Calculate AGE in years

[Kessie1971]

I try this

class Student(persoon):
  StudentNr = 0
  def __init__(self, naam, sekse, geboortedatum):
    super().__init__(naam, sekse, geboortedatum)
      Student.StudentNr += 1
      self.StudentNr = Student.StudentNr

Error:
3.4.4 (v3.4.4:737efcadf5a6, Dec 20 2015, 20:20:57) [MSC v.1600 64 bit (AMD64)]
Python Type "help", "copyright", "credits" or "license" for more information.
[evaluate Objectgeoriënteerd programmeren_FeedbackVraag6.py]
Traceback (most recent call last):
  File "C:\Python\Objectgeoriënteerd programmeren_FeedbackVraag6.py", line 65, in <module>
    Student.StudentNr += 1
builtins.IndentationError: unexpected indent (x-wingide-python-shell://86941368/2, line 65)