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:
 128         _print(file, line, '')
 129
 130 def format_exception(etype, value, tb, limit = None):
 131     """Format a stack trace and the exception information.
 132
 133     The arguments have the same meaning as the corresponding arguments
 134     to print_exception().  The return value is a list of strings, each
 135     ending in a newline and some containing internal newlines.  When
 136     these lines are concatenated and printed, exactly the same text is
 137     printed as does print_exception().
 138     """
 139     if tb:
 140         list = ['Traceback (most recent call last):\n']
 141         list = list + format_tb(tb, limit)
 142     else:
 143         list = []
 144     list = list + format_exception_only(etype, value)
 145     return list
 146
 147 def format_exception_only(etype, value):
 148     """Format the exception part of a traceback.
 149
 150     The arguments are the exception type and value such as given by
 151     sys.last_type and sys.last_value. The return value is a list of
 152     strings, each ending in a newline.
 153
 154     Normally, the list contains a single string; however, for
 155     SyntaxError exceptions, it contains several lines that (when
 156     printed) display detailed information about where the syntax
 157     error occurred.
 158
 159     The message indicating which exception occurred is always the last
 160     string in the list.
 161
 162     """
 163
 164     # An instance should not have a meaningful value parameter, but
 165     # sometimes does, particularly for string exceptions, such as
 166     # >>> raise string1, string2  # deprecated
 167     #
 168     # Clear these out first because issubtype(string1, SyntaxError)
 169     # would throw another exception and mask the original problem.
 170     if (isinstance(etype, BaseException) or
 171         isinstance(etype, types.InstanceType) or
 172         etype is None or type(etype) is str):
 173         return [_format_final_exc_line(etype, value)]
 174
 175     stype = etype.__name__
 176
 177     if not issubclass(etype, SyntaxError):
 178         return [_format_final_exc_line(stype, value)]
 179
 180     # It was a syntax error; show exactly where the problem was found.
 181     lines = []
 182     try:
 183         msg, (filename, lineno, offset, badline) = value.args
 184     except Exception:
 185         pass
 186     else:
 187         filename = filename or "<string>"
 188         lines.append('  File "%s", line %d\n' % (filename, lineno))
 189         if badline is not None:
 190             lines.append('    %s\n' % badline.strip())
 191             if offset is not None:
 192                 caretspace = badline.rstrip('\n')[:offset].lstrip()
 193                 # non-space whitespace (likes tabs) must be kept for alignment
 194                 caretspace = ((c.isspace() and c or ' ') for c in caretspace)
 195                 # only three spaces to account for offset1 == pos 0
 196                 lines.append('   %s^\n' % ''.join(caretspace))
 197         value = msg
 198
 199     lines.append(_format_final_exc_line(stype, value))
 200     return lines
 201
 202 def _format_final_exc_line(etype, value):
 203     """Return a list of a single line -- normal case for format_exception_only"""
 204     valuestr = _some_str(value)
 205     if value is None or not valuestr:
 206         line = "%s\n" % etype
 207     else:
 208         line = "%s: %s\n" % (etype, valuestr)
 209     return line
 210
 211 def _some_str(value):
 212     try:
 213         return str(value)
 214     except Exception:
 215         pass
 216     try:
 217         value = unicode(value)
 218         return value.encode("ascii", "backslashreplace")
 219     except Exception:
 220         pass
 221     return '<unprintable %s object>' % type(value).__name__
 222
 223
 224 def print_exc(limit=None, file=None):
 225     """Shorthand for 'print_exception(sys.exc_type, sys.exc_value, sys.exc_traceback, limit, file)'.
 226     (In fact, it uses sys.exc_info() to retrieve the same information
 227     in a thread-safe way.)"""
 228     if file is None:
 229         file = sys.stderr
 230     try:
 231         etype, value, tb = sys.exc_info()
 232         print_exception(etype, value, tb, limit, file)
 233     finally:
 234         etype = value = tb = None
 235
 236
 237 def format_exc(limit=None):
 238     """Like print_exc() but return a string."""
 239     try:
 240         etype, value, tb = sys.exc_info()
 241         return ''.join(format_exception(etype, value, tb, limit))
 242     finally:
 243         etype = value = tb = None
 244
 245
 246 def print_last(limit=None, file=None):
 247     """This is a shorthand for 'print_exception(sys.last_type,
 248     sys.last_value, sys.last_traceback, limit, file)'."""
 249     if not hasattr(sys, "last_type"):
 250         raise ValueError("no last exception")
 251     if file is None:
 252         file = sys.stderr
 253     print_exception(sys.last_type, sys.last_value, sys.last_traceback,
 254                     limit, file)
 255
 256
 257 def print_stack(f=None, limit=None, file=None):
 258     """Print a stack trace from its invocation point.
 259
 260     The optional 'f' argument can be used to specify an alternate
 261     stack frame at which to start. The optional 'limit' and 'file'
 262     arguments have the same meaning as for print_exception().
 263     """
 264     if f is None:
 265         try:
 266             raise ZeroDivisionError
 267         except ZeroDivisionError:
 268             f = sys.exc_info()[2].tb_frame.f_back
 269     print_list(extract_stack(f, limit), file)
 270
 271 def format_stack(f=None, limit=None):
 272     """Shorthand for 'format_list(extract_stack(f, limit))'."""
 273     if f is None:
 274         try:
 275             raise ZeroDivisionError
 276         except ZeroDivisionError:
 277             f = sys.exc_info()[2].tb_frame.f_back
 278     return format_list(extract_stack(f, limit))
 279
 280 def extract_stack(f=None, limit = None):
 281     """Extract the raw traceback from the current stack frame.
 282
 283     The return value has the same format as for extract_tb().  The
 284     optional 'f' and 'limit' arguments have the same meaning as for
 285     print_stack().  Each item in the list is a quadruple (filename,
 286     line number, function name, text), and the entries are in order
 287     from oldest to newest stack frame.
 288     """
 289     if f is None:
 290         try:
 291             raise ZeroDivisionError
 292         except ZeroDivisionError:
 293             f = sys.exc_info()[2].tb_frame.f_back
 294     if limit is None:
 295         if hasattr(sys, 'tracebacklimit'):
 296             limit = sys.tracebacklimit
 297     list = []
 298     n = 0
 299     while f is not None and (limit is None or n < limit):
 300         lineno = f.f_lineno
 301         co = f.f_code
 302         filename = co.co_filename
 303         name = co.co_name
 304         linecache.checkcache(filename)
 305         line = linecache.getline(filename, lineno, f.f_globals)
 306         if line: line = line.strip()
 307         else: line = None
 308         list.append((filename, lineno, name, line))
 309         f = f.f_back
 310         n = n+1
 311     list.reverse()
 312     return list
 313
 314 def tb_lineno(tb):
 315     """Calculate correct line number of traceback given in tb.
 316
 317     Obsolete in 2.3.
 318     """
 319     return tb.tb_lineno