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         etype is None or 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.args
 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     valuestr = _some_str(value)
 206     if value is None or not valuestr:
 207         line = "%s\n" % etype
 208     else:
 209         line = "%s: %s\n" % (etype, valuestr)
 210     return line
 211
 212 def _some_str(value):
 213     try:
 214         return str(value)
 215     except:
 216         return '<unprintable %s object>' % type(value).__name__
 217
 218
 219 def print_exc(limit=None, file=None):
 220     """Shorthand for 'print_exception(sys.exc_type, sys.exc_value, sys.exc_traceback, limit, file)'.
 221     (In fact, it uses sys.exc_info() to retrieve the same information
 222     in a thread-safe way.)"""
 223     if file is None:
 224         file = sys.stderr
 225     try:
 226         etype, value, tb = sys.exc_info()
 227         print_exception(etype, value, tb, limit, file)
 228     finally:
 229         etype = value = tb = None
 230
 231
 232 def format_exc(limit=None):
 233     """Like print_exc() but return a string."""
 234     try:
 235         etype, value, tb = sys.exc_info()
 236         return ''.join(format_exception(etype, value, tb, limit))
 237     finally:
 238         etype = value = tb = None
 239
 240
 241 def print_last(limit=None, file=None):
 242     """This is a shorthand for 'print_exception(sys.last_type,
 243     sys.last_value, sys.last_traceback, limit, file)'."""
 244     if not hasattr(sys, "last_type"):
 245         raise ValueError("no last exception")
 246     if file is None:
 247         file = sys.stderr
 248     print_exception(sys.last_type, sys.last_value, sys.last_traceback,
 249                     limit, file)
 250
 251
 252 def print_stack(f=None, limit=None, file=None):
 253     """Print a stack trace from its invocation point.
 254
 255     The optional 'f' argument can be used to specify an alternate
 256     stack frame at which to start. The optional 'limit' and 'file'
 257     arguments have the same meaning as for print_exception().
 258     """
 259     if f is None:
 260         try:
 261             raise ZeroDivisionError
 262         except ZeroDivisionError:
 263             f = sys.exc_info()[2].tb_frame.f_back
 264     print_list(extract_stack(f, limit), file)
 265
 266 def format_stack(f=None, limit=None):
 267     """Shorthand for 'format_list(extract_stack(f, limit))'."""
 268     if f is None:
 269         try:
 270             raise ZeroDivisionError
 271         except ZeroDivisionError:
 272             f = sys.exc_info()[2].tb_frame.f_back
 273     return format_list(extract_stack(f, limit))
 274
 275 def extract_stack(f=None, limit = None):
 276     """Extract the raw traceback from the current stack frame.
 277
 278     The return value has the same format as for extract_tb().  The
 279     optional 'f' and 'limit' arguments have the same meaning as for
 280     print_stack().  Each item in the list is a quadruple (filename,
 281     line number, function name, text), and the entries are in order
 282     from oldest to newest stack frame.
 283     """
 284     if f is None:
 285         try:
 286             raise ZeroDivisionError
 287         except ZeroDivisionError:
 288             f = sys.exc_info()[2].tb_frame.f_back
 289     if limit is None:
 290         if hasattr(sys, 'tracebacklimit'):
 291             limit = sys.tracebacklimit
 292     list = []
 293     n = 0
 294     while f is not None and (limit is None or n < limit):
 295         lineno = f.f_lineno
 296         co = f.f_code
 297         filename = co.co_filename
 298         name = co.co_name
 299         linecache.checkcache(filename)
 300         line = linecache.getline(filename, lineno, f.f_globals)
 301         if line: line = line.strip()
 302         else: line = None
 303         list.append((filename, lineno, name, line))
 304         f = f.f_back
 305         n = n+1
 306     list.reverse()
 307     return list
 308
 309 def tb_lineno(tb):
 310     """Calculate correct line number of traceback given in tb.
 311
 312     Obsolete in 2.3.
 313     """
 314     return tb.tb_lineno