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From: Oscar Benjamin <oscar.j.benjamin@gmail.com>
Date: Sat, 16 Mar 2013 21:19:34 +0000
Subject: Re: PyWart: NameError trackbacks are superfluous
To: Rick Johnson <rantingrickjohnson@gmail.com>
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Xref: csiph.com comp.lang.python:41329

On 16 March 2013 18:27, Rick Johnson <rantingrickjohnson@gmail.com> wrote:
>
> Sometimes many levels of trace messages can be helpful when detecting bug=
s, however, in the case of NameErrors,  these "nuggets" ejected from deep w=
ithin the bowls of the Python interpreter are nothing more than steaming pi=
les of incomprehensible crap!
>
> We don't need multiple layers of traces for NameErrors. Python does not h=
ave *real* global variables; and thank Guido for that! All we need to know =
is which module the error occurred in AND which line of that module contain=
s the offensive lookup of a name that does not exist.
[SNIP]

NameErrors can occur conditionally depending on e.g. the arguments to
a function. Consider the following script:

  # tmp.py
  def broken(x):
      if x > 2:
          print(x)
      else:
          print(undefined_name)

  broken(1)

When run it gives a NameError with a traceback:

$ python tmp.py
Traceback (most recent call last):
  File "tmp3.py", line 8, in <module>
    broken(1)
  File "tmp3.py", line 6, in broken
    print(undefined_name)
NameError: global name 'undefined_name' is not defined

The traceback shows the arguments passed to the broken function that
caused the NameError to be generated. Different arguments would not
have generated the NameError. This information can be useful if the
logic of the function in question is complicated. It also hints at why
you were calling the function and what your code is trying to do.


Oscar