Lib/traceback.py

   1 """Extract, format and print information about Python stack traces."""
   2
   3 import linecache
   4 import sys
   5 import types
   6
   7 __all__ = ['extract_stack', 'extract_tb', 'format_exception',
   8            'format_exception_only', 'format_list', 'format_stack',
   9            'format_tb', 'print_exc', 'format_exc', 'print_exception',
  10            'print_last', 'print_stack', 'print_tb', 'tb_lineno']
  11
  12 def _print(file, str='', terminator='\n'):
  13     file.write(str+terminator)
  14
  15
  16 def print_list(extracted_list, file=None):
  17     """Print the list of tuples as returned by extract_tb() or
  18     extract_stack() as a formatted stack trace to the given file."""
  19     if file is None:
  20         file = sys.stderr
  21     for filename, lineno, name, line in extracted_list:
  22         _print(file,
  23                '  File "%s", line %d, in %s' % (filename,lineno,name))
  24         if line:
  25             _print(file, '    %s' % line.strip())
  26
  27 def format_list(extracted_list):
  28     """Format a list of traceback entry tuples for printing.
  29
  30     Given a list of tuples as returned by extract_tb() or
  31     extract_stack(), return a list of strings ready for printing.
  32     Each string in the resulting list corresponds to the item with the
  33     same index in the argument list.  Each string ends in a newline;
  34     the strings may contain internal newlines as well, for those items
  35     whose source text line is not None.
  36     """
  37     list = []
  38     for filename, lineno, name, line in extracted_list:
  39         item = '  File "%s", line %d, in %s\n' % (filename,lineno,name)
  40         if line:
  41             item = item + '    %s\n' % line.strip()
  42         list.append(item)
  43     return list
  44
  45
  46 def print_tb(tb, limit=None, file=None):
  47     """Print up to 'limit' stack trace entries from the traceback 'tb'.
  48
  49     If 'limit' is omitted or None, all entries are printed.  If 'file'
  50     is omitted or None, the output goes to sys.stderr; otherwise
  51     'file' should be an open file or file-like object with a write()
  52     method.
  53     """
  54     if file is None:
  55         file = sys.stderr
  56     if limit is None:
  57         if hasattr(sys, 'tracebacklimit'):
  58             limit = sys.tracebacklimit
  59     n = 0
  60     while tb is not None and (limit is None or n < limit):
  61         f = tb.tb_frame
  62         lineno = tb.tb_lineno
  63         co = f.f_code
  64         filename = co.co_filename
  65         name = co.co_name
  66         _print(file,
  67                '  File "%s", line %d, in %s' % (filename,lineno,name))
  68         linecache.checkcache(filename)
  69         line = linecache.getline(filename, lineno, f.f_globals)
  70         if line: _print(file, '    ' + line.strip())
  71         tb = tb.tb_next
  72         n = n+1
  73
  74 def format_tb(tb, limit = None):
  75     """A shorthand for 'format_list(extract_stack(f, limit))."""
  76     return format_list(extract_tb(tb, limit))
  77
  78 def extract_tb(tb, limit = None):
  79     """Return list of up to limit pre-processed entries from traceback.
  80
  81     This is useful for alternate formatting of stack traces.  If
  82     'limit' is omitted or None, all entries are extracted.  A
  83     pre-processed stack trace entry is a quadruple (filename, line
  84     number, function name, text) representing the information that is
  85     usually printed for a stack trace.  The text is a string with
  86     leading and trailing whitespace stripped; if the source is not
  87     available it is None.
  88     """
  89     if limit is None:
  90         if hasattr(sys, 'tracebacklimit'):
  91             limit = sys.tracebacklimit
  92     list = []
  93     n = 0
  94     while tb is not None and (limit is None or n < limit):
  95         f = tb.tb_frame
  96         lineno = tb.tb_lineno
  97         co = f.f_code
  98         filename = co.co_filename
  99         name = co.co_name
 100         linecache.checkcache(filename)
 101         line = linecache.getline(filename, lineno, f.f_globals)
 102         if line: line = line.strip()
 103         else: line = None
 104         list.append((filename, lineno, name, line))
 105         tb = tb.tb_next
 106         n = n+1
 107     return list
 108
 109
 110 def print_exception(etype, value, tb, limit=None, file=None):
 111     """Print exception up to 'limit' stack trace entries from 'tb' to 'file'.
 112
 113     This differs from print_tb() in the following ways: (1) if
 114     traceback is not None, it prints a header "Traceback (most recent
 115     call last):"; (2) it prints the exception type and value after the
 116     stack trace; (3) if type is SyntaxError and value has the
 117     appropriate format, it prints the line where the syntax error
 118     occurred with a caret on the next line indicating the approximate
 119     position of the error.
 120     """
 121     if file is None:
 122         file = sys.stderr
 123     if tb:
 124         _print(file, 'Traceback (most recent call last):')
 125         print_tb(tb, limit, file)
 126     lines = format_exception_only(etype, value)
 127     for line in lines[:-1]:
 128         _print(file, line, ' ')
 129     _print(file, lines[-1], '')
 130
 131 def format_exception(etype, value, tb, limit = None):
 132     """Format a stack trace and the exception information.
 133
 134     The arguments have the same meaning as the corresponding arguments
 135     to print_exception().  The return value is a list of strings, each
 136     ending in a newline and some containing internal newlines.  When
 137     these lines are concatenated and printed, exactly the same text is
 138     printed as does print_exception().
 139     """
 140     if tb:
 141         list = ['Traceback (most recent call last):\n']
 142         list = list + format_tb(tb, limit)
 143     else:
 144         list = []
 145     list = list + format_exception_only(etype, value)
 146     return list
 147
 148 def format_exception_only(etype, value):
 149     """Format the exception part of a traceback.
 150
 151     The arguments are the exception type and value such as given by
 152     sys.last_type and sys.last_value. The return value is a list of
 153     strings, each ending in a newline.
 154
 155     Normally, the list contains a single string; however, for
 156     SyntaxError exceptions, it contains several lines that (when
 157     printed) display detailed information about where the syntax
 158     error occurred.
 159
 160     The message indicating which exception occurred is always the last
 161     string in the list.
 162
 163     """
 164
 165     # An instance should not have a meaningful value parameter, but
 166     # sometimes does, particularly for string exceptions, such as
 167     # >>> raise string1, string2  # deprecated
 168     #
 169     # Clear these out first because issubtype(string1, SyntaxError)
 170     # would throw another exception and mask the original problem.
 171     if (isinstance(etype, BaseException) or
 172         isinstance(etype, types.InstanceType) or
 173         type(etype) is str):
 174         return [_format_final_exc_line(etype, value)]
 175
 176     stype = etype.__name__
 177
 178     if not issubclass(etype, SyntaxError):
 179         return [_format_final_exc_line(stype, value)]
 180
 181     # It was a syntax error; show exactly where the problem was found.
 182     lines = []
 183     try:
 184         msg, (filename, lineno, offset, badline) = value
 185     except Exception:
 186         pass
 187     else:
 188         filename = filename or "<string>"
 189         lines.append('  File "%s", line %d\n' % (filename, lineno))
 190         if badline is not None:
 191             lines.append('    %s\n' % badline.strip())
 192             if offset is not None:
 193                 caretspace = badline[:offset].lstrip()
 194                 # non-space whitespace (likes tabs) must be kept for alignment
 195                 caretspace = ((c.isspace() and c or ' ') for c in caretspace)
 196                 # only three spaces to account for offset1 == pos 0
 197                 lines.append('   %s^\n' % ''.join(caretspace))
 198             value = msg
 199
 200     lines.append(_format_final_exc_line(stype, value))
 201     return lines
 202
 203 def _format_final_exc_line(etype, value):
 204     """Return a list of a single line -- normal case for format_exception_only"""
 205     if value is None or not str(value):
 206         line = "%s\n" % etype
 207     else:
 208         line = "%s: %s\n" % (etype, _some_str(value))
 209     return line
 210
 211 def _some_str(value):
 212     try:
 213         return str(value)
 214     except:
 215         return '<unprintable %s object>' % type(value).__name__
 216
 217
 218 def print_exc(limit=None, file=None):
 219     """Shorthand for 'print_exception(sys.exc_type, sys.exc_value, sys.exc_traceback, limit, file)'.
 220     (In fact, it uses sys.exc_info() to retrieve the same information
 221     in a thread-safe way.)"""
 222     if file is None:
 223         file = sys.stderr
 224     try:
 225         etype, value, tb = sys.exc_info()
 226         print_exception(etype, value, tb, limit, file)
 227     finally:
 228         etype = value = tb = None
 229
 230
 231 def format_exc(limit=None):
 232     """Like print_exc() but return a string."""
 233     try:
 234         etype, value, tb = sys.exc_info()
 235         return ''.join(format_exception(etype, value, tb, limit))
 236     finally:
 237         etype = value = tb = None
 238
 239
 240 def print_last(limit=None, file=None):
 241     """This is a shorthand for 'print_exception(sys.last_type,
 242     sys.last_value, sys.last_traceback, limit, file)'."""
 243     if file is None:
 244         file = sys.stderr
 245     print_exception(sys.last_type, sys.last_value, sys.last_traceback,
 246                     limit, file)
 247
 248
 249 def print_stack(f=None, limit=None, file=None):
 250     """Print a stack trace from its invocation point.
 251
 252     The optional 'f' argument can be used to specify an alternate
 253     stack frame at which to start. The optional 'limit' and 'file'
 254     arguments have the same meaning as for print_exception().
 255     """
 256     if f is None:
 257         try:
 258             raise ZeroDivisionError
 259         except ZeroDivisionError:
 260             f = sys.exc_info()[2].tb_frame.f_back
 261     print_list(extract_stack(f, limit), file)
 262
 263 def format_stack(f=None, limit=None):
 264     """Shorthand for 'format_list(extract_stack(f, limit))'."""
 265     if f is None:
 266         try:
 267             raise ZeroDivisionError
 268         except ZeroDivisionError:
 269             f = sys.exc_info()[2].tb_frame.f_back
 270     return format_list(extract_stack(f, limit))
 271
 272 def extract_stack(f=None, limit = None):
 273     """Extract the raw traceback from the current stack frame.
 274
 275     The return value has the same format as for extract_tb().  The
 276     optional 'f' and 'limit' arguments have the same meaning as for
 277     print_stack().  Each item in the list is a quadruple (filename,
 278     line number, function name, text), and the entries are in order
 279     from oldest to newest stack frame.
 280     """
 281     if f is None:
 282         try:
 283             raise ZeroDivisionError
 284         except ZeroDivisionError:
 285             f = sys.exc_info()[2].tb_frame.f_back
 286     if limit is None:
 287         if hasattr(sys, 'tracebacklimit'):
 288             limit = sys.tracebacklimit
 289     list = []
 290     n = 0
 291     while f is not None and (limit is None or n < limit):
 292         lineno = f.f_lineno
 293         co = f.f_code
 294         filename = co.co_filename
 295         name = co.co_name
 296         linecache.checkcache(filename)
 297         line = linecache.getline(filename, lineno, f.f_globals)
 298         if line: line = line.strip()
 299         else: line = None
 300         list.append((filename, lineno, name, line))
 301         f = f.f_back
 302         n = n+1
 303     list.reverse()
 304     return list
 305
 306 def tb_lineno(tb):
 307     """Calculate correct line number of traceback given in tb.
 308
 309     Obsolete in 2.3.
 310     """
 311     return tb.tb_lineno