Lib/traceback.py

cpython 3.14 @ ab2d84fe1023/Lib/traceback.py ↗

Lib/traceback.py provides the Python API for formatting and printing tracebacks. The low-level C traceback printer (Python/traceback.c) handles sys.stderr output during exception propagation; this module provides programmatic access to the same information.

Map

Lines	Symbol	Role
1-100	print_tb, print_exception, format_tb, format_exception	Function-level API
101-300	StackSummary, FrameSummary	Stack capture and formatting
301-600	TracebackException	Rich exception object with format() method
601-820	extract_tb, extract_stack	Legacy extraction functions

Reading

TracebackException

TracebackException.from_exception(exc) captures the exception's type, value, and traceback, plus __cause__ and __context__ chains, into a structured object. format() yields formatted lines suitable for sys.stderr.write.

# CPython: Lib/traceback.py:320 TracebackException.from_exception
@classmethod
def from_exception(cls, exc, *, limit=None, lookup_lines=True, capture_locals=False):
    ...
    te = cls(type(exc), exc, exc.__traceback__, limit=limit, ...)
    return te

FrameSummary

FrameSummary captures the filename, line number, function name, and optionally the source line text. Line text is fetched lazily from linecache.getline.

format_exception_only

format_exception_only(exc) formats the exception type and value without the traceback. For SyntaxError, it also formats the filename, line number, and caret marker.

StackSummary.extract

StackSummary.extract(frame_gen, limit=None, lookup_lines=True) iterates a sequence of (frame, lineno) pairs (typically from walk_stack or walk_tb) and returns a StackSummary list of FrameSummary objects.

gopy notes

Not yet ported. traceback depends on linecache for source line fetching. The TracebackException class is pure Python. Planned path: module/traceback/.