Inserting variable into layer name in PyQGIS?

Question

I want to insert current date into name of new layer. My current code to save layer with hardcoded name is like this:

_writer = QgsVectorFileWriter.writeAsVectorFormat(layer,r"D:\Maps\layer.shp","utf-8",None,"ESRI Shapefile")

I can get current date using:

cur_date_apndx = time.strftime("%d_%m_%Y") 

statement, but I can not insert cur_date_apndx into the code above. I think "r" in the 2nd parameter of writeAsVectorFormat is the reason. If I remove "r" layer is not saved.

Could anyone help?

Answer 1

I prefer just using forward slashes instead of using raw string coupled with backward slashes. But you could use the format() method to insert the date into the filename:

_writer = QgsVectorFileWriter.writeAsVectorFormat(layer, "D:/Maps/layer_{}.shp".format(cur_date_apndx),"utf-8",None,"ESRI Shapefile")

• mgri: 12 seconds between the two answers :)
• Joseph: @mgri - Indeed! And cur_date_apndx does come out as a string :)
• E Bobrov: @Joseph, perfect! But _writer = QgsVectorFileWriter.writeAsVectorFormat(layer, "D:/Maps/layer_{}.shp".format(cur_date_apndx),"utf-8",None,"ESRI Shapefile") doesn`t work and _writer = QgsVectorFileWriter.writeAsVectorFormat(layer, r"D:/Maps/layer_{}.shp".format(cur_date_apndx),"utf-8",None,"ESRI Shapefile") is working.
• Joseph: @EBobrov - Most welcome although mgri's answer is also correct (and he answered first) so perhaps accept his answer as both our solutions are essentially the same? ;)
• E Bobrov: @Joseph - I do not know why but mgri`s answer (without r) is not working. Previously I tried hardcoded layer name without variable and r method but unsuccessfully.

Answer 2

I can't test it right now, but if cur_date_apndx is a string, you may simply compose the output name in this way:

output_name = 'D:/Maps/layer_' + cur_date_apndx + '.shp'
_writer = QgsVectorFileWriter.writeAsVectorFormat(layer,output_name,"utf-8",None,"ESRI Shapefile")

otherwise, use str(cur_date_apndx) isntead of cur_date_apndx.

I used slashes (/) instead of backslashes (\) because your format time was "%d_%m_%Y" (but the method with r should however work).

• E Bobrov: Thank you! It is strange but statement without 'r' doesnt work. Ive commented it above.
• mgri: @EBobrov weird behavior, maybe I'm missing something. Did you try using double quotes?
• E Bobrov: yap, I tried to use double quotes.