The Python Apprentice

Moment of zen

Figure 9.1: Beautiful is better than ugly

The with-block syntax looks like this:

with EXPR as VAR:    BLOCK

This is so-called syntactic sugar for a much more complex arrangement of try...except and try...finally blocks:

mgr = (EXPR)exit = type(mgr).__exit__  # Not calling it yetvalue = type(mgr).__enter__(mgr)exc = Truetry:    try:        VAR = value  # Only if "as VAR" is present        BLOCK    except:        # The exceptional case is handled here        exc = False        if not exit(mgr, *sys.exc_info()):            raise        # The exception is swallowed if exit() returns truefinally:    # The normal and non-local-goto cases are handled here    if exc:        exit(mgr, None, None, None)

Which ...