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#
# Zope Public License (ZPL) Version 1.0
# -------------------------------------
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# "This product includes software developed by Digital Creations
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##############################################################################
import string, sys, traceback
from cStringIO import StringIO
from DT_Util import ParseError,parse_params,render_blocks
from DT_Util import namespace,InstanceDict
from DT_Return import DTReturn
class Try:
"""Zope DTML Exception handling
usage:
<!--#try-->
<!--#except SomeError AnotherError-->
<!--#except YetAnotherError-->
<!--#except-->
<!--#else-->
<!--#/try-->
or:
<!--#try-->
<!--#finally-->
<!--#/try-->
The DTML try tag functions quite like Python's try command.
The contents of the try tag are rendered. If an exception is raised,
then control switches to the except blocks. The first except block to
match the type of the error raised is rendered. If an except block has
no name then it matches all raised errors.
The try tag understands class-based exceptions, as well as string-based
exceptions. Note: the 'raise' tag raises string-based exceptions.
Inside the except blocks information about the error is available via
three variables.
'error_type' -- This variable is the name of the exception caught.
'error_value' -- This is the caught exception's value.
'error_tb' -- This is a traceback for the caught exception.
The optional else block is rendered when no exception occurs in the
try block. Exceptions in the else block are not handled by the preceding
except blocks.
The try..finally form specifies a `cleanup` block, to be rendered even
when an exception occurs. Note that any rendered result is discarded if
an exception occurs in either the try or finally blocks. The finally block
is only of any use if you need to clean up something that will not be
cleaned up by the transaction abort code.
The finally block will always be called, wether there was an exception in
the try block or not, or wether or not you used a return tag in the try
block. Note that any output of the finally block is discarded if you use a
return tag in the try block.
If an exception occurs in the try block, and an exception occurs in the
finally block, or you use the return tag in that block, any information
about that first exception is lost. No information about the first
exception is available in the finally block. Also, if you use a return tag
in the try block, and an exception occurs in the finally block or you use
a return tag there as well, the result returned in the try block will be
lost.
Original version by Jordan B. Baker.
Try..finally and try..else implementation by Martijn Pieters.
"""
name = 'try'
blockContinuations = 'except', 'else', 'finally'
finallyBlock=None
elseBlock=None
def __init__(self, blocks):
tname, args, section = blocks[0]
self.args = parse_params(args)
self.section = section.blocks
# Find out if this is a try..finally type
if len(blocks) == 2 and blocks[1][0] == 'finally':
self.finallyBlock = blocks[1][2].blocks
# This is a try [except]* [else] block.
else:
# store handlers as tuples (name,block)
self.handlers = []
defaultHandlerFound = 0
for tname,nargs,nsection in blocks[1:]:
if tname == 'else':
if not self.elseBlock is None:
raise ParseError, (
'No more than one else block is allowed',
self.name)
self.elseBlock = nsection.blocks
elif tname == 'finally':
raise ParseError, (
'A try..finally combination cannot contain '
'any other else, except or finally blocks',
self.name)
else:
if not self.elseBlock is None:
raise ParseError, (
'The else block should be the last block '
'in a try tag', self.name)
for errname in string.split(nargs):
self.handlers.append((errname,nsection.blocks))
if string.strip(nargs)=='':
if defaultHandlerFound:
raise ParseError, (
'Only one default exception handler '
'is allowed', self.name)
else:
defaultHandlerFound = 1
self.handlers.append(('',nsection.blocks))
def render(self, md):
if (self.finallyBlock is None):
return self.render_try_except(md)
else:
return self.render_try_finally(md)
def render_try_except(self, md):
result = ''
# first we try to render the first block
try:
result = render_blocks(self.section, md)
except DTReturn:
raise
except:
# but an error occurs.. save the info.
t,v = sys.exc_info()[:2]
if type(t)==type(''):
errname = t
else:
errname = t.__name__
handler = self.find_handler(t)
if handler is None:
# we didn't find a handler, so reraise the error
raise
# found the handler block, now render it
try:
f=StringIO()
traceback.print_exc(100,f)
error_tb=f.getvalue()
ns = namespace(md, error_type=errname, error_value=v,
error_tb=error_tb)[0]
md._push(InstanceDict(ns,md))
return render_blocks(handler, md)
finally:
md._pop(1)
else:
# No errors have occured, render the optional else block
if (self.elseBlock is None):
return result
else:
return result + render_blocks(self.elseBlock, md)
def render_try_finally(self, md):
result = ''
# first try to render the first block
try:
result = render_blocks(self.section, md)
# Then handle finally block
finally:
result = result + render_blocks(self.finallyBlock, md)
return result
def find_handler(self,exception):
"recursively search for a handler for a given exception"
if type(exception)==type(''):
for e,h in self.handlers:
if exception==e or e=='':
return h
else:
return None
for e,h in self.handlers:
if e==exception.__name__ or e=='' or self.match_base(exception,e):
return h
return None
def match_base(self,exception,name):
for base in exception.__bases__:
if base.__name__==name or self.match_base(base,name):
return 1
return None
__call__ = render
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