删除外部文本文件中的某些行

Question

I'm working on a program which should be able to handle basic library tasks. I've a problem with a class method which is suppose to offer the user the possibility to remove a certain book from the library. The list of books is contained on an external textfile with the following format (author, title):

  Vibeke Olsson, Molnfri bombnatt 
  Axel Munthe, Boken om San Michele

The metod I'm using is shown below:

---

def removeBook(self):
    removal_of_book = input("What's the book's titel, author you'd like to remove?: ")
    with open("books1.txt" , "r+") as li:
        new_li = li.readlines()
        li.seek(0)
        for line in new_li:
            if removal_of_book not in line:
                li.write(line)
        li.truncate()
    print(removal_of_book + " is removed from the system!")

The problem with this method is it that every row containing removal_of_book gets removed (or not rewritten on the file). I know that the method is far from optimal and probably should be scratched but I'm completely lost in finding an alternative.

Does anyone have a better solution to this problem?

Answer 1

You can create your lines to write into the new file on the fly using a list comprehension and then write them to the new file afterwards (using the same file name to overwrite the original file):

def removeBook(self):

    to_remove = input("What's the book's title, author you'd like to remove?: ")

    with open("books1.txt" , "r+") as li:

        new_li = [line for line in li.readlines() if to_remove not in line]

    new_file = open('books1.txt', 'w'); new_file.write(new_li); new_file.close()

    print(to_remove + " is removed from the system!")

Note that string membership checking is case sensitive, so you are expecting your user to match your case in the original file exactly . You might think about converting the strings to lower-case prior to performing your check using lower() .