NCERT Solutions for Class 12 Computer Science Chapter 2 Python File Handling

 

 

 

 

1. open() — The open() method opens the given file in the given mode and associates it with a file handle. Its syntax is file_object = open(file_name, access_mode).

2. read() — The read() method is used to read data from a file object. It reads at most 'n' bytes from the file, where 'n' is an optional parameter. If no 'n' is specified, the read() method reads the entire contents of the file. Its syntax is: file_object.read(n).

3. seek() — This method is used to position the file object at a particular position in a file. Its syntax is: file_object.seek(offset [, reference_point]).

4. dump() — This method is used to convert (pickling) Python objects for writing data in a binary file. Its syntax is : dump(data_object, file_object).

 

i. File Mode: 'r+'

fh = open("example.txt", "r+")

ii. File Mode: 'wb'

fh = open("bfile.dat", "wb")

iii. File Mode: 'a+'

fh = open("try.txt", "a+")

iv. File Mode: 'rb'

fh = open("btry.dat", "rb")

 

It is a good practice to close a file once we are done with the read and write operations. When we close a file, the system frees the memory allocated to it. Python ensures that any unwritten or unsaved data is flushed (written) to the file before it is closed. Therefore, it is always advised to close the file once our work is done. If we do not close file explicitly it will close automatically later when it's no longer in use or when the program terminates, without displaying any error message.

The code given in (a) will open file "practice.txt" in read mode and will read 10 bytes from it. Also, it will not close the file explicitly. On the other hand, the code given in (b) will open file "practice.txt" in read mode and will read the entire content of the file. Furthermore, it will automatically close the file after executing the code due to the with clause.

 

file = open("hello.txt", "a")

lines = [

    "Welcome my class\n",

    "It is a fun place\n",

    "You will learn and play"

]

file.writelines(lines)

file.close()

 

f = open("hello.txt", "r")

st = " "

while st:

    st = f.readlines()

    print(st)

f.close()

If the file "hello.txt" was opened in write mode instead of append mode, it would have overwritten the existing content of the file. In write mode ("w"), opening the file truncates its content if it already exists and starts writing from the beginning. Therefore, the previous contents of the file would have been replaced with the new lines provided in the write mode code snippet.

 

f = open("new.txt", "w")

while True:

    st = input("Enter next line:")

    if st == "END":

        break

    f.write(st + '\n')

f.close()

 

f = open("new.txt", "r")

while True:

    st = f.readline()

    if not st:

        break

    if st[0].isupper():

        print(st)

f.close()

Output

Enter next line:Hello world

Enter next line:welcome to     

Enter next line:Python programming

Enter next line:END

Hello world

Python programming

 

The pickling process serializes objects and converts them into a byte stream so that they can be stored in binary files.

Serialization is the process of transforming data or an object in memory (RAM) into a stream of bytes called byte streams. These byte streams, in a binary file, can then be stored on a disk, in a database, or sent through a network. The serialization process is also called pickling. Deserialization or unpickling is the inverse of the pickling process, where a byte stream is converted back into a Python object.

 

import pickle

 

with open("item.dat", 'wb') as itemfile:

    n = int(input("How many records to be entered? "))

    for i in range(n):

        ino = int(input("Enter item no: "))

        iname = input("Enter item name: ")

        qty = int(input("Enter quantity: "))

        price = float(input("Enter price: "))

        item = {"Item no": ino, "Item Name": iname, "Qty": qty, "Price": price}

        pickle.dump(item, itemfile)

    print("Successfully written item data")

with open("item.dat", "rb") as file:

    try:

        while True:

            item = pickle.load(file)

            print("\nItem No:", item["Item no"])

            print("Item Name:", item["Item Name"])

            print("Quantity:", item["Qty"])

            print("Price per item:", item["Price"])

            print("Amount:", item["Qty"] * item["Price"])

    except EOFError:

        pass 

Output

How many records to be entered? 5

Enter item no: 11

Enter item name: Mobile

Enter quantity: 4

Enter price: 20000

Enter item no: 12

Enter item name: Laptop

Enter quantity: 2

Enter price: 35000

Enter item no: 13

Enter item name: Computer

Enter quantity: 1

Enter price: 50000

Enter item no: 14

Enter item name: Television

Enter quantity: 4

Enter price: 25000 

Item No: 11

Item Name: Mobile

Quantity: 4

Price per item: 20000.0

Amount: 80000.0

Item No: 12

Item Name: Laptop

Quantity: 2

Price per item: 35000.0

Amount: 70000.0

Item No: 13

Item Name: Computer

Quantity: 1

Price per item: 50000.0

Amount: 50000.0

Item No: 14

Item Name: Television

Quantity: 4

Price per item: 25000.0

Amount: 100000.0