A script to make fields with year, day of year and decimal hour from a epoch field in QGIS

qgistimefields.py

# From a layer with a timestamp as an epoch number,
# adds in fields for year, day of year and decimal hour if they do not exist yet
# goes through the dataset, calculate the year, doy and hour and populates the fields
import datetime
epochfield = 'acqtime'
layer = qgis.utils.iface.activeLayer()
if layer.dataProvider().fieldNameIndex(epochfield) == -1:
    # Do not want to do anything on a layer without an epoch field
    print(f'Data layer does not have an "{epochfield}" field')
else:
    stopEditing = False
    if not layer.isEditable():
        stopEditing = True
        layer.startEditing()
    if layer.dataProvider().fieldNameIndex("year") == -1:
        layer.dataProvider().addAttributes([QgsField("year", QVariant.Int)])
    if layer.dataProvider().fieldNameIndex("doy") == -1:
        layer.dataProvider().addAttributes([QgsField("doy", QVariant.Int)])
    if layer.dataProvider().fieldNameIndex("hour") == -1:
        layer.dataProvider().addAttributes([QgsField("hour", QVariant.Double)])
    layer.updateFields()
    for feature in layer.getFeatures():
        epoch = feature[epochfield]
        epoch = int(epoch)
        rectime = datetime.datetime.fromtimestamp(epoch)
        year = rectime.strftime('%Y')
        feature['year'] = int(year)
        doy = rectime.strftime('%j')
        feature['doy'] = int(doy)
        hour = rectime.strftime('%H')
        minute = rectime.strftime('%M')
        second = rectime.strftime('%S')
        dechour = int(hour)+int(minute)/60 + float(second)/3600
        feature['hour'] = dechour 
        layer.updateFeature(feature)
    layer.commitChanges(stopEditing)
    # stopEditing signals if the editing should or should not be active
    # after the commit