How can I raise an EOF error?

I am a newbie learning python. Please take a look at the below code (From Data Structures and Algorithms in Python by Goodrich, et al).

age = -1   # an initially invalid choice
while age <= 0:
    try:
        age = int(input('Enter your age in years: '))
        if age <= 0:
            print('Your age must be positive.')
    except ValueError:
        print('That is an invalid age specification.')
    except EOFError:
        print('There was an unexpected error reading input.')
        raise  # let's re-raise this exception.

I know what ValueError is. For example the ValueError occurs if the input is given as characters instead of an integer.

On the other hand, I have no idea when EOFError raises.

1. I can't get what 're-raise this exception' means

2. The book says, 'the call to input will raise an EOFError if the console input fails.' Again, I have no idea what console input is and when console input fails.

I have tried several ways of raising EOFError, but every time I tried there was only ValueError. Can someone give me some idea?

Thanks in advance.

From input's documentation:

When EOF is read, EOFError is raised.

EOF is sent when the input stream reaches the end, or if it's from the console, it means the user presses ctrl-D on *NIX, or ctrl-Z on Windows.

You can catch the EOFError exception and break your while loop as a way to end the program gracefully, so change your exception block to:

except EOFError:
    print('Done.')
    break