Print more detailed call stacks, with current variable values etc
Project description
Python stack formatter
This prints detailed Python stack traces, with more source context and current variable values. It's a quick way to see what your code is doing when your only debugging tool is a log file 😱
Before
After
Installation
pip install stackprinter
Logging exception tracebacks
Call show
or format
inside an except block to trace the current exception. show
prints to stderr, format
returns a string. You can also pass exception objects explicitly.
By default, this will generate plain text. Pass style='color'
to get funky terminal colors. For all the config options, see the docs of format()
.
import stackprinter
try:
something()
except:
stackprinter.show() # grab the current exception and print a traceback to stderr
# ...or only return a string, e.g. for logging.
message = stackprinter.format()
logging.log(message)
There's also stackprinter.set_excepthook
which replaces the default python crash message (so it works automatically without manual try/except... unless you're in IPython).
Printing the call stack of another thread
Pass a thread object to show
or format
.
thread = threading.Thread(target=something)
thread.start()
while True:
stackprinter.show(thread) # or format(thread)
time.sleep(0.1)
Printing the call stack of the current thread
Call show
or format
outside of exception handling.
stackprinter.show() # or format()
For people who don't like context dependent methods, there's also show/format_current_stack()
, which does the same even inside except blocks.
Tracing a piece of code as it is executed
More for curiosity than anything else, you can watch a piece of code execute step-by-step, printing a trace of all calls & returns 'live' as they are happening. Slows everything down though, of course.
tp = stackprinter.TracePrinter(style='color', suppressed_paths=[r"lib/python.*/site-packages/numpy"])
tp.enable()
a = np.ones(111)
dosomething(a)
tp.disable()
How it works
Basically, this is a frame formatter. For each frame on the call stack, it grabs the source code to find out which source lines reference which variables. Then it displays code and variables in the neighbourhood of the last executed line.
Since this already requires a map of where each variable occurs in the code, it was hard not to also implement the whole semantic highlighting color thing seen in the screenshots. The colors are ANSI escape codes now, but it should be fairly straightforward™ to render the underlying data without any 1980ies terminal technology. Say, a foldable and clickable HTML page with downloadable pickled variables. But for now you'll have to pipe the ANSI strings through ansi2html or something.
Caveats
This displays variable values as they are at the time of formatting. In multi-threaded programs, variables can change while we're busy walking the stack & printing them. So, if nothing seems to make sense, consider that your exception and the traceback messages are from slightly different times. Sadly, there is no responsible way to freeze all other threads as soon as we want to inspect some thread's call stack (...or is there?)
Docs
*coughs*
For now, just look at all the doc strings, e.g. of format()
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