Creating a program that records speed in a speed trap

[astonavfc]

error traceback, sorted out the names just stuck with subtracting

Error:
Traceback (most recent call last):
  File "C:\Users\Aston Instone\Documents\College\IT BTEC\Unit 16\Assignment 2\Python Program\CurrentProgram.py", line 30, in <module>
    dateTimeIn-dateTimeOut
TypeError: unsupported operand type(s) for -: 'function' and 'function'

>>>

---

It tells me timestamp is needed so I enter it than says timestamp is not defined?

from datetime import datetime
#Function to convert date from string to dateTime
def dateTimeIn(timestamp):
    dateTimeIn = datetime.strptime(strTimeIn, "%d/%m/%Y %H:%M:%S")
    return dateTimeIn
def dateTimeOut(timestamp):
    dateTimeOut = datetime.strptime(strTimeOut, "%d/%m/%Y %H:%M:%S")
    return dateTimeOut
   

#Main Program   
myFileIn=open("CameraIn.txt","rt")
myFileOutput=open("Output.txt","rt")
for lineIn in myFileIn:
    lineIn=myFileIn.readline()
    theListIn=lineIn.split(",")
    regIn=theListIn[0]
    strTimeIn=theListIn[1]
    myFileOut=open("CameraOut.txt","rt")
    for lineOut in myFileOut:
        lineOut=myFileOut.readline()
        theListOut=lineOut.split(",")
        regOut=theListOut[0]
        strTimeOut=theListOut[1]
        if regIn==regOut:
            dateTimeIn(timestamp)-dateTimeOut(timestamp)

Error:
Traceback (most recent call last):
  File "C:\Users\Aston Instone\Documents\College\IT BTEC\Unit 16\Assignment 2\Python Program\CurrentProgram.py", line 30, in <module>
    dateTimeIn(timestamp)-dateTimeOut(timestamp)
NameError: name 'timestamp' is not defined

>>>

---

I have to get the timestamp from the file and I want it to do this for every timestamp that shows that the car is speeding?