Multi-line labeling of a shapefile layer with pyQGis

Question

I want to label a shp layer on two lines with pyQGis. I managed to do it with only one field, but with two or more fields (using concat) it does not work anymore.

Here is the code I wrote:

def labelLine (lyr, fieldNom1, fieldNom2):
  # This function shows the labels of 2 fields "fieldName1" and "fieldName2" for a Line layer lyr
  label = QgsPalLayerSettings ()
  label.readFromLayer (lyr)
  label.enabled = True
  # we concatenate the two fields
  label.fieldName = "concat ('BASE:', fieldName1, '\\ n', 'L =', fieldName2, 'm')"
  label.placement = QgsPalLayerSettings.Line
  label.bufferDraw = True
  label.bufferSize = 1
  label.setDataDefinedProperty (QgsPalLayerSettings.S ize, True, True, '8', '')
  label.writeToLayer (lyr)

Maybe try replacing \\ n with \n? So label.fieldName = "concat('BASE:', fieldName1, '\n', 'L =', fieldName2, 'm')". — Joseph, Oct 17 '17 at 11:07
What happens when you use it? Is it still on a single line? Is there an error in the expression? Maybe you can post a screenshot of how the label looks? — Joseph, Oct 17 '17 at 13:30
This question is a duplicate of https://gis.stackexchange.com/questions/132905/multiline-field-name-label-referencing — YoLecomte, Oct 17 '17 at 20:53

YoLecomte · Answer 1 · 2017-10-17T20:41:42.187

3

What about using the wrapChar() method of QgsPalLayerSettings (http://qgis.org/api/2.18/classQgsPalLayerSettings.html) You can set a character that is intended to wrap the label string

something like:

label.wrapChar = '*'

and then in your code:

label.fieldName = "concat ('BASE:', fieldName1, '*', 'L =', fieldName2, 'm')"

then run, it may work

edited Oct 17 '17 at 20:41

answered Oct 17 '17 at 19:05

YoLecomte

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Unfortunetly, after the code compilation, I received the following error: – ennine Oct 17 '17 at 19:38
label. WrapChar('*') AttributeError: 'QgsPalLayerSettings' object has no attribute 'WrapChar' – ennine Oct 17 '17 at 19:39
Remove the upper W and replace with lower w – YoLecomte Oct 17 '17 at 19:45
When I replace WrapChar by wrapChar, I receive the following error: label. wrapChar('*') TypeError: 'unicode' object is not callable – ennine Oct 17 '17 at 19:45
if you do a copy/paste of the error, you have a space between the dot and wrapChar... remove it. – YoLecomte Oct 17 '17 at 20:03
Ok, my fault, please see my edited answer and try with it. label.wrapChar = '*' I test it and it work! – YoLecomte Oct 17 '17 at 20:18
Now, I have no error after the code compilation, but still the labels do not appear in QGis. However, when I investigate the property layer/Labelling, I notice that the expression is as follows: concat ('BASE:', fieldName1, '*', 'L =', fieldName2, 'm'). It seems that fieldName1 & fieldName2 are not recognised as fields. – ennine Oct 17 '17 at 20:54
Can you provide the whole code you use? – YoLecomte Oct 17 '17 at 21:01
You kindly find below the written code (comments are written in french): – ennine Oct 17 '17 at 21:06
Sorry, I can not transmit the code because it is too long. – ennine Oct 17 '17 at 21:10
Edit your question With the updated code – YoLecomte Oct 17 '17 at 21:13
I try to attach the code but it seems that I exceeded the size limit of sending – ennine Oct 17 '17 at 21:52
Attach it in the question, not in the comment. How long is it?? – YoLecomte Oct 18 '17 at 05:32

Joseph · Accepted Answer · 2017-10-23T14:37:29.677

3

Perhaps try something like the following expression. We can use the to_string function from the Field Calculator to convert any value from a field to a string (as you can't concatenate strings and values):

'''concat('BASE: ' + to_string("''' + fieldName1 + '''"),'\nL = ' + to_string("''' + fieldName2 + '''") + 'm')'''

So your code could look like:

def labelLine(lyr, fieldName1, fieldName2):
    label = QgsPalLayerSettings()
    label.readFromLayer(lyr)
    label.enabled = True
    label.fieldName = '''concat('BASE: ' + to_string("''' + fieldName1 + '''"),'\nL = ' + to_string("''' + fieldName2 + '''") + 'm')'''
    label.placement = QgsPalLayerSettings.Line
    label.bufferDraw = True
    label.bufferSize = 1
    label.setDataDefinedProperty(QgsPalLayerSettings.Size, True, True, '8', '')
    label.writeToLayer(lyr)
    lyr.setCustomProperty("labeling/drawLabels", True)
    lyr.triggerRepaint()

lyr = iface.activeLayer()
labelLine(lyr, 'fieldName1', 'fieldName2')

Example:

edited Oct 23 '17 at 14:37

answered Oct 19 '17 at 10:09

Joseph

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Many thanks Joseph for your very helpful code. However, the label do not appear automatically in QGis and I have to switch the Layer Properties/Labels, and toggle OK. I try to add the following to confirm the changes but it does not work: layer.triggerRepaint() or layer.commitChanges() layer.updateExtents() Any help would be appreciated. – ennine Oct 23 '17 at 14:08
1

@ennine - Most welcome! Edited the post to include additional lines of code which should hopefully enable and draw the labels :) – Joseph Oct 23 '17 at 14:38
see this link: https://gis.stackexchange.com/questions/259369/multi-field-labelling-of-a-shape-file-with-pyqgis – ennine Oct 23 '17 at 19:11
@ennine - Did you see my edit and test the two lines of code I added? I don't see them in the question you posted :) – Joseph Oct 24 '17 at 09:04
Unfortunatly, I tried the two last lines of the code, but it did not work – ennine Oct 24 '17 at 13:48
1

@ennine - This worked for me previously on QGIS 2.18.2. I recently updated to 2.18.13 and now it doesn't work. I wonder if this is a bug... – Joseph Oct 24 '17 at 14:22
I tried QGIS LTR 2.14.19 with no result. – ennine Oct 24 '17 at 19:43

Multi-line labeling of a shapefile layer with pyQGis

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