cgitb.py - This code provides a way to display Python excep…

/Lib/cgitb.py

http://unladen-swallow.googlecode.com/ · Python · 318 lines · 279 code · 18 blank · 21 comment · 27 complexity · 5649cc63c8b3919b72a18bdbc4c47036 MD5 · raw file

"""More comprehensive traceback formatting for Python scripts.

To enable this module, do:

    import cgitb; cgitb.enable()

at the top of your script.  The optional arguments to enable() are:

    display     - if true, tracebacks are displayed in the web browser
    logdir      - if set, tracebacks are written to files in this directory
    context     - number of lines of source code to show for each stack frame
    format      - 'text' or 'html' controls the output format

By default, tracebacks are displayed but not saved, the context is 5 lines
and the output format is 'html' (for backwards compatibility with the
original use of this module)

Alternatively, if you have caught an exception and want cgitb to display it
for you, call cgitb.handler().  The optional argument to handler() is a
3-item tuple (etype, evalue, etb) just like the value of sys.exc_info().
The default handler displays output as HTML.
"""

__author__ = 'Ka-Ping Yee'

__version__ = '$Revision: 55348 $'

import sys

def reset():
    """Return a string that resets the CGI and browser to a known state."""
    return '''<!--: spam
Content-Type: text/html

<body bgcolor="#f0f0f8"><font color="#f0f0f8" size="-5"> -->
<body bgcolor="#f0f0f8"><font color="#f0f0f8" size="-5"> --> -->
</font> </font> </font> </script> </object> </blockquote> </pre>
</table> </table> </table> </table> </table> </font> </font> </font>'''

__UNDEF__ = []                          # a special sentinel object
def small(text):
    if text:
        return '<small>' + text + '</small>'
    else:
        return ''

def strong(text):
    if text:
        return '<strong>' + text + '</strong>'
    else:
        return ''

def grey(text):
    if text:
        return '<font color="#909090">' + text + '</font>'
    else:
        return ''

def lookup(name, frame, locals):
    """Find the value for a given name in the given environment."""
    if name in locals:
        return 'local', locals[name]
    if name in frame.f_globals:
        return 'global', frame.f_globals[name]
    if '__builtins__' in frame.f_globals:
        builtins = frame.f_globals['__builtins__']
        if type(builtins) is type({}):
            if name in builtins:
                return 'builtin', builtins[name]
        else:
            if hasattr(builtins, name):
                return 'builtin', getattr(builtins, name)
    return None, __UNDEF__

def scanvars(reader, frame, locals):
    """Scan one logical line of Python and look up values of variables used."""
    import tokenize, keyword
    vars, lasttoken, parent, prefix, value = [], None, None, '', __UNDEF__
    for ttype, token, start, end, line in tokenize.generate_tokens(reader):
        if ttype == tokenize.NEWLINE: break
        if ttype == tokenize.NAME and token not in keyword.kwlist:
            if lasttoken == '.':
                if parent is not __UNDEF__:
                    value = getattr(parent, token, __UNDEF__)
                    vars.append((prefix + token, prefix, value))
            else:
                where, value = lookup(token, frame, locals)
                vars.append((token, where, value))
        elif token == '.':
            prefix += lasttoken + '.'
            parent = value
        else:
            parent, prefix = None, ''
        lasttoken = token
    return vars

def html((etype, evalue, etb), context=5):
    """Return a nice HTML document describing a given traceback."""
    import os, types, time, traceback, linecache, inspect, pydoc

    if type(etype) is types.ClassType:
        etype = etype.__name__
    pyver = 'Python ' + sys.version.split()[0] + ': ' + sys.executable
    date = time.ctime(time.time())
    head = '<body bgcolor="#f0f0f8">' + pydoc.html.heading(
        '<big><big>%s</big></big>' %
        strong(pydoc.html.escape(str(etype))),
        '#ffffff', '#6622aa', pyver + '<br>' + date) + '''
<p>A problem occurred in a Python script.  Here is the sequence of
function calls leading up to the error, in the order they occurred.</p>'''

    indent = '<tt>' + small('&nbsp;' * 5) + '&nbsp;</tt>'
    frames = []
    records = inspect.getinnerframes(etb, context)
    for frame, file, lnum, func, lines, index in records:
        if file:
            file = os.path.abspath(file)
            link = '<a href="file://%s">%s</a>' % (file, pydoc.html.escape(file))
        else:
            file = link = '?'
        args, varargs, varkw, locals = inspect.getargvalues(frame)
        call = ''
        if func != '?':
            call = 'in ' + strong(func) + \
                inspect.formatargvalues(args, varargs, varkw, locals,
                    formatvalue=lambda value: '=' + pydoc.html.repr(value))

        highlight = {}
        def reader(lnum=[lnum]):
            highlight[lnum[0]] = 1
            try: return linecache.getline(file, lnum[0])
            finally: lnum[0] += 1
        vars = scanvars(reader, frame, locals)

        rows = ['<tr><td bgcolor="#d8bbff">%s%s %s</td></tr>' %
                ('<big>&nbsp;</big>', link, call)]
        if index is not None:
            i = lnum - index
            for line in lines:
                num = small('&nbsp;' * (5-len(str(i))) + str(i)) + '&nbsp;'
                line = '<tt>%s%s</tt>' % (num, pydoc.html.preformat(line))
                if i in highlight:
                    rows.append('<tr><td bgcolor="#ffccee">%s</td></tr>' % line)
                else:
                    rows.append('<tr><td>%s</td></tr>' % grey(line))
                i += 1

        done, dump = {}, []
        for name, where, value in vars:
            if name in done: continue
            done[name] = 1
            if value is not __UNDEF__:
                if where in ('global', 'builtin'):
                    name = ('<em>%s</em> ' % where) + strong(name)
                elif where == 'local':
                    name = strong(name)
                else:
                    name = where + strong(name.split('.')[-1])
                dump.append('%s&nbsp;= %s' % (name, pydoc.html.repr(value)))
            else:
                dump.append(name + ' <em>undefined</em>')

        rows.append('<tr><td>%s</td></tr>' % small(grey(', '.join(dump))))
        frames.append('''
<table width="100%%" cellspacing=0 cellpadding=0 border=0>
%s</table>''' % '\n'.join(rows))

    exception = ['<p>%s: %s' % (strong(pydoc.html.escape(str(etype))),
                                pydoc.html.escape(str(evalue)))]
    if isinstance(evalue, BaseException):
        for name in dir(evalue):
            if name[:1] == '_': continue
            value = pydoc.html.repr(getattr(evalue, name))
            exception.append('\n<br>%s%s&nbsp;=\n%s' % (indent, name, value))

    import traceback
    return head + ''.join(frames) + ''.join(exception) + '''


<!-- The above is a description of an error in a Python program, formatted
     for a Web browser because the 'cgitb' module was enabled.  In case you
     are not reading this in a Web browser, here is the original traceback:

%s
-->
''' % pydoc.html.escape(
          ''.join(traceback.format_exception(etype, evalue, etb)))

def text((etype, evalue, etb), context=5):
    """Return a plain text document describing a given traceback."""
    import os, types, time, traceback, linecache, inspect, pydoc

    if type(etype) is types.ClassType:
        etype = etype.__name__
    pyver = 'Python ' + sys.version.split()[0] + ': ' + sys.executable
    date = time.ctime(time.time())
    head = "%s\n%s\n%s\n" % (str(etype), pyver, date) + '''
A problem occurred in a Python script.  Here is the sequence of
function calls leading up to the error, in the order they occurred.
'''

    frames = []
    records = inspect.getinnerframes(etb, context)
    for frame, file, lnum, func, lines, index in records:
        file = file and os.path.abspath(file) or '?'
        args, varargs, varkw, locals = inspect.getargvalues(frame)
        call = ''
        if func != '?':
            call = 'in ' + func + \
                inspect.formatargvalues(args, varargs, varkw, locals,
                    formatvalue=lambda value: '=' + pydoc.text.repr(value))

        highlight = {}
        def reader(lnum=[lnum]):
            highlight[lnum[0]] = 1
            try: return linecache.getline(file, lnum[0])
            finally: lnum[0] += 1
        vars = scanvars(reader, frame, locals)

        rows = [' %s %s' % (file, call)]
        if index is not None:
            i = lnum - index
            for line in lines:
                num = '%5d ' % i
                rows.append(num+line.rstrip())
                i += 1

        done, dump = {}, []
        for name, where, value in vars:
            if name in done: continue
            done[name] = 1
            if value is not __UNDEF__:
                if where == 'global': name = 'global ' + name
                elif where != 'local': name = where + name.split('.')[-1]
                dump.append('%s = %s' % (name, pydoc.text.repr(value)))
            else:
                dump.append(name + ' undefined')

        rows.append('\n'.join(dump))
        frames.append('\n%s\n' % '\n'.join(rows))

    exception = ['%s: %s' % (str(etype), str(evalue))]
    if isinstance(evalue, BaseException):
        for name in dir(evalue):
            value = pydoc.text.repr(getattr(evalue, name))
            exception.append('\n%s%s = %s' % (" "*4, name, value))

    import traceback
    return head + ''.join(frames) + ''.join(exception) + '''

The above is a description of an error in a Python program.  Here is
the original traceback:

%s
''' % ''.join(traceback.format_exception(etype, evalue, etb))

class Hook:
    """A hook to replace sys.excepthook that shows tracebacks in HTML."""

    def __init__(self, display=1, logdir=None, context=5, file=None,
                 format="html"):
        self.display = display          # send tracebacks to browser if true
        self.logdir = logdir            # log tracebacks to files if not None
        self.context = context          # number of source code lines per frame
        self.file = file or sys.stdout  # place to send the output
        self.format = format

    def __call__(self, etype, evalue, etb):
        self.handle((etype, evalue, etb))

    def handle(self, info=None):
        info = info or sys.exc_info()
        if self.format == "html":
            self.file.write(reset())

        formatter = (self.format=="html") and html or text
        plain = False
        try:
            doc = formatter(info, self.context)
        except:                         # just in case something goes wrong
            import traceback
            doc = ''.join(traceback.format_exception(*info))
            plain = True

        if self.display:
            if plain:
                doc = doc.replace('&', '&amp;').replace('<', '&lt;')
                self.file.write('<pre>' + doc + '</pre>\n')
            else:
                self.file.write(doc + '\n')
        else:
            self.file.write('<p>A problem occurred in a Python script.\n')

        if self.logdir is not None:
            import os, tempfile
            suffix = ['.txt', '.html'][self.format=="html"]
            (fd, path) = tempfile.mkstemp(suffix=suffix, dir=self.logdir)
            try:
                file = os.fdopen(fd, 'w')
                file.write(doc)
                file.close()
                msg = '<p> %s contains the description of this error.' % path
            except:
                msg = '<p> Tried to save traceback to %s, but failed.' % path
            self.file.write(msg + '\n')
        try:
            self.file.flush()
        except: pass

handler = Hook().handle
def enable(display=1, logdir=None, context=5, format="html"):
    """Install an exception handler that formats tracebacks as HTML.

    The optional argument 'display' can be set to 0 to suppress sending the
    traceback to the browser, and 'logdir' can be set to a directory to cause
    tracebacks to be written to files there."""
    sys.excepthook = Hook(display=display, logdir=logdir,
                          context=context, format=format)
Summary ✨

This code provides a way to display Python exceptions as HTML pages when an exception occurs, allowing for easy debugging and logging of errors. It can be installed by calling the enable function with optional arguments to control whether the output is displayed in the browser or logged to files. The output includes the error message, stack trace, and source code surrounding the error location.
Tech Fingerprint

Standard Library: OS Interaction
Alerts (19)

'def' Ensure functions have docstrings for documentation
41 47 53 129 214 271
'type(' Use isinstance() for type checking instead of type()
67 101 193
'isinstance(' Overuse may indicate design issues; consider polymorphism
170 243
Complexity hotspot; lines 232 to 234 (total complexity: 3)
232 233 234
'global' Avoid global variables; use function parameters or class attributes for better scope management
233
'except:' Avoid catching all exceptions; specify exception types to catch only expected errors
280 303 308
'open(' Use 'with open()' to ensure Files are properly closed
299