get_line.py

# Copyright 2020, Brigham Young University-Idaho. All rights reserved.

"""
This program asks the user for
1) the name of a text file
2) a line number
and prints the text from that line of the file.
"""
def main():
    try:
        # Get a filename from the user.
        filename = input("Enter the name of text file: ")

        # Read the text file specified by the user into a list.
        text_lines = read_list(filename)

        # Get a line number from the user.
        linenum = int(input("Enter a line number: "))

        # Get the line that the user requested from the list.
        line = text_lines[linenum - 1]

        # Print the line that the user requested.
        print()
        print(line)

    except FileNotFoundError as not_found_err:
        # This code will be executed if the user enters
        # the name of a file that doesn't exist.
        print()
        print(type(not_found_err).__name__, not_found_err, sep=": ")
        print(f"The file {filename} doesn't exist.")
        print("Run the program again and enter the" \
                " name of an existing file.")

    except ValueError as val_err:
        # This code will be executed if the user enters
        # an invalid integer for the line number.
        print()
        print(type(val_err).__name__, val_err, sep=": ")
        print("You entered an invalid integer for the line number.")
        print("Run the program again and enter an integer for" \
                " the line number.")

    except IndexError as index_err:
        # This code will be executed if the user enters a valid
        # integer for the line number, but the integer is greater
        # than the number of lines in the file.
        print()
        print(type(index_err).__name__, index_err, sep=": ")
        length = len(text_lines)
        if linenum < 0:
            print(f"{linenum} is a negative integer.")
        else:
            print(f"{linenum} is greater than the number" \
                    f" of lines in {filename}.")
            print(f"There are only {length} lines in {filename}.")
        print(f"Run the program again and enter a line number" \
                f" between 1 and {length}.")

    except Exception as excep:
        # This code will be executed if some
        # other type of exception occurs.
        print()
        print(type(excep).__name__, excep, sep=": ")


def read_list(filename):
    """Read the contents of a text file into a list
    and return the list that contains the lines of text.

    Parameter filename: the name of the text file to read
    Return: a list of strings
    """
    # Create an empty list named text_lines.
    text_lines = []

    # Open the text file for reading and store a reference
    # to the opened file in a variable named text_file.
    with open(filename, "rt") as text_file:

        # Read the contents of the text
        # file one line at a time.
        for line in text_file:

            # Remove white space, if there is any,
            # from the beginning and end of the line.
            clean_line = line.strip()

            # Append the clean line of text
            # onto the end of the list.
            text_lines.append(clean_line)

    # Return the list that contains the lines of text.
    return text_lines


# If this file was executed like this:
# > python teach_solution.py
# then call the main function. However, if this file
# was simply imported, then skip the call to main.
if __name__ == "__main__":
    main()