Why is b.pop(0) over 200 times slower than del b[0] for bytearray?

The reason that b.pop(0) is slower than del b[0] for a bytearray is due to the implementation differences between the two methods.

In Python, when you use the del statement to remove an item from a list, the underlying array that stores the items are resized, but the memory previously used by the removed item is not immediately freed. This optimization helps make the del operation fast for lists since the memory can be reused later.

On the other hand, the pop the method returns the item that was removed from the list, and to do so, it needs to allocate a new object to store the removed item. This allocation takes time, especially for larger lists, which makes b.pop(0) it slower than del b[0].

Read More: What are Bits and Bytes

For a bytearray, the difference in performance between the two methods is even greater, because the memory management for bytearray is more complex than for lists. When you perform a pop operation on a bytearray, not only does Python need to allocate a new object to store the removed item, but it also needs to copy the remaining bytes in the bytearray to fill the gap left by the removed item. This makes the b.pop(0) operation over 200 times slower than del b[0] for bytearray objects.

So, if you need to remove items from the beginning of a bytearray and don’t need to preserve the removed items; it is generally faster to use the del a statement rather than the pop method.

Here’s a code example that demonstrates why b.pop(0) is slower than del b[0] for bytearray objects:

import time

# Create a large bytearray
b = bytearray(b'a' * 10**6)

# Measure the time it takes to perform 10^5 pop(0) operations
start = time.time()
for i in range(10**5):
    b.pop(0)
end = time.time()
print("Time taken by pop(0):", end - start)

# Re-create the bytearray
b = bytearray(b'a' * 10**6)

# Measure the time it takes to perform 10^5 del operations
start = time.time()
for i in range(10**5):
    del b[0]
end = time.time()
print("Time taken by del:", end - start)