Saturday, September 19, 2020

Python File Handling - Binary File

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Content:

Introduction:

Binary files handle data in the form of bytes. Hence, they can be used to read or write text, images or audio and video files. To open a binary files for reading purpose, we can user 'rb' mode. Here, 'b' is attached to 'r' to represent that its is a binary files. Similarly to write bytes into a binary file, we can use 'wb' mode. To read bytes from a binary file, we can use the read() method and to write bytes into a binary file, we can use the write() method

Example of Binary Files:

  • Document files: .pdf, .doc, .xls etc.
  • Image files: .png, .jpg, .gif, .bmp etc.
  • Video files: .mp4, .3gp, .mkv, .avi etc.
  • Audio files: .mp3, .wav, .mka, .aac etc.
  • Database files: .mdb, .accde, .frm, .sqlite etc.
  • Archive files: .zip, .rar, .iso, .7z etc.
  • Executable files: .exe, .dll, .class etc.

Opening and Closing binary files:

A binary can be opened by using the open() function, providing suitable mode argument in the function.

A binary file can be closed using the close() function. Once the operation on the file is complete then the file must be closed as it will ensure

In [5]:
# A python program to copy an image file into another file
In [6]:
file1 = open("cat1.jpg","rb")
file2=open("cat2.jpg","wb")
data=file1.read()
file2.write(data)
file1.close()
file2.close()

Binary file opening modes: The mode in the open function syntax will tell Python as what operation you want to do on a file

  • ‘wb’ – Open a file for write only mode in the binary format.
  • ‘rb’ – Open a file for the read-only mode in the binary format.
  • ‘ab’ – Open a file for appending only mode in the binary format.
  • ‘rb+’ – Open a file for read and write only mode in the binary format.
  • ‘ab+’ – Open a file for appending and read-only mode in the binary format.

Pickle in python:

Pickle or serialization is a process of converting a class object into a byte stream so that it can be stored in a file. This method help in storing structured data ina file like employee details like employee identification number(int type), name(string type) and salary(float type) in a file

Two important function of pickle module:

  • pickle.dump(object, file): This function is used to store the 'object' into the binary 'file'.pickling is done using the dump() function
  • pickel.load(file): The load function reads an object from a binary 'file' and returns it into 'object'.unpickling is done with the help of load() function

In [7]:
# A python program to store the data of employee(id, name, salary) in a binary file
In [8]:
import pickle
# employee class
class emp:
    def __init__(self, id,name,sal):
        self.id=id
        self.name=name
        self.sal=sal
    def display(self):
        print(self.id," ",self.name," ",self.sal)
        
f=open("emp.data",'wb')
n=int(input("Enter the number of employee"))
for i in range(n):
    id=int(input("Enter the id: "))
    name=input("Enter employee name: ")
    sal=float(input("Enter employee salary"))
    e=emp(id,name,sal)
    pickle.dump(e,f)
f.close()

Enter the number of employee2
Enter the id: 1
Enter employee name: james
Enter employee salary45000
Enter the id: 2
Enter employee name: harry
Enter employee salary55000

In [9]:
# Python program to read the data(unpickle) of emp file and display it
In [16]:
import pickle
f=open("emp.data","rb")
print("Employee Details")
while True:
    try:
        obj=pickle.load(f)
        obj.display()
    except EOFError:
            print('Thats it ......')
            break

f.close()

Employee Details
1   james   45000.0
2   harry   55000.0
Thats it ......

Practice Question:

  1. Write a python program to create a binary file and store the following records:

    roll(int type)
    name(string type)
    percentage(float type)
    grade(string type)

Note : take 4 value for the records from the user </p>

References:

  • Core python programming - Dr. R. Nageswara Rao
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