Question

This module is part of a simple todo app I made with Python…

def deleteitem():
             showlist()
             get_item = int(raw_input( "\n Enter number of item to delete: \n"))
             f = open('todo.txt')
             lines = f.readlines()
             f.close()
             lines[get_item] = ""
             f = open('todo.txt','w')
             f.writelines(lines)
             f.close()
             showlist()

The number of lines in f obviously changes as items are added to the list… Problem here is that for example if a user enters ’10’ when there are only 9 lines in the file ( or anything else not in range) , it exits as expected with :

IndexError: list assignment index out of range

What can I add to the module so as to have it prompt user to enter an item within the range? I am assuming maybe a Try block … Or is there a way to catch an exception.. I am guessing there is an easy way to do this…

Answer 1

Judicious changes to your current code:

def deleteitem():
  showlist()

  with open("todo.txt") as f:
    lines = f.readlines()
  if len(lines) == 0:  # completely empty file
    return  # handle appropriately
  prompt = "Enter number to delete (1-%d), or 0 to abort: " % len(lines)
  while True:
    input = raw_input(prompt)
    try:
      input = int(input, 10)
    except ValueError:
      print "Invalid input."
    else:
      if 0 <= input <= len(lines):
        break
      print "Input out of range."
  if input == 0:
    return
  input -= 1  # adjust from [1,len] to [0,len)

  #del lines[input]  # if you want to remove that line completely
  lines[input] = "\n"  # or just make that line blank (what you had)

  with open("todo.txt", "w") as f:
    f.writelines(lines)

  showlist()