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better_exchook

A nicer drop-in-replacement for Python sys.excepthook, i.e. it prints stack traces with extended information. It will add some useful information for each frame, like printing the relevant variables (relevant = referenced in the code line). Also see Python source and comments for further details.

Features

  • Shows locals/globals per frame, but only those used in the current statement. It does this by a simple Python code parser.
  • Multi-line Python statements in the stack trace output, in case the statement goes over multiple lines.
  • Shows full function qualified name (not just co_name).
  • Colored/formatted output of each frame.
  • Syntax highlighting for the Python source code.
  • Support for DomTerm, where it folds all the details of each stack frame away by default, and thus provides a much more comprehensive overview, while still providing all the details when needed.

Installation

You can just copy over the single file better_exchook.py to your project.

Or alternatively, it is also available on PyPI and can be installed via:

pip install better_exchook

Usage

import better_exchook
better_exchook.install()  # will just do: sys.excepthook = better_exchook

Examples

Python example code:

try:
    x = {1:2, "a":"b"}
    def f():
        y = "foo"
        x, 42, sys.stdin.__class__, sys.exc_info, y, z
    f()
except Exception:
    better_exchook.better_exchook(*sys.exc_info())

Output:

EXCEPTION
Traceback (most recent call last):
  File "better_exchook.py", line 478, in <module>
    line: f()
    locals:
      f = <local> <function f at 0x107f1de60>
  File "better_exchook.py", line 477, in f
    line: x, 42, sys.stdin.__class__, sys.exc_info, y, z
    locals:
      x = <global> {'a': 'b', 1: 2}
      sys = <global> <module 'sys' (built-in)>
      sys.stdin = <global> <open file '<stdin>', mode 'r' at 0x107d9f0c0>
      sys.stdin.__class__ = <global> <type 'file'>
      sys.exc_info = <global> <built-in function exc_info>
      y = <local> 'foo'
      z = <not found>
NameError: global name 'z' is not defined

Python example code:

try:
    f = lambda x: None
    f(x, y)
except Exception:
    better_exchook.better_exchook(*sys.exc_info())

Output:

EXCEPTION
Traceback (most recent call last):
  File "better_exchook.py", line 484, in <module>
    line: f(x, y)
    locals:
      f = <local> <function <lambda> at 0x107f1df50>
      x = <local> {'a': 'b', 1: 2}
      y = <not found>
NameError: name 'y' is not defined

Python example code:

try:
    (lambda x: None)(__name__,
                     42)  # multiline
except Exception:
    better_exchook.better_exchook(*sys.exc_info())

Output:

EXCEPTION
Traceback (most recent call last):
  File "better_exchook.py", line 490, in <module>
    line: (lambda x: None)(__name__,
                           42)  # multiline
    locals:
      x = <local> {'a': 'b', 1: 2}
      __name__ = <local> '__main__', len = 8
TypeError: <lambda>() takes exactly 1 argument (2 given)

Python example code:

# use this to overwrite the global exception handler
sys.excepthook = better_exchook.better_exchook
# and fail
finalfail(sys)

Output:

EXCEPTION
Traceback (most recent call last):
  File "better_exchook.py", line 497, in <module>
    line: finalfail(sys)
    locals:
      finalfail = <not found>
      sys = <local> <module 'sys' (built-in)>
NameError: name 'finalfail' is not defined

Screenshot:

https://gist.githubusercontent.com/albertz/a4ce78e5ccd037041638777f10b10327/raw/7ec2bb7079dbd56119d498f20905404cb2d812c0/screenshot1.png

Screencast with DomTerm:

https://gist.githubusercontent.com/albertz/a4ce78e5ccd037041638777f10b10327/raw/7ec2bb7079dbd56119d498f20905404cb2d812c0/screencast-domterm.gif

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-- Albert Zeyer, <http://www.az2000.de>

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nice Python exception hook replacement

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