finally — Expert Examples

Block that always executes after try/except, used for cleanup

finally bytecode

How finally is compiled in CPython.

python

import dis

def try_finally():
    try:
        x = 1
    finally:
        y = 2

def full_pattern():
    try:
        x = 1
    except ValueError:
        x = 2
    else:
        x = 3
    finally:
        x = 4

print("try/finally:")
dis.dis(try_finally)
print("\nfull pattern:")
dis.dis(full_pattern)

# The finally block is duplicated in the bytecode:
# once for the normal path and once for the exception path.
# This ensures it runs regardless of how the try exits.

CPython duplicates the finally block's bytecode into both the normal and exception paths. SETUP_FINALLY pushes an entry onto the block stack that the VM uses to find the cleanup code.

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