attfile=csv.reader(file,delimiter=",") returns an object of the type <class '_csv.reader'>.
This is a generator. So if you read the csv file using csv.reader it does not reset/seek to beginning in the new iteration.
Capture the row in a list. Add the following to your code.
with open('attendance.csv') as file:
attfile=csv.reader(file,delimiter=",")
attendance_data = list(attfile)
.
.
.
for rollno in SeriesRollNo:
for row in attendance_data:
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