What is the process used to convert an object to a stream of bytes that can be saved in a file Python?

Files are used in order to store data permanently. File handling is performing various operations (read, write, delete, update, etc.) on these files. In Python, file handling process takes place in the following steps:

1. Open file
2. Perform operation
3. Close file

There are four basic modes in which a file can be opened― read, write, append, and exclusive creations. In addition, Python allows you to specify two modes in which a file can be handled― binary and text. Binary mode is used for handling all kinds of non-text data like image files and executable files.

Python stores files in the form of bytes on the disk. So, when a file is opened in text mode, these files are decoded from bytes to return string objects. While files opened in binary mode return contents as bytes objects (sequences of single bytes) without any decoding. Let us see how to write bytes to a file in Python.

First, open a file in binary write mode and then specify the contents to write in the form of bytes. Next, use the write function to write the byte contents to a binary file. 

Python3

some_bytes = b'\xC3\xA9'

with open("my_file.txt", "wb") as binary_file:

    binary_file.write(some_bytes)

Output:

my_file.txt

In the above example, we opened a file in binary write mode and then wrote some bytes contents as bytes in the binary file.

Alternatively, open() and close() can be called explicitly as shown below. However, this method requires you to perform error handling yourself, that is, ensure that the file is always closed, even if there is an error during writing. So, using the “with” statementis better in this regard as it will automatically close the file when the block ends.

Python3

some_bytes = b'\x21'

binary_file = open("my_file.txt", "wb")

binary_file.write(some_bytes)

binary_file.close()

Output:

my_file.txt

Also, some_bytes can be in the form of bytearray which is mutable, or bytes object which is immutable as shown below.

Python3

byte_arr = [65,66,67,68] 

some_bytes = bytearray(byte_arr)

some_bytes.append(33)

immutable_bytes = bytes(some_bytes)

with open("my_file.txt", "wb") as binary_file:

    binary_file.write(immutable_bytes)

Output:

my_file.txt

Pickle, which is part of the Python library by default, is an important module whenever you need persistence between user sessions. As a module, pickle provides for the saving of Python objects between processes.

Whether you are programming for a database, game, forum, or some other application that must save information between sessions, pickle is useful for saving identifiers and settings. The pickle module can store things such as data types such as booleans, strings, and byte arrays, lists, dictionaries, functions, and more.

Note: The concept of pickling is also known as serialization, marshaling, and flattening. However, the point is always the same—to save an object to a file for later retrieval. Pickling accomplishes this by writing the object as one long stream of bytes. 

Pickle Example Code in Python

To write an object to a file, you use a code in the following syntax:

import pickle
object = Object()
filehandler = open(filename, 'w')
pickle.dump(object, filehandler)

Here's how a real-world example looks:

import pickle
import math
object_pi = math.pi
file_pi = open('filename_pi.obj', 'w')
pickle.dump(object_pi, file_pi)

This snippet writes the contents of object_pi to the file handler file_pi, which in turn is bound to the file filename_pi.obj in the directory of execution.

To restore the value of the object to memory, load the object from the file. Assuming that pickle has not yet been imported for use, start by importing it:

import pickle
filehandler = open(filename, 'r')
object = pickle.load(filehandler)

The following code restores the value of pi:

import pickle
file_pi2 = open('filename_pi.obj', 'r')
object_pi2 = pickle.load(file_pi2)

The object is then ready for use once again, this time as object_pi2. You can, of course, reuse the original names, if you prefer. This example uses distinct names for clarity.

Things to Remember About Pickle

Keep these things in mind when using the pickle module:

• The pickle protocol is specific to Python – it's not guaranteed to be cross-language compatible. You most likely cannot transfer the information to make it useful in Perl, PHP, Java, or other languages.
• There is also no guarantee of compatibility between different versions of Python. IThe incompatibility exists because not every Python data structure can be serialized by the module.
• By default, the latest version of the pickle protocol is used. It remains that way unless you manually change it.

Tip: Also find out how to use shelve to save objects in Python for another method of maintaining object continuity.

What built in Python module can be used to convert an object to a stream of bytes that can be saved in a file?

Is a process in which a byte stream is converted into an object?

Which method is used for object serialization in Python?

What is pickle used for in Python?