Develop Reference

How to jump to same function again after exception in python

I have below script which generates report for large size data.
Due to large size data request call times out.
I have added exception to handle this situation which works fine to get keep script running.
Issue I am having is after exception it goes to next project and skips the projects where it timed out.
I want it to start from same project again.
How can I achieve this ?
if __name__ = ‘__main__’
for project in AllProjectData['value']:
try:
project_name = project['name']
** code to be executed
except:
requests.ConnectionError,
requests.exceptions.ReadTimeout,
requests.exceptions.Timeout,
requests.exceptions.ConnectTimeout
continue

You are catching exceptions in a very odd way. I've never seen it done like this. I believe this code is catching all exceptions. For example:
try:
1/0
except:
ZeroDivisionError
pass
Works fine, but so does (it should raise IndexError):
try:
a = []
print(a[1])
except:
ZeroDivisionError
pass
So you shouldn't write except statements this way. What you should have is something along the lines:
success = False
while not success:
try:
# Your execution code
except (requests.ConnectionError,
requests.exceptions.ReadTimeout,
requests.exceptions.Timeout,
requests.exceptions.ConnectTimeout):
continue
else:
success = True
Also you should try and not put so much code in your except statement as it is confusing as to what you're trying to catch and where. Also, you're completely missing some possibilities like a KeyError when there's no id field in project and others.

Try this -
def myfunc():
# Write the code given in question completely
# Then add this in your except statement
except:
requests.ConnectionError,
requests.exceptions.ReadTimeout,
requests.exceptions.Timeout,
requests.exceptions.ConnectTimeout
# Call your function so that it will jump back to the same function
myfunc()
# You don't need continue keyword because it jumps to the same function

The simplest way would be to use a while loop with a counter variable. Let me demonstrate:
i = 0
while i < len(AllProjectData['value']):
try:
project = AllProjectData['value'][i]
# code to be executed
i += 1 # increment counter on success
except:
requests.ConnectionError,
requests.exceptions.ReadTimeout,
requests.exceptions.Timeout,
requests.exceptions.ConnectTimeout
continue
This way, you will go to the next project only if work on the previous project was executed, as the loop variable is incremented only in the try block.
Note: I have assumed that your iterable is indexable. If it's not, just pass it inside the list() constructor.

Count exception thrown in Python [duplicate]

Is it possible to tell if there was an exception once you're in the finally clause? Something like:
try:
funky code
finally:
if ???:
print('the funky code raised')
I'm looking to make something like this more DRY:
try:
funky code
except HandleThis:
# handle it
raised = True
except DontHandleThis:
raised = True
raise
else:
raised = False
finally:
logger.info('funky code raised %s', raised)
I don't like that it requires to catch an exception, which you don't intend to handle, just to set a flag.
Since some comments are asking for less "M" in the MCVE, here is some more background on the use-case. The actual problem is about escalation of logging levels.
The funky code is third party and can't be changed.
The failure exception and stack trace does not contain any useful diagnostic information, so using logger.exception in an except block is not helpful here.
If the funky code raised then some information which I need to see has already been logged, at level DEBUG. We do not and can not handle the error, but want to escalate the DEBUG logging because the information needed is in there.
The funky code does not raise, most of the time. I don't want to escalate logging levels for the general case, because it is too verbose.
Hence, the code runs under a log capture context (which sets up custom handlers to intercept log records) and some debug info gets re-logged retrospectively:
try:
with LogCapture() as log:
funky_code() # <-- third party badness
finally:
# log events are buffered in memory. if there was an exception,
# emit everything that was captured at a WARNING level
for record in log.captured:
if <there was an exception>:
log_fn = mylogger.warning
else:
log_fn = getattr(mylogger, record.levelname.lower())
log_fn(record.msg, record.args)

Using a contextmanager
You could use a custom contextmanager, for example:
class DidWeRaise:
__slots__ = ('exception_happened', ) # instances will take less memory
def __enter__(self):
return self
def __exit__(self, exc_type, exc_val, exc_tb):
# If no exception happened the `exc_type` is None
self.exception_happened = exc_type is not None
And then use that inside the try:
try:
with DidWeRaise() as error_state:
# funky code
finally:
if error_state.exception_happened:
print('the funky code raised')
It's still an additional variable but it's probably a lot easier to reuse if you want to use it in multiple places. And you don't need to toggle it yourself.
Using a variable
In case you don't want the contextmanager I would reverse the logic of the trigger and toggle it only in case no exception has happened. That way you don't need an except case for exceptions that you don't want to handle. The most appropriate place would be the else clause that is entered in case the try didn't threw an exception:
exception_happened = True
try:
# funky code
except HandleThis:
# handle this kind of exception
else:
exception_happened = False
finally:
if exception_happened:
print('the funky code raised')
And as already pointed out instead of having a "toggle" variable you could replace it (in this case) with the desired logging function:
mylog = mylogger.WARNING
try:
with LogCapture() as log:
funky_code()
except HandleThis:
# handle this kind of exception
else:
# In case absolutely no exception was thrown in the try we can log on debug level
mylog = mylogger.DEBUG
finally:
for record in log.captured:
mylog(record.msg, record.args)
Of course it would also work if you put it at the end of your try (as other answers here suggested) but I prefer the else clause because it has more meaning ("that code is meant to be executed only if there was no exception in the try block") and may be easier to maintain in the long run. Although it's still more to maintain than the context manager because the variable is set and toggled in different places.
Using sys.exc_info (works only for unhandled exceptions)
The last approach I want to mention is probably not useful for you but maybe useful for future readers who only want to know if there's an unhandled exception (an exception that was not caught in any except block or has been raised inside an except block). In that case you can use sys.exc_info:
import sys
try:
# funky code
except HandleThis:
pass
finally:
if sys.exc_info()[0] is not None:
# only entered if there's an *unhandled* exception, e.g. NOT a HandleThis exception
print('funky code raised')

raised = True
try:
funky code
raised = False
except HandleThis:
# handle it
finally:
logger.info('funky code raised %s', raised)
Given the additional background information added to the question about selecting a log level, this seems very easily adapted to the intended use-case:
mylog = WARNING
try:
funky code
mylog = DEBUG
except HandleThis:
# handle it
finally:
mylog(...)

You can easily assign your caught exception to a variable and use it in the finally block, eg:
>>> x = 1
>>> error = None
>>> try:
... x.foo()
... except Exception as e:
... error = e
... finally:
... if error is not None:
... print(error)
...
'int' object has no attribute 'foo'

Okay, so what it sounds like you actually just want to either modify your existing context manager, or use a similar approach: logbook actually has something called a FingersCrossedHandler that would do exactly what you want. But you could do it yourself, like:
#contextmanager
def LogCapture():
# your existing buffer code here
level = logging.WARN
try:
yield
except UselessException:
level = logging.DEBUG
raise # Or don't, if you just want it to go away
finally:
# emit logs here
Original Response
You're thinking about this a bit sideways.
You do intend to handle the exception - you're handling it by setting a flag. Maybe you don't care about anything else (which seems like a bad idea), but if you care about doing something when an exception is raised, then you want to be explicit about it.
The fact that you're setting a variable, but you want the exception to continue on means that what you really want is to raise your own specific exception, from the exception that was raised:
class MyPkgException(Exception): pass
class MyError(PyPkgException): pass # If there's another exception type, you can also inherit from that
def do_the_badness():
try:
raise FileNotFoundError('Or some other code that raises an error')
except FileNotFoundError as e:
raise MyError('File was not found, doh!') from e
finally:
do_some_cleanup()
try:
do_the_badness()
except MyError as e:
print('The error? Yeah, it happened')
This solves:
Explicitly handling the exception(s) that you're looking to handle
Making the stack traces and original exceptions available
Allowing your code that's going to handle the original exception somewhere else to handle your exception that's thrown
Allowing some top-level exception handling code to just catch MyPkgException to catch all of your exceptions so it can log something and exit with a nice status instead of an ugly stack trace

If it was me, I'd do a little re-ordering of your code.
raised = False
try:
# funky code
except HandleThis:
# handle it
raised = True
except Exception as ex:
# Don't Handle This
raise ex
finally:
if raised:
logger.info('funky code was raised')
I've placed the raised boolean assignment outside of the try statement to ensure scope and made the final except statement a general exception handler for exceptions that you don't want to handle.
This style determines if your code failed. Another approach might me to determine when your code succeeds.
success = False
try:
# funky code
success = True
except HandleThis:
# handle it
pass
except Exception as ex:
# Don't Handle This
raise ex
finally:
if success:
logger.info('funky code was successful')
else:
logger.info('funky code was raised')

If exception happened --> Put this logic in the exception block(s).
If exception did not happen --> Put this logic in the try block after the point in code where the exception can occur.
Finally blocks should be reserved for "cleanup actions," according to the Python language reference. When finally is specified the interpreter proceeds in the except case as follows: Exception is saved, then the finally block is executed first, then lastly the Exception is raised.

Avoiding try-except nesting

Given a file of unknown file type, I'd like to open that file with one of a number of handlers. Each of the handlers raises an exception if it cannot open the file.
I would like to try them all and if none succeeds, raise an exception.
The design I came up with is
filename = 'something.something'
try:
content = open_data_file(filename)
handle_data_content(content)
except IOError:
try:
content = open_sound_file(filename)
handle_sound_content(content)
except IOError:
try:
content = open_image_file(filename)
handle_image_content(content)
except IOError:
...
This cascade doesn't seem to be the right way to do it.
Any suggestions?

Maybe you can group all the handlers and evaluate them in a for loop raising an exception at the end if none succeeded. You can also hang on to the raised exception to get some of the information back out of it as shown here:
filename = 'something.something'
handlers = [(open_data_file, handle_data_context),
(open_sound_file, handle_sound_content),
(open_image_file, handle_image_content)
]
for o, h in handlers:
try:
o(filename)
h(filename)
break
except IOError as e:
pass
else:
# Raise the exception we got within. Also saves sub-class information.
raise e

Is checking entirely out of the question?
>>> import urllib
>>> from mimetypes import MimeTypes
>>> guess = MimeTypes()
>>> path = urllib.pathname2url(target_file)
>>> opener = guess.guess_type(path)
>>> opener
('audio/ogg', None)
I know try/except and eafp is really popular in Python, but there are times when a foolish consistency will only interfere with the task at hand.
Additionally, IMO a try/except loop may not necessarily break for the reasons you expect, and as others have pointed out you're going to need to report the errors in a meaningful way if you want to see what's really happening as you try to iterate over file openers until you either succeed or fail. Either way, there's introspective code being written: to dive into the try/excepts and get a meaningful one, or reading the file path and using a type checker, or even just splitting the file name to get the extension... in the face of ambiguity, refuse the temptation to guess.

Like the others, I also recommend using a loop, but with tighter try/except scopes.
Plus, it's always better to re-raise the original exception, in order to preserve extra info about the failure, including traceback.
openers_handlers = [ (open_data_file, handle_data_context) ]
def open_and_handle(filename):
for i, (opener, handler) in enumerate(openers_handlers):
try:
f = opener(filename)
except IOError:
if i >= len(openers_handlers) - 1:
# all failed. re-raise the original exception
raise
else:
# try next
continue
else:
# successfully opened. handle:
return handler(f)

You can use Context Managers:
class ContextManager(object):
def __init__(self, x, failure_handling):
self.x = x
self.failure_handling = failure_handling
def __enter__(self):
return self.x
def __exit__(self, exctype, excinst, exctb):
if exctype == IOError:
if self.failure_handling:
fn = self.failure_handling.pop(0)
with ContextManager(fn(filename), self.failure_handling) as context:
handle_data_content(context)
return True
filename = 'something.something'
with ContextManager(open_data_file(filename), [open_sound_file, open_image_file]) as content:
handle_data_content(content)

How to continue python script loop even though IOError?

I have a program which request info from the twitter API, and from time to time I get an error:
IOError: [Errno socket error] [Errno 54] Connection reset by peer
I want to know how can I keep my script running (looping). I know that this has something to do with:
try:
except IOError:
but I can not figure it out.

The simpler structure is like this:
my_while_or_for_loop:
some_code_here_maybe
try:
my_code_or_function_that_sometimes_fails()
except IOError:
pass # or some code to clean things that went wrong or to log the failure
some_more_code_here_maybe
You want to read the docs
The full construction can be more complex and includes try/except/else/finally.
From an example in docs:
>>> def divide(x, y):
... try:
... result = x / y
... except ZeroDivisionError:
... print "division by zero!"
... else:
... print "result is", result
... finally:
... print "executing finally clause"

Here is is documentationabout exceptions...
Simply, if a code block have possibility to cause some known errors (like input output error) in some conditions, you define an try-exceptblock to handle such errors. That will make your script keep runnung and let you execute diffrent code blocks according to diffrent error status.... Like:
try:
<do something>
except IOError:
<an input-output error occured, do this...>
except ValueError:
<we got something diffrent then we expected, do something diffrent>
except LookupError:
pass # we do not need to handle this one, so just kkeep going...
except:
<some diffrent error occured, do somethnig more diffrent>
If you simply do nothing and continue, you can use pass, like:
try:
<do something>
except:
pass

The part you're missing is pass. That is a simple no-op expression, which exists because Python can have no empty blocks.
The longer explanation:
What you need to do is to catch the IOError exception being thrown, and ignore it (possibly logging it and such) using pass.
To do that you need to wrap the code that can fail in a try and except block, like this:
try:
<code that can fail>
except IOError:
pass
What this does is explicitly ignore IOErrors, while not ignoring others. If you want to ignore all exceptions, simply remove the IOError part so the line says except:.
You should really read the Python tutorial, specifically the section about error handling.

Try this:
try:
<do something - you code here>
except IOError: pass

Or why not:
with ignored(IOError):
<code that can fail>

Python: How to tell the for loop to continue from a function?

Sometimes I need the following pattern within a for loop. At times more than once in the same loop:
try:
# attempt to do something that may diversely fail
except Exception as e:
logging.error(e)
continue
Now I don't see a nice way to wrap this in a function as it can not return continue:
def attempt(x):
try:
raise random.choice((ValueError, IndexError, TypeError))
except Exception as e:
logging.error(e)
# continue # syntax error: continue not properly in loop
# return continue # invalid syntax
return None # this sort of works
If I return None than I could:
a = attempt('to do something that may diversely fail')
if not a:
continue
But I don't feel that does it the justice. I want to tell the for loop to continue (or fake it) from within attempt function.

Python already has a very nice construct for doing just this and it doesn't use continue:
for i in range(10):
try:
r = 1.0 / (i % 2)
except Exception, e:
print(e)
else:
print(r)
I wouldn't nest any more than this, though, or your code will soon get very ugly.
In your case I would probably do something more like this as it is far easier to unit test the individual functions and flat is better than nested:
#!/usr/bin/env python
def something_that_may_raise(i):
return 1.0 / (i % 2)
def handle(e):
print("Exception: " + str(e))
def do_something_with(result):
print("No exception: " + str(result))
def wrap_process(i):
try:
result = something_that_may_raise(i)
except ZeroDivisionError, e:
handle(e)
except OverflowError, e:
handle(e) # Realistically, this will be a different handler...
else:
do_something_with(result)
for i in range(10):
wrap_process(i)
Remember to always catch specific exceptions. If you were not expecting a specific exception to be thrown, it is probably not safe to continue with your processing loop.
Edit following comments:
If you really don't want to handle the exceptions, which I still think is a bad idea, then catch all exceptions (except:) and instead of handle(e), just pass. At this point wrap_process() will end, skipping the else:-block where the real work is done, and you'll go to the next iteration of your for-loop.
Bear in mind, Errors should never pass silently.

The whole idea of exceptions is that they work across multiple levels of indirection, i.e., if you have an error (or any other exceptional state) deep inside your call hierarchy, you can still catch it on a higher level and handle it properly.
In your case, say you have a function attempt() which calls the functions attempt2() and attempt3() down the call hierarchy, and attempt3() may encounter an exceptional state which should cause the main loop to terminate:
class JustContinueException(Exception):
pass
for i in range(0,99):
try:
var = attempt() # calls attempt2() and attempt3() in turn
except JustContinueException:
continue # we don't need to log anything here
except Exception, e:
log(e)
continue
foo(bar)
def attempt3():
try:
# do something
except Exception, e:
# do something with e, if needed
raise # reraise exception, so we catch it downstream
You can even throw a dummy exception yourself, that would just cause the loop to terminate, and wouldn't even be logged.
def attempt3():
raise JustContinueException()

Apart from the context I just want to answer the question in a brief fashion. No, a function cannot continue a loop it may be called in. That is because it has no information about this context. Also, it would raise a whole new class of questions like what shall happen if that function is called without a surrounding loop to handle that continue?
BUT a function can signal by various means that it wants the caller to continue any loop it currently performs. One means of course is the return value. Return False or None to signal this for example. Another way of signaling this is to raise a special Exception:
class ContinuePlease(Exception): pass
def f():
raise ContinuePlease()
for i in range(10):
try:
f()
except ContinuePlease:
continue

Maybe you want to do continuations? You could go and look at how Eric Lippert explains them (if you are ready to have your mind blown, but in Python it could look a bit like this:
def attempt(operation, continuation):
try:
operation()
except:
log('operation failed!')
continuation()
Inside your loop you could do:
attempt(attempt_something, lambda: foo(bar)) # attempt_something is a function

You could use this:
for l in loop:
attempt() and foo(bar)
but you should make sure attempt() returns True or False.
Really, though, Johnsyweb's answer is probably better.

Think that you are mapping foo on all items where attempt worked. So attempt is a filter and it's easy to write this as a generator:
def attempted( items ):
for item in items:
try:
yield attempt( item )
except Exception, e:
log(e)
print [foo(bar) for bar in attempted( items )]

I wouldn't normally post a second answer, but this is an alternative approach if you really don't like my first answer.
Remember that a function can return a tuple.
#!/usr/bin/env python
def something_that_mail_fail(i):
failed = False
result = None
try:
result = 1.0 / (i % 4)
except:
failed = True # But we don't care
return failed, result
for i in range(20):
failed, result = something_that_mail_fail(i)
if failed:
continue
for rah in ['rah'] * 3:
print(rah)
print(result)
I maintain that try ... except ... else is the way to go, and you shouldn't silently ignore errors though. Caveat emptor and all that.

Try the for loop outside the try, except block
This answer had Python 3.4 in mind however there are better ways in newer versions. Here is my suggestion
import sys
if '3.4' in sys.version:
from termcolor import colored
def list_attributes(module_name):
'''Import the module before calling this func on it.s '''
for index, method in enumerate(dir(module_name)):
try:
method = str(method)
module = 'email'
expression = module + '.' + method
print('*' * len(expression), '\n')
print( str(index).upper() + '. ',colored( expression.upper(), 'red'),
' ', eval( expression ).dir() , '...' , '\n'2 )
print('' * len(expression), '\n')
print( eval( expression + '.doc' ), '\n'*4,
'END OF DESCRIPTION FOR: ' + expression.upper(), '\n'*4)
except (AttributeError, NameError):
continue
else:
pass
finally:
pass

Edit: Removed all that stupidity I said...
The final answer was to rewrite the whole thing, so that I don't need to code like that.