Combining finally and except by Nesting

Prior to Python 2.5, it is actually possible to combine finally and except clauses in a try by syntactically nesting a try/except in the try block of a try/finally statement (we’ll explore this technique more fully in Chapter 35). In fact, the following has the same effect as the new merged form shown at the start of this section:

try:                               # Nested equivalent to merged form
    try:
        main-action
    except Exception1:
        handler1
    except Exception2:
        handler2
    ...
    else:
        no-error
finally:
    cleanup

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Again, the finally block is always run on the way out, regardless of what happened in the main action and regardless of any exception handlers run in the nested try (trace through the four cases listed previously to see how this works the same). Since an else always requires an except, this nested form even sports the same mixing constraints of the unified statement form outlined in the preceding section.

However, this nested equivalent is more obscure and requires more code than the new merged form (one four-character line, at least). Mixing finally into the same statement makes your code easier to write and read, so this is the generally preferred technique today.