Question

Write a program that allows the user to navigate the lines of text in a file. The program should prompt the user for a filename and input the lines of text into a list. The program then enters a loop in which it prints the number of lines in the file and prompts the user for a line number. Actual line numbers range from 1 to the number of lines in the file. If the input is 0, the program quits. Otherwise, the program prints the line associated with that number.

An example file and the program input and output is shown below:

example.txt

Line 1.
Line 2.
Line 3.

Enter the input file name: example.txt

The file has 3 lines.
Enter a line number [0 to quit]: 2
2 :  Line 2.
The file has 3 lines.
Enter a line number [0 to quit]: 4
ERROR: line number must be less than 3.
The file has 3 lines.
Enter a line number [0 to quit]: 0

Make sure the program gracefully handles a user entering a line number that is too high.

Answer 1

filename = input("Enter file name: ")

try:

    f = open(filename, "r")

    lines = f.readlines()

    while True:

        print("The file has", len(lines), "lines.")

        number = int(input("Enter a line number [0 to quit]: "))

        if number == 0:

            break

        if 1 <= number <= len(lines):

            print(number, ':', lines[number-1].strip())

        else:

            print("ERROR: line number must be less than", len(lines))

    f.close()

except IOError:

    print(filename + " does not exists!")