314 lines
11 KiB
Python
314 lines
11 KiB
Python
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"""Extract, format and print information about Python stack traces."""
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import linecache
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import sys
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import operator
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__all__ = ['extract_stack', 'extract_tb', 'format_exception',
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'format_exception_only', 'format_list', 'format_stack',
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'format_tb', 'print_exc', 'format_exc', 'print_exception',
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'print_last', 'print_stack', 'print_tb',
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'clear_frames']
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#
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# Formatting and printing lists of traceback lines.
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#
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def _format_list_iter(extracted_list):
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for filename, lineno, name, line in extracted_list:
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item = ' File "{}", line {}, in {}\n'.format(filename, lineno, name)
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if line:
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item = item + ' {}\n'.format(line.strip())
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yield item
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def print_list(extracted_list, file=None):
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"""Print the list of tuples as returned by extract_tb() or
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extract_stack() as a formatted stack trace to the given file."""
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if file is None:
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file = sys.stderr
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for item in _format_list_iter(extracted_list):
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print(item, file=file, end="")
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def format_list(extracted_list):
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"""Format a list of traceback entry tuples for printing.
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Given a list of tuples as returned by extract_tb() or
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extract_stack(), return a list of strings ready for printing.
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Each string in the resulting list corresponds to the item with the
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same index in the argument list. Each string ends in a newline;
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the strings may contain internal newlines as well, for those items
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whose source text line is not None.
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"""
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return list(_format_list_iter(extracted_list))
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#
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# Printing and Extracting Tracebacks.
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#
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# extractor takes curr and needs to return a tuple of:
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# - Frame object
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# - Line number
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# - Next item (same type as curr)
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# In practice, curr is either a traceback or a frame.
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def _extract_tb_or_stack_iter(curr, limit, extractor):
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if limit is None:
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limit = getattr(sys, 'tracebacklimit', None)
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n = 0
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while curr is not None and (limit is None or n < limit):
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f, lineno, next_item = extractor(curr)
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co = f.f_code
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filename = co.co_filename
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name = co.co_name
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linecache.checkcache(filename)
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line = linecache.getline(filename, lineno, f.f_globals)
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if line:
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line = line.strip()
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else:
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line = None
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yield (filename, lineno, name, line)
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curr = next_item
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n += 1
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def _extract_tb_iter(tb, limit):
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return _extract_tb_or_stack_iter(
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tb, limit,
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operator.attrgetter("tb_frame", "tb_lineno", "tb_next"))
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def print_tb(tb, limit=None, file=None):
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"""Print up to 'limit' stack trace entries from the traceback 'tb'.
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If 'limit' is omitted or None, all entries are printed. If 'file'
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is omitted or None, the output goes to sys.stderr; otherwise
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'file' should be an open file or file-like object with a write()
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method.
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"""
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print_list(extract_tb(tb, limit=limit), file=file)
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def format_tb(tb, limit=None):
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"""A shorthand for 'format_list(extract_tb(tb, limit))'."""
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return format_list(extract_tb(tb, limit=limit))
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def extract_tb(tb, limit=None):
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"""Return list of up to limit pre-processed entries from traceback.
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This is useful for alternate formatting of stack traces. If
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'limit' is omitted or None, all entries are extracted. A
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pre-processed stack trace entry is a quadruple (filename, line
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number, function name, text) representing the information that is
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usually printed for a stack trace. The text is a string with
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leading and trailing whitespace stripped; if the source is not
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available it is None.
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"""
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return list(_extract_tb_iter(tb, limit=limit))
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#
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# Exception formatting and output.
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#
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_cause_message = (
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"\nThe above exception was the direct cause "
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"of the following exception:\n")
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_context_message = (
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"\nDuring handling of the above exception, "
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"another exception occurred:\n")
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def _iter_chain(exc, custom_tb=None, seen=None):
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if seen is None:
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seen = set()
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seen.add(exc)
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its = []
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context = exc.__context__
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cause = exc.__cause__
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if cause is not None and cause not in seen:
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its.append(_iter_chain(cause, False, seen))
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its.append([(_cause_message, None)])
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elif (context is not None and
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not exc.__suppress_context__ and
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context not in seen):
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its.append(_iter_chain(context, None, seen))
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its.append([(_context_message, None)])
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its.append([(exc, custom_tb or exc.__traceback__)])
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# itertools.chain is in an extension module and may be unavailable
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for it in its:
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yield from it
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def _format_exception_iter(etype, value, tb, limit, chain):
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if chain:
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values = _iter_chain(value, tb)
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else:
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values = [(value, tb)]
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for value, tb in values:
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if isinstance(value, str):
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# This is a cause/context message line
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yield value + '\n'
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continue
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if tb:
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yield 'Traceback (most recent call last):\n'
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yield from _format_list_iter(_extract_tb_iter(tb, limit=limit))
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yield from _format_exception_only_iter(type(value), value)
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def print_exception(etype, value, tb, limit=None, file=None, chain=True):
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"""Print exception up to 'limit' stack trace entries from 'tb' to 'file'.
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This differs from print_tb() in the following ways: (1) if
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traceback is not None, it prints a header "Traceback (most recent
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call last):"; (2) it prints the exception type and value after the
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stack trace; (3) if type is SyntaxError and value has the
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appropriate format, it prints the line where the syntax error
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occurred with a caret on the next line indicating the approximate
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position of the error.
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"""
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if file is None:
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file = sys.stderr
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for line in _format_exception_iter(etype, value, tb, limit, chain):
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print(line, file=file, end="")
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def format_exception(etype, value, tb, limit=None, chain=True):
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"""Format a stack trace and the exception information.
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The arguments have the same meaning as the corresponding arguments
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to print_exception(). The return value is a list of strings, each
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ending in a newline and some containing internal newlines. When
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these lines are concatenated and printed, exactly the same text is
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printed as does print_exception().
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"""
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return list(_format_exception_iter(etype, value, tb, limit, chain))
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def format_exception_only(etype, value):
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"""Format the exception part of a traceback.
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The arguments are the exception type and value such as given by
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sys.last_type and sys.last_value. The return value is a list of
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strings, each ending in a newline.
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Normally, the list contains a single string; however, for
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SyntaxError exceptions, it contains several lines that (when
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printed) display detailed information about where the syntax
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error occurred.
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The message indicating which exception occurred is always the last
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string in the list.
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"""
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return list(_format_exception_only_iter(etype, value))
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def _format_exception_only_iter(etype, value):
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# Gracefully handle (the way Python 2.4 and earlier did) the case of
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# being called with (None, None).
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if etype is None:
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yield _format_final_exc_line(etype, value)
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return
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stype = etype.__name__
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smod = etype.__module__
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if smod not in ("__main__", "builtins"):
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stype = smod + '.' + stype
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if not issubclass(etype, SyntaxError):
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yield _format_final_exc_line(stype, value)
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return
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# It was a syntax error; show exactly where the problem was found.
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filename = value.filename or "<string>"
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lineno = str(value.lineno) or '?'
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yield ' File "{}", line {}\n'.format(filename, lineno)
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badline = value.text
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offset = value.offset
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if badline is not None:
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yield ' {}\n'.format(badline.strip())
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if offset is not None:
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caretspace = badline.rstrip('\n')
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offset = min(len(caretspace), offset) - 1
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caretspace = caretspace[:offset].lstrip()
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# non-space whitespace (likes tabs) must be kept for alignment
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caretspace = ((c.isspace() and c or ' ') for c in caretspace)
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yield ' {}^\n'.format(''.join(caretspace))
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msg = value.msg or "<no detail available>"
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yield "{}: {}\n".format(stype, msg)
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def _format_final_exc_line(etype, value):
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valuestr = _some_str(value)
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if value is None or not valuestr:
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line = "%s\n" % etype
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else:
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line = "%s: %s\n" % (etype, valuestr)
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return line
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def _some_str(value):
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try:
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return str(value)
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except:
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return '<unprintable %s object>' % type(value).__name__
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def print_exc(limit=None, file=None, chain=True):
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"""Shorthand for 'print_exception(*sys.exc_info(), limit, file)'."""
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print_exception(*sys.exc_info(), limit=limit, file=file, chain=chain)
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def format_exc(limit=None, chain=True):
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"""Like print_exc() but return a string."""
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return "".join(format_exception(*sys.exc_info(), limit=limit, chain=chain))
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def print_last(limit=None, file=None, chain=True):
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"""This is a shorthand for 'print_exception(sys.last_type,
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sys.last_value, sys.last_traceback, limit, file)'."""
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if not hasattr(sys, "last_type"):
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raise ValueError("no last exception")
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print_exception(sys.last_type, sys.last_value, sys.last_traceback,
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limit, file, chain)
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#
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# Printing and Extracting Stacks.
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#
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def _extract_stack_iter(f, limit=None):
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return _extract_tb_or_stack_iter(
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f, limit, lambda f: (f, f.f_lineno, f.f_back))
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def _get_stack(f):
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if f is None:
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f = sys._getframe().f_back.f_back
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return f
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def print_stack(f=None, limit=None, file=None):
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"""Print a stack trace from its invocation point.
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The optional 'f' argument can be used to specify an alternate
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stack frame at which to start. The optional 'limit' and 'file'
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arguments have the same meaning as for print_exception().
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"""
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print_list(extract_stack(_get_stack(f), limit=limit), file=file)
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def format_stack(f=None, limit=None):
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"""Shorthand for 'format_list(extract_stack(f, limit))'."""
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return format_list(extract_stack(_get_stack(f), limit=limit))
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def extract_stack(f=None, limit=None):
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"""Extract the raw traceback from the current stack frame.
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The return value has the same format as for extract_tb(). The
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optional 'f' and 'limit' arguments have the same meaning as for
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print_stack(). Each item in the list is a quadruple (filename,
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line number, function name, text), and the entries are in order
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from oldest to newest stack frame.
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"""
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stack = list(_extract_stack_iter(_get_stack(f), limit=limit))
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stack.reverse()
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return stack
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def clear_frames(tb):
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"Clear all references to local variables in the frames of a traceback."
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while tb is not None:
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try:
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tb.tb_frame.clear()
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except RuntimeError:
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# Ignore the exception raised if the frame is still executing.
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pass
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tb = tb.tb_next
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