Try-except in while loop: error with closing program

[Lupin_III]

Hi, I have this code that includes a sort of watch dog within a try block inside a while loop
I don't understand two things:
1) why sometimes, not always, it is generated the error;
2) why, because of this error, the program get closed and exits instead of going ahead with the while loop
This simple script should run forever (while loop) and the file my_time.txt is a simple file where another python program write last time its code is executed.
This is the code that write the timestamp in my_time.txt every 15 seconds

import time
with open(my_time.txt,"w") as Time_check:
    Time_check.write(str(time.time()))

this is the code I need help

import time
while True:
        try:
            with open(my_time.txt,"r") as Time_check:
                print(Time_check.read())
                Time_value=float(Time_check.read()) #This line generates the error
            Delta_time = (time.time()-Time_value)
            if Delta_time > 30: #30 seconds
                do FOO
            else:
                do FOO_
        except:
            print (sys.exc_info()[0])
            print (sys.exc_info()[1])
            print (sys.exc_info()[2])

This is the error that sometimes get generated

Error:
<type 'exceptions.ValueError'>
could not convert string to float: 
<traceback object at 0x0000000003A70348>

Last time I got this error, the timestamp written inside the my_time.txt was 1593707454.53
Thanks a lot to all