summary=Add quantities written in different units and change their display profile without changing their physical values.
|prerequisites=Embedded OpenSite Python. This lesson does not require a document or a development authorization policy.
|steps==== Enter units explicitly ===
Use <code>parse_quantity</code> or <code>Q</code> rather than assuming that 450 means millimetres. The example combines 3.2 m with 450 mm.

=== Add compatible quantities ===
The units engine converts compatible lengths to canonical SI before adding them. Expected total: 3.65 m, or 3650 mm.

=== Change presentation ===
Switch to <code>engineering_metric</code> and format the same quantity. Store and compare its SI value before and after. Displaying millimetres must not scale the model.

=== Handle a rejected unit ===
Check the unit spelling, physical dimension and quantity kind. Pressure is not a length; absolute temperature differs from a temperature difference.

|result=The script prints 3650 mm. Its assertions confirm an SI total of 3.65 m and unchanged SI after selecting the display profile.
|limitations=Profiles affect presentation. They do not choose a national design standard. The script changes the current profile for this session; return to your preferred profile afterwards.
}}

== Complete example ==
{{Code|lang=python|code=<nowiki>import opensite

span = opensite.parse_quantity("3.2 m")
extension = opensite.parse_quantity("450 mm")
total = opensite.add(span, extension)
print(f"Total: {total.value_in('mm'):.0f} mm")
assert abs(total.si_value - 3.65) < 1e-12

before = total.si_value
opensite.execute("units.set_profile", {"profile": "engineering_metric"})
print("Display:", opensite.format_quantity(total, "engineering_metric"))
assert total.si_value == before</nowiki>}}

<div class="os-page-nav">{{Docnav|OpenSite/Guides/First document|OpenSite/Guides/Create a material|OpenSite/Guides|All guides}}</div>
[[Category:OpenSite documentation]]

OpenSite/Guides/Quantities and profiles - Revision history

BathAfrica: Add rewritten practical lesson with steps, code and expected results