Debugging with Outer try Statements

You can also make use of exception handlers to replace Python’s default top-level exception-handling behavior. By wrapping an entire program (or a call to it) in an outer try in your top-level code, you can catch any exception that may occur while your program runs, thereby subverting the default program termination.

In the following, the empty except clause catches any uncaught exception raised while the program runs. To get hold of the actual exception that occurred, fetch the sys.exc_info function call result from the built-in sys module; it returns a tuple whose first two items contain the current exception’s class and the instance object raised (more on sys.exc_info in a moment):

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try:
    ...run program...
except:                         # All uncaught exceptions come here
    import sys
    print('uncaught!', sys.exc_info()[0], sys.exc_info()[1])

This structure is commonly used during development, to keep programs active even after errors occur—it allows you to run additional tests without having to restart. It’s also used when testing other program code, as described in the next section.