Points-to-lines-script_QGIS3

from qgis.PyQt.QtCore import QVariant

# variables
layer_name = "My_layer_name"
line_field_name = "Line"
m_threshold = 0.5
new_name = "new_lines"
order_variable="Fiducial"

# find point vector layer
vl = QgsProject.instance().mapLayersByName(layer_name)[0]

# create a new line layer
crs = vl.crs().authid()
vline = QgsVectorLayer("multilinestring?crs=" + crs, new_name , "memory")
pr = vline.dataProvider()
pr.addAttributes([QgsField(line_field_name, QVariant.String)])
vline.updateFields()

new_geometry = QgsGeometry()

idx = vl.fields().indexOf(line_field_name)
line_values = vl.uniqueValues(idx)

for line in line_values:
    # init for
    expr = QgsExpression('"' + line_field_name + '"= \'' + line + '\'')
    request = QgsFeatureRequest(expr)
    request.addOrderBy(order_variable)
    wkt = "MultiLineString (("
    previous_linename = None
    previous_geometry = None

    for feat in vl.getFeatures(request):

        if previous_linename is not None:
            segment = feat.geometry().shortestLine(previous_geometry)

            if segment.length() > m_threshold:
                # delete last comma and begin next part
                wkt = wkt[:-1] + "),("

            pt = feat.geometry().asPoint()
            wkt += str(pt.x()) + " " + str(pt.y()) + ","

        previous_linename = line
        previous_geometry = feat.geometry()
        pt = feat.geometry().asPoint()
        wkt += str(pt.x()) + " " + str(pt.y()) + ","


    # delete last comma and close wkt
    wkt = wkt[:-1] + "))"
    new_feat = QgsFeature()
    new_feat.setGeometry(QgsGeometry.fromWkt(wkt))
    new_feat.setAttributes([previous_linename])
    pr.addFeature(new_feat)

# update extent for the new line layer
vline.updateExtents()
# load new line layer to canvas
QgsProject.instance().addMapLayer(vline)