File Handling in Python — NCERT Solutions

A binary file opened in read only mode uses the mode rb.

Statement:

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

It is advised to close a file after reading or writing because Python then frees the memory/resources allocated to it, and any unwritten data is flushed to the file before closing.

If we do not close it, the data may remain in the buffer and may not be properly written immediately. However, the chapter says Python ensures unwritten data is flushed when closed, and it also notes that if the file object is reassigned, the previous file is automatically closed. The chapter does not say that a specific error message will be flashed just because the file is not closed.

• In (a), P.read(10) reads only 10 bytes/characters from practice.txt.
• In (b), the file is opened using a with clause, and x = P.read() reads the entire file. Also, the file is closed automatically when the with block ends.

So, the main differences are the amount of data read and automatic closing in the with statement.

In this code:

P = open("practice.txt", "r")
P.read(10)

• the file is opened in read mode,
• read(10) reads only the first 10 bytes/characters from the file.

So it does not read the whole file, only a limited part.

In this code:

with open("practice.txt", "r") as P:
    x = P.read()

• the file is opened in read mode,
• read() reads the entire contents of the file,
• and the file is closed automatically after the with block ends.

Use write() in append mode and end each line with \n:

f = open("hello.txt", "a")
f.write("Welcome my class\n")
f.write("It is a fun place\n")
f.write("You will learn and play\n")
f.close()

Each call writes one string to the file, and \n moves the next line to a new line.

A program to open hello.txt in read mode and display its contents:

f = open("hello.txt", "r")
print(f.read())
f.close()

If the file were opened in write mode instead of append mode, the previous contents would be erased/overwritten, because w creates a new empty file if needed or overwrites an existing one.

f = open("sentences.txt", "w")
while True:
    s = input("Enter sentence (END to stop): ")
    if s == "END":
        break
    f.write(s + "\n")
f.close()

f = open("sentences.txt", "r")
for line in f:
    if line and line[0].isupper():
        print(line, end="")
f.close()

This saves the sentences in a text file and then displays only those sentences whose first character is an uppercase alphabet.

Pickling is the process of converting a Python object into a byte stream so that it can be stored in a binary file.

• Serialization: transforming an object in memory (RAM) into a byte stream. This is also called pickling.
• De-serialization: converting the byte stream back into a Python object. This is also called unpickling.

import pickle

# writing records
n = int(input("Enter number of records: "))
file = open("item.dat", "wb")

for i in range(n):
    print("Record", i + 1)
    ino = int(input("Item No: "))
    iname = input("Item Name: ")
    qty = int(input("Qty: "))
    price = float(input("Price: "))
    rec = [ino, iname, qty, price]
    pickle.dump(rec, file)

file.close()

# reading records
print("\nDISPLAYING RECORDS")
file = open("item.dat", "rb")

try:
    while True:
        rec = pickle.load(file)
        ino, iname, qty, price = rec
        amount = price * qty
        print("Item No:", ino)
        print("Item Name:", iname)
        print("Quantity:", qty)
        print("Price per item:", price)
        print("Amount:", amount)
        print()
except EOFError:
    pass

file.close()

The records are stored as a list in a binary file using pickle.dump(), and read back using pickle.load(). The amount is calculated as $price \times qty$ while displaying.