Adds variables to python traceback. Simple, lightweight, controllable. Debug reasons of exceptions by logging or pretty printing colorful variable contexts for each frame in a stacktrace, showing e…

Very simple to use, but versatile when needed. Try for debug and keep for production.
It is useless work that darkens the heart.
Ursula K. Le Guin
Tired of useless job of putting all your variables into debug exception messages? Just stop it.
Automate it and clean your code. Once and for all.
Contents:Installation |
Quick Start
| Colors
| How does it save my time? |
Examples and recipes | Reference
| FAQ
Installation
pip install traceback-with-variables
conda install -c conda-forge traceback-with-variables
Quick Start
Using without code editing, running your script/command/module:
traceback-with-variables …script/tool/module with arguments…
Simplest usage in regular Python, for the whole program:
fromtraceback_with_variablesimportactivate_by_import
Simplest usage in Jupiter or IPython, for the whole program:
fromtraceback_with_variablesimportactivate_in_ipython_by_import
Decorator, for a single function:
@prints_tb# def main(): or def some_func(…):
Context, for a single code block:
Work with traceback lines in a custom manner:
return’\n’.join(iter_tb_lines(e))
Using a logger [with a decorator, with a context]:
withprinting_tb(file_=LoggerAsFile(logger)):
# or
@prints_tb(file_=LoggerAsFile(logger)):
Colors
How does it save my time?

• Turn a code totally covered by debug formatting from this:
  def main():
  sizes_str = sys.argv[1]
  h1, w1, h2, w2 = map(int, sizes_str.split())
  – try:
  return get_avg_ratio([h1, w1], [h2, w2])
  – except:- logger.error(f’something happened :(, variables = {locals()[:1000]}’)- raise- # or- raise MyToolException(f’something happened :(, variables = {locals()[:1000]}’)
  def get_avg_ratio(size1, size2):
  – try:
  return mean(get_ratio(h, w) for h, w in [size1, size2])
  – except:- logger.error(f’something happened :(, size1 = {size1}, size2 = {size2}’)- raise- # or- raise MyToolException(f’something happened :(, size1 = {size1}, size2 = {size2}’)
  def get_ratio(height, width):
  – try:
  return height / width
  – except:- logger.error(f’something happened :(, width = {width}, height = {height}’)- raise- # or- raise MyToolException(f’something happened :(, width = {width}, height = {height}’)
  into this (zero debug code):
  + from traceback_with_variables import activate_by_import
  def main():
  sizes_str = sys.argv[1]
  h1, w1, h2, w2 = map(int, sizes_str.split())
  return get_avg_ratio([h1, w1], [h2, w2])
  def get_avg_ratio(size1, size2):
  return mean(get_ratio(h, w) for h, w in [size1, size2])
  def get_ratio(height, width):
  return height / width
  And obtain total debug info spending 0 lines of code:
  Traceback with variables (most recent call last):
  File “./temp.py”, line 7, in main
  return get_avg_ratio([h1, w1], [h2, w2])
  sizes_str = ‘300 200 300 0’
  h1 = 300
  w1 = 200
  h2 = 300
  w2 = 0
  File “./temp.py”, line 10, in get_avg_ratio
  return mean([get_ratio(h, w) for h, w in [size1, size2]])
  size1 = [300, 200]
  size2 = [300, 0]
  File “./temp.py”, line 10, in <listcomp>
  return mean([get_ratio(h, w) for h, w in [size1, size2]])
  .0 = <tuple_iterator object at 0x7ff61e35b820>
  h = 300
  w = 0
  File “./temp.py”, line 13, in get_ratio
  return height / width
  height = 300
  width = 0
  builtins.ZeroDivisionError: division by zero
• Automate your logging too:
  logger=logging.getLogger(‘main’)
  defmain():
  …
  withprinting_tb(file_=LoggerAsFile(logger))
  …
  2020-03-30 18:24:31 main ERROR Traceback with variables (most recent call last):
  2020-03-30 18:24:31 main ERROR File “./temp.py”, line 7, in main
  2020-03-30 18:24:31 main ERROR return get_avg_ratio([h1, w1], [h2, w2])
  2020-03-30 18:24:31 main ERROR sizes_str = ‘300 200 300 0’
  2020-03-30 18:24:31 main ERROR h1 = 300
  2020-03-30 18:24:31 main ERROR w1 = 200
  2020-03-30 18:24:31 main ERROR h2 = 300
  2020-03-30 18:24:31 main ERROR w2 = 0
  2020-03-30 18:24:31 main ERROR File “./temp.py”, line 10, in get_avg_ratio
  2020-03-30 18:24:31 main ERROR return mean([get_ratio(h, w) for h, w in [size1, size2]])
  2020-03-30 18:24:31 main ERROR size1 = [300, 200]
  2020-03-30 18:24:31 main ERROR size2 = [300, 0]
  2020-03-30 18:24:31 main ERROR File “./temp.py”, line 10, in <listcomp>
  2020-03-30 18:24:31 main ERROR return mean([get_ratio(h, w) for h, w in [size1, size2]])
  2020-03-30 18:24:31 main ERROR .0 = <tuple_iterator object at 0x7ff412acb820>
  2020-03-30 18:24:31 main ERROR h = 300
  2020-03-30 18:24:31 main ERROR w = 0
  2020-03-30 18:24:31 main ERROR File “./temp.py”, line 13, in get_ratio
  2020-03-30 18:24:31 main ERROR return height / width
  2020-03-30 18:24:31 main ERROR height = 300
  2020-03-30 18:24:31 main ERROR width = 0
  2020-03-30 18:24:31 main ERROR builtins.ZeroDivisionError: division by zero
• Free your exceptions of unnecessary information load:
  defmake_a_cake(sugar, eggs, milk, flour, salt, water):
  is_sweet=sugar>saltis_vegan=not (eggsormilk)
  is_huge= (sugar+eggs+milk+flour+salt+water>10000)
  ifnot (is_sweetoris_veganoris_huge):
  raiseValueError(‘This is unacceptable, guess why!’)
  …
• Should I use it after debugging is over, i.e. in production?
  Yes, of course! That way it might save you even more time.

• Stop this tedious practice in production:
  step 1: Notice some exception in a production service. step 2: Add more printouts, logging, and exception messages. step 3: Rerun the service. step 4: Wait till (hopefully) the bug repeats. step 5: Examine the printouts and possibly add some more info (then go back to step 2). step 6: Erase all recently added printouts, logging and exception messages. step 7: Go back to step 1 once bugs appear.

Examples and recipes
Reference
All functions have output customization

• max_value_str_len max length of each variable string, -1 to disable, default=1000
• max_exc_str_len max length of exception, should variable print fail, -1 to disable, default=10000
• num_context_lines number of lines around the target code line to print, default=1
• ellipsis_ string to denote long strings truncation, default=…
• file_ where to print exception, a file or a wrapped logger, default=sys.stderr i.e. usual printing to console
• color_scheme one of ColorSchemes: .auto, .none , .common, .nice, .synthwave

Just import it. No arguments, for real quick use in regular Python.
fromtraceback_with_variablesimportactivate_by_import
Just import it. No arguments, for real quick use in Jupyter or IPython.
fromtraceback_with_variablesimportactivate_in_ipython_by_import
Call once in the beginning of your program, to change how traceback after an uncaught exception looks.
defmain():
override_print_tb(…)
Function decorator, used for logging or simple printing of scoped tracebacks with variables. I.e. traceback is shorter as it includes only frames inside the function call. Program exiting due to unhandled exception still prints a usual traceback.
@prints_tbdeff(…):
@prints_tb(…)deff(…):
Context manager (i.e. with …), used for logging or simple printing of scoped tracebacks with variables. I.e. traceback is shorter as it includes only frames inside the with scope. Program exiting due to unhandled exception still prints a usual traceback.
A logger-to-file wrapper, to pass a logger to print tools as a file.
Iterates the lines, which are usually printed one-by-one in terminal.
FAQ

• In Windows console crash messages have no colors.
  The default Windows console/terminal cannot print [so called ansi] colors, but this is
  fixable
  , especially with modern Windows versions. Therefore colors are disabled by default,
  but you can enable them and check if it works in your case.
  You can force enable colors by passing –color-scheme common (for complete list of colors pass –help) console argument.
• Windows console prints junk symbols when colors are enabled.
  The default Windows console/terminal cannot print [so called ansi] colors, but this is
  fixable
  , especially with modern Windows versions. If for some reason the colors are wrongly enabled by default,
  you can force disable colors by passing –color-scheme none console argument.
• Bash tools like grep sometimes fail to digest the output when used with pipes (|) because of colors.
  Please disable colors by passing –color-scheme none console argument.
  The choice for keeping colors in piped output was made to allow convenient usage of head, tail, file redirection etc.
  In cases like | grep it might have issues, in which case you can disable colors.
• Output redirected to a file in > output.txt manner has no colors when I cat it.
  This is considered a rare use case, so colors are disabled by default when outputting to a file.
  But you can force enable colors by passing –color-scheme common (for complete list of colors pass –help) console argument.
• activate_by_import or override_print_tb don’t work in Jupiter or IPython as if not called at all.
  Don’t forget to use ipython=True or import activate_in_ipython_by_import since Jupyer/Ipython handles exceptions differently than regular Python.
• My code doesn’t work.
  Please post your case. You are very welcome!
• Other questions or requests to elaborate answers.
  Please post your question or request. You are very welcome!