Python and RFID

Not sure, but can it be, that you execute the script multiple times in parallel and that two parallel writes are the root cause?

parallel writes could explain the behaviour you mention.
It could even explain loss of data.

If that would be the case file locking would solve the issue.

Make also sure, that you close the file immediately after having written to it.

Ideally you use file locking.
you collect the data and open the file only after having fetched the data it is also important, that you close the file immediately after your write.
Then you can unlock again.

from Tkinter import *
from sqlite3 import *
from tkFileDialog import askopenfilename, askdirectory
import re
from datetime import *

comma = ', '

classroom = 'testpi'
text_document = '/home/pi/ShareFile/event_tracker_data/testpi.txt'
#'/media/pi/VERBATIM/revised attendance/toilet.txt'

def tkinter_window():
    def read():
        csv_doc = open(text_document, "r")
        ## test
        print csv_doc.read()
        
    ##---- tkinter
    add_toilet_tkinter = Tk()
    add_toilet_tkinter.title('toilet movment')

    ## frames
    add_frame = Frame(add_toilet_tkinter)

    ## add
    add_entry = Entry(add_frame)
    add_entry.pack()

    print_file = Button(add_frame, text = 'read', command = lambda: read())
    print_file.pack()
    
    
    ##frame pack
    add_frame.pack()

    ## bind + mainloop
    def add_bind(event):
        global comma
        global classroom
        
        rfid = add_entry.get()
        
        #---- AutoFill the date, month, and year
        date_time = datetime.now()
        date_time_regax = "[0-9-:]+"
        all_date_time = re.findall(date_time_regax, str(date_time))
        
        time_for_db = all_date_time[1]
        date_for_db = all_date_time[0]

       
        csv_doc = open(text_document, "a")

        ##
        ## create the entry ('Rfid, first name, last name, name of place!)
        entry = classroom + comma + rfid + comma + comma + comma + comma + time_for_db + comma + date_for_db
        print entry
        csv_doc.write(entry + "\r\n")
        csv_doc.close()


        ## clear entry for new
        add_entry.delete(0, END)
        
    
    add_entry.focus() 
    add_toilet_tkinter.bind("<Return>", add_bind)
    add_toilet_tkinter.mainloop()


## start program

tkinter_window()
    
    

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What is happening is this:

Each entry should be on a new line and look like this:

0268340542, , , , 11:28:41, 2017-06-07

I get a lot like this and then it does the following:

026835201202683520560268339729026833971602683537820268339746026835368202683500370268351993026833974102683397410268350159026835013402683375290268350089026835203902683501050268350105, , , , 09:25:48, 2017-06-12

So instead of recording each RFID card it puts them all into the one line with one , , ,  , time and date at the end.

So would the above be a file locking problem and if so, what do I need to change in the code to fix it?