So I've written a simple program that allows user to enter a line they would like to edit and text they would like to put into that line

def edit_line(file):
    a_file = open(file, 'r')
    list_of_lines = a_file.readlines()
    list_of_lines[int(input('What line would you like to edit?: ')) - 1] = input('Write your text here: ')   '\n'

    a_file = open(file, 'w')
    a_file.writelines(list_of_lines)
    a_file.close()


edit_line('sample.txt')

When I run the program it works fine. However, It asks the user to input the text first and the line number second.

What is the reason for this and how can I fix it?

CodePudding user response：

If you want to fix the problem, just split the one line into two:

Instead of:

list_of_lines[int(input('What line would you like to edit?: ')) - 1] = input('Write your text here: ')   '\n'

Do:

 index = int(input('What line would you like to edit?: ')) - 1
 list_of_lines[index] = input('Write your text here: ')   '\n'

And as the answer @Guy linked explains, when you are doing an assignment line of code, the right hand (value of the variable) is run before the left side.

CodePudding user response：

Validation is everything! What would happen if the user's input for the line number wasn't within the range of lines read from the file?

Here's a more robust approach:

def edit_line(filename):
    with open(filename, 'r ') as file:
        lines = file.readlines()
        while True:
            try:
                lineno = int(input('What line would you like to edit: '))
                if 0 <= lineno < len(lines):
                    lines[lineno] = input('Write your text here: ')   '\n'
                    file.seek(0)
                    file.writelines(lines)
                    file.truncate()
                    break
                else:
                    raise ValueError('Line number out of range')
            except ValueError as e:
                print(e)

edit_line('edit.txt')