Python (3) readline returns empty string regardless of what is in the file

Question

I have a Python (3) program that reads some data in from a file, gets the relevant parts and spits it out to various other places. The problem is that `file.readline()` has started refusing to get any lines from any file. It just returns an empty string as if it was at the end of the file. The files are not the problem, I checked that with a quick script (read file, print line by line). The possible solution (although I don't know why) is I used 2to3 to convert the code to python3, but looking at the diff it printed I don't see any modifications to the file I/O stuff. Here is the program: ``` import threading import time def runFile(eventFile, channelRefFileName, serialPorts, timeScale, maxPEs): timer0 = threading.Timer(.0001, turnOffLED, [0, 0, 0, 1]) numEvents = getNumEvents(eventFile) eventCount = 0 while 1: linein = eventFile.readline() #if linein == '' or '
' or '
' or '': break #above checks if the end of file has been reached, below is debugging if linein == '': print('EO…

Accepted Answer

`getNumEvents` consumes the entire file, so when you go around reading it, its pointer is already at the end. Instead, reset the file pointer with `seek`, like this:

```
def runFile(eventFile, channelRefFileName, serialPorts, timeScale, maxPEs):
    timer0 = threading.Timer(.0001, turnOffLED, [0, 0, 0, 1])
    numEvents = getNumEvents(eventFile)
    eventFile.seek(0, 0)
    eventCount = 0
    for linein in eventFile:
        if linein == '': print('EOF')
        ....
```

Python (3) readline returns empty string regardless of what is in the file

Solution

Problem