Hey, I have a file: ;;;;;;;;;Eintrittsdatum;;; ;;;;;;;;;04.03.16;;10,00 €;genehmigt ;;;;;;;;;04.03.16;;10,00 €;genehmigt which I try to parse using def dateToNumpyDate(s): s = s.decode("utf-8") ret = datetime.datetime.strptime(s, "%d.%m.%y").isoformat() return ret def generateMembers(): members = np.genfromtxt("test_CSC_Mitglieder.csv", dtype = { "names" : ["EntryDate"], "formats" : ['datetime64[D]'] }, converters = { 9 : dateToNumpyDate }, skip_header = 1, delimiter = ";", usecols = (9)) count = members.shape[0] y = np.linspace(1, count, count) print(members) print(members.dtype) plt.plot(members["EntryDate"], y) plt.show() but the datatype was ignored homehow, <U19 instead of the datetime64 ['2016-03-04T00:00:00' '2016-03-04T00:00:00'] <U19 CSC.py:76: VisibleDeprecationWarning: using a non-integer number instead of an integer will result in an error in the future plt.plot(members["EntryDate"], y) Traceback (most recent call last): File "CSC.py", line 82, in <module> generateMembers() File "CSC.py", line 76, in generateMembers plt.plot(members["EntryDate"], y) IndexError: only integers, slices (`:`), ellipsis (`...`), numpy.newaxis (`None`) and integer or boolean arrays are valid indices I also tried to print the return of dateToNumpbyData: 2016-03-04T00:00:00 2016-03-04T00:00:00 2016-03-04T00:00:00 Is there a problem with the dtype argument? Thanks, Florian