How can I catch AttributeError from this line and print message to the user, let's say "you can't change class="post" "
I tried with try, except AttributeError, raise, print but it's always returning nothing.
That's what I did:
re.search() returns None if no position in the string matches the pattern. Check for None and raise an exception:
post_start = re.search('<div class="post">', html)
if post_start is None:
raise AttributeError('you can\'t change <div class="post">')
Related
For example I have script like this
def form_valid:
temp = form.save(commit=False)
try:
temp.contents = makecontents()
except:
messages.error(self.request, error)
return self.render_to_response(self.get_context_data(form=form))
messages.success(self.request, self.success_message)
return super().form_valid(form)
def makecontents():
if (if works well):
return "this is my contents"
else:
return "this is error!!"
So, my basic idea is when makecontents() success it returns the string s and set this as member of model instance.
However makecontents() failed , I want to return the error to form_valid.
So, maybe ,, I should change return "this is error!!" somehow..
Is it possible? , or my idea is wrong??
you could use anraise '<an Exception Type>("error message")' to raise an Error, and then except Exception as e: to get the exception message:
def makecontents(works_well):
try:
if (works_well):
return "this is my contents"
else:
raise SyntaxError("this is an error")
except Exception as e:
return str(e)
print(makecontents(works_well=False).__repr__())
output:
"this is an error"
try:
msg_json = json.loads(message_string)
if "task" in msg_json:
job_type = msg_json["task"]
return (job_type, msg_json)
logger.error(
"Could not parse message: must provide 'task' property",
extra={"message_string": message_string},
)
return empty
except Exception:
logger.exception(
"Error parsing JSON message. Did you accidentally double-escape it?",
extra={"message_string": message_string},
)
return empty
I have this code where i am trying to load some JSON formatted message string. After looking back at this piece of code i feel i maybe using try and catch in the wrong way and i was looking for suggestions as i am new to python and there may be cleaner approaches. There is no bug here but this is more for me to learn the "Cleaner" approach. As such i am open to all suggestions that explain the cleaner and more correct approach.
You could handle both of your error cases in catch blocks, which makes your "happy path" code a bit cleaner and neatly groups all the error handling in one place:
try:
msg_json = json.loads(message_string)
return (msg_json["task"], msg_json)
except KeyError:
logger.error(
"Could not parse message: must provide 'task' property",
extra={"message_string": message_string},
)
return empty
except Exception:
logger.exception(
"Error parsing JSON message. Did you accidentally double-escape it?",
extra={"message_string": message_string},
)
return empty
itemis a python dictionary
print item.get('body')
gives the following output in some cases:
"1211V1"
however, item.get('body') mostly has a unicode string of the format:
u'{"points_token_id":"327727a0-3909-4132-8fa2-ee45146add1e"}'
I needed to convert the above unicode string to a python dictionary. So I am doing this:
try:
body_dic = json.loads(item.get('body'))
body_string = ""
for body_item in body_dic.keys():
body_string += body_item + ": {'required': True, 'type': 'resource', 'value': " + str(body_dic.get('body_item')) + "\n\t\t\t\t"
except Exception as e:
print "futt gayaa"
print type(e).__name__
print e.args
body_string = item.get('body')
and then a bunch of code after this. So in the above the moment item.get('body') comes out to be "1211V1" a ValueError Exception should be raised and the execution flow should get into the except block. Am I right ?
It does not get raised however and the execution flow continues to go onto the next line which is :
for body_item in body_dic.keys():
and then the following exception gets raised:
AttributeError
("'unicode' object has no attribute 'keys'",)
which I get to know if I change the except block in the above to catch a generic exception as :
except Exception as e:
print "futt gayaa"
print type(e).__name__
print e.args
body_string = item.get('body')
Please help me understand this. In my opinion the moment the first exception gets raised (which in our case should be the ValueError Exception) the control flow should go into the catch block. Why does it go to the next line of code and then when the Attribute Exception gets raised does it get caught.
Assuming that, as you wrote
print item.get("body")
returns literally
"1211V1"
then the quotation marks are part of the string itself.
So you effectively calling
json.loads('"1211V1"')
where you are loading a JSON string literal--perfectly valid. Then, of course, you get an AttributeError for trying to call .keys() on a unicode object.
If you're using print to debug a problem it might mislead you in this way--you're better off often, if you really want to be sure what the object is that you're having trouble with, writing print(repr(obj)). In this case that would tell you that item.get("body") is u'"1211V1"'.
So your problem is that you have a sequence of dicts, whose attribute body is a JSON string. It may either be:
"1211V1"
or:
{
"points_token_id":"327727a0-3909-4132-8fa2-ee45146add1e"
}
This is, a JSON string or a JSON object. By json.loads()ing this string you are always getting a valid Python value, either a Python str or a Python dict, respectively. What you want to do is detect if its one or another:
json_body = json.loads(item['body'])
if type(json_body) is dict:
for key, value in json_body.items():
json_body[key] = {'required': True, 'type': 'resource', 'value': value}
body_string = json.dumps(json_body)
else:
pass # Handle the "1211V1"
I have a function with a try catch block where I have:
def testfunction():
try:
good = myfunction()
return good
except ExceptionOne:
error="Error ExceptionOne".
return error
except ExceptionTwo:
error="Error ExceptionTwo".
return error
except ExceptionThree:
error="Error ExceptionThree".
return error
Is there a way such that I could structure this in such a way where have a single return statement for all the exceptions?
What about something like:
def testfunction():
try:
good = myfunction() # or `return myfunction()` if the case is actually this simple
except (ExceptionOne, ExceptionTwo, ExceptionThree) as err:
error = 'Error %s' % err.__class__.__name__
return error
return good
Of course, I'm not exactly sure what the purpose of this is. Why not just let the exception propogate and handle it higher up? As it is, you need logic to check the return value to see if it's good or not anyway, I think it would be cleaner if that logic was bound up in exception handling rather than in type checking or string value checking ...
In my application users enter a url and I try to open the link and get the title of the page. But I realized that there can be many different kinds of errors, including unicode characters or newlines in titles and AttributeError and IOError. I first tried to catch each error, but now in case of a url fetch error I want to redirect to an error page where the user will enter the title manually. How do I catch all possible errors? This is the code I have now:
title = "title"
try:
soup = BeautifulSoup.BeautifulSoup(urllib.urlopen(url))
title = str(soup.html.head.title.string)
if title == "404 Not Found":
self.redirect("/urlparseerror")
elif title == "403 - Forbidden":
self.redirect("/urlparseerror")
else:
title = str(soup.html.head.title.string).lstrip("\r\n").rstrip("\r\n")
except UnicodeDecodeError:
self.redirect("/urlparseerror?error=UnicodeDecodeError")
except AttributeError:
self.redirect("/urlparseerror?error=AttributeError")
#https url:
except IOError:
self.redirect("/urlparseerror?error=IOError")
#I tried this else clause to catch any other error
#but it does not work
#this is executed when none of the errors above is true:
#
#else:
# self.redirect("/urlparseerror?error=some-unknown-error-caught-by-else")
UPDATE
As suggested by #Wooble in the comments I added try...except while writing the title to database:
try:
new_item = Main(
....
title = unicode(title, "utf-8"))
new_item.put()
except UnicodeDecodeError:
self.redirect("/urlparseerror?error=UnicodeDecodeError")
This works. Although the out-of-range character —is still in title according to the logging info:
***title: 7.2. re — Regular expression operations — Python v2.7.1 documentation**
Do you know why?
You can use except without specifying any type to catch all exceptions.
From the python docs http://docs.python.org/tutorial/errors.html:
import sys
try:
f = open('myfile.txt')
s = f.readline()
i = int(s.strip())
except IOError as (errno, strerror):
print "I/O error({0}): {1}".format(errno, strerror)
except ValueError:
print "Could not convert data to an integer."
except:
print "Unexpected error:", sys.exc_info()[0]
raise
The last except will catch any exception that has not been caught before (i.e. a Exception which is not of IOError or ValueError.)
You can use the top level exception type Exception, which will catch any exception that has not been caught before.
http://docs.python.org/library/exceptions.html#exception-hierarchy
try:
soup = BeautifulSoup.BeautifulSoup(urllib.urlopen(url))
title = str(soup.html.head.title.string)
if title == "404 Not Found":
self.redirect("/urlparseerror")
elif title == "403 - Forbidden":
self.redirect("/urlparseerror")
else:
title = str(soup.html.head.title.string).lstrip("\r\n").rstrip("\r\n")
except UnicodeDecodeError:
self.redirect("/urlparseerror?error=UnicodeDecodeError")
except AttributeError:
self.redirect("/urlparseerror?error=AttributeError")
#https url:
except IOError:
self.redirect("/urlparseerror?error=IOError")
except Exception, ex:
print "Exception caught: %s" % ex.__class__.__name__