Python memoryview() Function

The memoryview() function in Python provides a way to access the memory of a binary object (like bytes or bytearray) without copying the actual data. It's very useful for working with large data buffers efficiently.

Syntax

memoryview(obj)

Parameters:

• obj – A binary object that supports the buffer protocol, like bytes, bytearray, or array.array.

Returns:

• A memoryview object that references the same data without copying it.

Example: Using memoryview() with bytearray

data = bytearray("hello", "utf-8")
mv = memoryview(data)

print(mv[0])        # Output: 104 (ASCII of 'h')
mv[0] = 72          # Change 'h' to 'H'
print(data)         # Output: bytearray(b'Hello')

104
bytearray(b'Hello')

Why Use memoryview()?

• Efficient: No need to copy data
• Fast: Great for performance with large datasets
• Direct access: You can slice, read, or modify without unpacking

Example: Slicing Memory Efficiently

numbers = bytearray([10, 20, 30, 40, 50])
mv = memoryview(numbers)
slice_mv = mv[1:4]

print(list(slice_mv))

[20, 30, 40]

Converting Back to Bytes

mv = memoryview(b"data")
print(bytes(mv))

b'data'

Common Mistakes

• Using memoryview() on non-buffer objects like strings → will raise TypeError
• Trying to assign new values to a memoryview of bytes (which is immutable)

Interview Tip

In performance-sensitive applications (like image processing, network packets, or binary file handling), memoryview() helps reduce memory overhead.

Summary

• memoryview() gives you access to the internal data of a binary object.
• It is efficient because it avoids data copying.
• Supports slicing and modification (if the source is mutable).

Practice Problem

Create a bytearray from the word "data", convert it to a memoryview, change 'd' to 'D', and print the updated bytearray.

b = bytearray("data", "utf-8")
mv = memoryview(b)
mv[0] = ord("D")
print(b)

Expected Output:

bytearray(b'Data')