I need to count how many times I executed a Pyhthon script in QGIS and I would like to do so by using a project variable as counter. However, I can only create them as string, thus I can't perform mathematical operations with them (count = count + 1).

Is it possible to change their type to integer or to create a counter using pygqis?

2 Answers 2

prj = QgsProject.instance()

The first line finds the current project (needed for QGIS >= 3). The next line initializes to zero, the last 2 lines read and set the counter incremented by one.

  • Written at same time as @Spacedman 's answer - he's focusing on the str/int conversion, the above adds the PyQGIS variable part.
    – Houska
    Jun 24, 2019 at 16:05
  • It worked! Thank you. Jun 24, 2019 at 16:07
  • I'd assumed the poster knew how to create string project variables, and I used an explicit str conversion instead of what I suspect is a coercion somewhere to string in your last line. But yay it works!
    – Spacedman
    Jun 24, 2019 at 17:37

Convert between strings and integers with str and int:

>>> x = "1"
>>> str(int(x) + 1)

So you'll be storing the string representation of your count as a string. Convert back to int when you retrieve it, and convert back to string when you store it.

Beware of errors if converting non-valid strings to ints:

>>> int("s")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ValueError: invalid literal for int() with base 10: 's'
  • Actually I faced the error you mentioned, but @Houska answer helped me. Thank you for your time. Jun 24, 2019 at 16:06

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