pyRevit Snippet: Validate a Parameter Exists Before Writing to It

Batch parameter writes fail for one boring reason: a handful of elements don’t carry the parameter. The script crashes at element 847 of 2,000, and now your model is half-updated inside an open transaction.

The Guard Clause

def set_param_safe(element, param_name, value):
    param = element.LookupParameter(param_name)
    if param is None or param.IsReadOnly:
        return False
    param.Set(value)
    return True

Using It in a Batch Run

from pyrevit import revit, DB

elements = DB.FilteredElementCollector(revit.doc)\
    .OfCategory(DB.BuiltInCategory.OST_DuctTerminal)\
    .WhereElementIsNotElementType()\
    .ToElements()

skipped = []
with revit.Transaction('Update AHU zone tags'):
    for el in elements:
        if not set_param_safe(el, 'TBT_Zone', 'AHU-01'):
            skipped.append(el.Id.IntegerValue)

if skipped:
    print('Skipped {} elements: {}'.format(len(skipped), skipped[:20]))

Why Not try/except?

A bare try/except hides why the write failed — read-only parameter, missing parameter, or wrong storage type all look identical. The explicit check costs one line and gives you a skip list you can hand to the modeler responsible.

One More Trap

LookupParameter returns the first parameter with that name. If a family has both an instance and a type parameter named TBT_Zone, you may write to the wrong one. Prefix shared parameter names by discipline (TBT_) and never duplicate names between instance and type.