如何从文本文件中打印字符串，在 Python 中以新行分隔

Question

I'm new in Python and i'm challenging myself by making an online library management with prompt for the 1st phase.I'm stacked in search function.I have found how to print a user's input,but i can't find how to print and the following data.I want to search a book by name.If book's name is in the text,i want to print the details of the book,like author,isbn etc.

Here is the following code i have made:

 def search():
    search_book = input('Search a book: ')

    with open('library.txt', mode='r', encoding='utf-8') as f:
        index = 0
        for line in f:
            index += 1
            if search_book in line:
                print(f'{search_book} is in line {index}')
                for details in range(index,index+5):
                    print(line[details])

And this is the text file's data:

FIRST
ME 
9781234
2000
Science

SECOND
YOU
9791234
1980
Literature

It is separated by new line.As example a user input the name FIRST and the result will be:

FIRST
ME 
9781234
2000
Science

Answer 1

There are two file options we can consider,

1. Csv file - Instead of individual readline, you could use one line for one book entry.

   # ---------test.csv -------------
   # BookName, ItemCode, Price 
   # Book1, 00012, 14.55
   # Book2, 00232, 55.12
   # -----End Csv-------------------
   import csv 
   def read_csv(filename:str):
      file_contents = None
      # reading csv file 
      with open(filename, 'r') as csvfile: 
         file_contents = csv.reader(csvfile)
      return file_contents
    
    def search(file_contents, book_name:str):
       if not file_contents:
         return None
       for line in file_contents:
         if book_name in line: 
            return line
    
     if __name__ == '__main__':
       file_contents = read_csv('test.csv')
       line = search(file_contents, 'ME')
       print(line if line else 'No Hit Found')

2. Json - This is much better option than csv file

import json
def read_json(filename:str) -> dict:
   with open(filename) as json_file:
      all_books = json.load(json_file)
   return all_books

 def search(all_books:dict, book_name:str):
   for book_id, book_details in all_books.items():
      if book_details['Name'] == book_name:
         return book_details
   return None
 
 if __name__ == '__main__':
    all_books = read_json('books.json')
    book = search(all_books, 'YOU')
    print(book if book else 'Not hit found')

If your file contents can't change, then I will go with @tripleee suggestion above. Good luck.

Answer 2

You are reading a line at a time, and looping over the first line's contents. At this point in the program, there are not yet any additional lines. But a fix is relatively easy:

def search():
    search_book = input('Search a book: ')

    with open('library.txt', mode='r', encoding='utf-8') as f:
        index = 0
        print_this_many = 0
        for line in f:
            index += 1
            if search_book in line:
                print(f'{search_book} is in line {index}')
                print_this_many = 5
            if print_this_many:
                print(line, end='')
                print_this_many -= 1

We don't have the next lines in memory yet, but we can remember how many of them to print as we go ahead and read more of them. The print_this_many variable is used for this: When we see the title we want, we set it to 5 (to specify that this and the next four lines should be printed). Now, each time we read a new line, we check if this variable is positive; if it is, we print the line and decrement the variable. When it reaches zero, we will no longer print the following lines. This allows us to "remember" across iterations of the for loop which reads each new line whether we are in the middle of printing something.

A much better solution is to read the database into memory once, and organize the lines into a dictionary, for example.

def read_lib(filename):
    library = dict()
    with open(filename) as lib:
        title = None
        info = []
        for line in lib:
            line = line.rstrip('\n')
            if title is None:
                title = line
            elif line == '':
                if title and info:
                    library[title] = info
                title = None
            else:
                info.append(line)


def search(title, library):
    if title in library:
        return library[title]
    else:
        return None

def main():
    my_library = read_lib('library.txt')
    while True:
        sought = input('Search a book: ')
        found = search(sought, my_library)
        if found:
            print('\n'.join(found))
        else:
            print('Sorry, no such title in library')