Write Binary File in Python

Use bytearray() Function

To write a binary file in Python:

• Use the bytearray() function to convert the list of bytes to a bytearray type object.
• Use a with clause with open() the method in write binary mode(wb)
• Use write() method to write the byte_array to the file.

We created a byte_list using a sequence of values from 0 to 255 in binary form.

The bytearray() function is a built-in function in Python that takes an iterable to convert it into an array of bytes.It is an object constructor for a mutable array of bytes, like a list, but unordered. From an iterable of integers, it only accepts values in the range(256), or the function throws a ValueError: byte must be in range(0, 256).

We used the bytearray() function to convert the byte_list to the byte_array. To successfully write the byte_array to the file, we used Python’s try-except control flow statement. It handles errors and exceptions without disrupting the flow of the program.

We used the with keyword to wrap the code block of writing the byte_array to the bytes_array.txt file. Next, we used the open() function to open a file for reading, or writing is a built-in function in Python. It took two arguments: the filename and the mode.

The mode is an optional argument. It defaults to r (read) if it’s not specified. We specified the mode as wb to create or truncate the existing file named bytes_array.txt as binary. The write() function wrote the byte_array to the bytes_array.txt file.

Use bytes() Function

To write a binary file in Python:

• Use the bytes() function to convert the list of bytes to a bytes type object.
• Use a with clause with open() the method in write binary mode(wb)
• Use write() method to write the byte_array to the file.

We have already discussed the creation of the byte_list, try-except clause, with keyword, and open() and write() functions while explaining the code snippet using the bytearray() function.

In this section, we used the bytes() function, similar to the bytearray() function but returned an immutable sequence of bytes type. We used this function to convert a byte_list to a byte_array. Once we got the byte_array, we used the write() function to write the byte_array to the bytes_array.txt file.

Use struct.pack() Function

To write a binary file in Python:

• Use the struct.pack() function to convert the list of bytes to a bytes type object.
• Use a with clause with open() the method in write binary mode(wb)
• Use write() method to write the byte_array to the file.

After successfully creating the byte_list, we imported the struct library.

Python’s struct module is a collection of functions that are used with binary data to perform operations such as packing, unpacking, and analyzing the contents of structs like C-structure formats. We imported it to process the byte_list.

The library provides the struct.pack() function that converts regular Python data types into packed binary data. It holds two arguments, as listed below.

• fmt – specifies the format in which the objects are to be packed.
• vals – contains any number of parameters needed to create the binary representation required for each element specified in the fmt parameter.

We used the 4B format to convert the byte_list into packed byte_array of the bytes data type. We used try-except blocks to handle the errors properly. Finally, we used the open() and write() functions to open the file and write the array to the byte_array.txt file.

Further reading:

Write to Text File in Python

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Write List to File in Python

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Use encode() Function with join()

To write a binary file in Python:

• Use the join() function to combine list elements as char.
• Use the encode() function to convert the string of bytes to a bytes type object.
• Use a with clause with open() the method in write binary mode(wb)
• Use write() method to write the byte_array to the file.

The join() function in Python is a built-in method that combines multiple strings into one string. It takes an iterable object as an argument and returns a single string formed from the elements of the iterable object separated by a separator character(s). We used the join() function to join the elements of byte_list as char.

The encode() function represents data in an alternative form. It converts information from one format to another, such as text to binary or vice versa. The purpose of encoding is to make the data more secure and easier to access and store.

We applied the encode() function on byte_array to convert it into a bytes type object and then wrote the array to the file using the open() and write() functions wrapped under the with statement.

Use to_bytes() Function

To write a binary file in Python:

• Use with keyword with the open() function to open the file.
• Use the for loop to iterate every element in the list of bytes.
• Use the to_bytes() function on every element to convert it to a byte.
• Use the write() function to write the byte to the file.

We created the byte_list of integers in the range(0-255). Then, after opening the file using the open() function, we used the for loop to iterate every element of byte_list.

Python’s to_bytes() function provides a convenient way to convert various built-in data types, such as integers, into an equivalent representation in bytes of specified size. It enables the user to easily store or manipulate data represented as a sequence of bytes. The function holds arguments:

• The length to ensure that the result has enough bytes to represent the number without data loss.
• The byteorder specifies an endian encoding that represents the integer.

We applied the to_bytes() function over every element of byte_list and wrote the returned byte to the file.