As a longtime Lisp observer, I can't say that I've ever seen Jon Harrop conduct himself as a "heavyweight" in forums unrelated to OCaml, Mathematica, or F#.
x = {}
def f():
print(x['foo'])
f()
# ...
Traceback (most recent call last):
File "stack.py", line 6, in <module>
f()
File "stack.py", line 4, in f
print(x['foo'])
KeyError: 'foo'
import sys
def short_err(exc_type, exc, tb):
sys.stderr.write("error: tracebacks too long\n")
sys.excepthook=short_err
x = {}
def f():
print(x['foo'])
f()
#...
error: tracebacks too long