debug print shortcut?

[Jeff Epler]

Here's one way.  You specify the expression as a string, and the value
or the exception raised is printed.

import sys

def debug(expression, depth=1):
    frame = sys._getframe(depth)
    locals = frame.f_locals
    globals = frame.f_globals
    try:
        value = eval(expression, globals, locals)
    except:
        value = sys.exc_info()[1]
    print >>sys.stderr, "%r -> %r" % (expression, value)

>>> debug("3+3")
'3+3' -> 6
>>> debug("1/0")
'1/0' -> <exceptions.ZeroDivisionError instance at 0x00B6E248>
>>> def f():
...     y = 3
...     debug("y+1")
...
>>> f()
'y+1' -> 4

Another way would be to pass the result of the expression to debug(),
and use inspect.getsource() to locate the line of code in the caller.  I
haven't written this, but usage might look like
>>> debug(3+3)
debug(3+3) -> 6

With this approach, exceptions would be propagated, not handled in
debug().

Jeff
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