如何将内容传递给python中的类的实例

Question

I have a class Book, and this basically only returns the content for now, but i have an external file that i need to read, and then pass the content into that instance, for instance i start declaring the book instance as b1

class Book():
    def __init__(self,poem="empty"):
        self.poem = poem

    def __str__(self):
        return self.poem

def reading(instance, file_content):
    list_of_content = []
    with open(file_content, "r") as f:
        for i in f:
            list_of_content.append(i.split())
    flatten = [item for sublist in list_of_content for item in sublist]
    string = " ".join(flatten) 
    instance = Book(string)
    return instance


b1 = Book() # book has a default value so it wont make any error
reading(b1, "file.txt")
print("File contains:",b1) # prints empty, because reading function has not passed any data i think

The problem is that now it does print always only "empty", how can i pass the data that i read from the file to the instance that is called at reading(), this is for learning purpose.

Answer 1

class Book():
    def __init__(self,poem="empty"):
        self.poem = poem

    def __str__(self):
        return self.poem

def reading(self, file_content):
    list_of_content = []
    with open(file_content, "r") as f:
        for i in f:
            list_of_content.append(i.split())
    flatten = [item for sublist in list_of_content for item in sublist]
    string = " ".join(flatten)
    self.poem=string


b1 = Book() 
reading(b1, "file.txt")
print("File contains:",b1)

Output

File contains: I really love christmas Keep the change ya filthy animal Pizza is my fav food Did someone say peanut butter?

Answer 2

For creating instances with some additional functionality for instance often used classmethods https://www.programiz.com/python-programming/methods/built-in/classmethod

Try this one:

class Book():
def __init__(self,poem="empty"):
    self.poem = poem

@classmethod
def load_book(cls, filename):
    list_of_content = []
    with open(filename, "r") as input_file:
        for line in input_file:
            list_of_content.append(line.split())
        flatten = [item for sublist in list_of_content for item in sublist]
        string = " ".join(flatten) 
        book_inst = cls(string)
        return book_inst

def __str__(self):
    return self.poem


book = Book.load_book("input.txt")
print(book)

Answer 3

reading should be a method of the class, but you could also just initialize Book when created:

class Book():

    def __init__(self,filename):
        list_of_content = []
        with open(filename) as f:
            for line in f:
                list_of_content.append(line.split())
        flatten = [item for sublist in list_of_content for item in sublist]
        string = " ".join(flatten) 
        self.poem = string

    def __str__(self):
        return self.poem

b1 = Book('file.txt')
print("File contains:",b1)

If you still want to create empty books and possibly read different files into the same Book , make read a method:

class Book():
    def __init__(self,poem='<empty>'):
        self.poem = poem

    def read(self,filename):        
        list_of_content = []
        with open(filename) as f:
            for line in f:
                list_of_content.append(line.split())
        flatten = [item for sublist in list_of_content for item in sublist]
        string = " ".join(flatten) 
        self.poem = string

    def __str__(self):
        return self.poem

b1 = Book()
print("File contains:",b1)
b1.read('file.txt')
print("File now contains:",b1)