My Python scripts crashes sometimes while reading the stats from a file (last edit time). Sometimes it works for days, sometimes it crashes every hour. I can’t reproduce the bug :(
I tried to solve it with try except but the script simply crashes
Fatal Python error: (pygame parachute) Segmentation Fault
Code:
try:
stat = os.stat(self.pathDB+""+fileName+".txt")
except OSError as e:
print("OS ERROR - : %s" % e)
return False
except Exception as e:
print("FATAL ERROR - TEST: %s" % e)
return False
Does anyone has an idea how to solve this?
How do I print the error/exception in the except: block?
try:
...
except:
print(exception)
For Python 2.6 and later and Python 3.x:
except Exception as e: print(e)
For Python 2.5 and earlier, use:
except Exception,e: print str(e)
The traceback module provides methods for formatting and printing exceptions and their tracebacks, e.g. this would print exception like the default handler does:
import traceback
try:
1/0
except Exception:
traceback.print_exc()
Output:
Traceback (most recent call last):
File "C:\scripts\divide_by_zero.py", line 4, in <module>
1/0
ZeroDivisionError: division by zero
In Python 2.6 or greater it's a bit cleaner:
except Exception as e: print(e)
In older versions it's still quite readable:
except Exception, e: print e
Python 3: logging
Instead of using the basic print() function, the more flexible logging module can be used to log the exception. The logging module offers a lot extra functionality, for example, logging messages...
into a given log file, or
with timestamps and additional information about where the logging happened.
For more information check out the official documentation.
Usage
Logging an exception can be done with the module-level function logging.exception() like so:
import logging
try:
1/0
except BaseException:
logging.exception("An exception was thrown!")
Output
ERROR:root:An exception was thrown!
Traceback (most recent call last):
File ".../Desktop/test.py", line 4, in <module>
1/0
ZeroDivisionError: division by zero
Notes
the function logging.exception() should only be called from an exception handler
the logging module should not be used inside a logging handler to avoid a RecursionError (thanks #PrakharPandey)
Alternative log-levels
It's also possible to log the exception with another log level but still show the exception details by using the keyword argument exc_info=True, like so:
logging.critical("An exception was thrown!", exc_info=True)
logging.error ("An exception was thrown!", exc_info=True)
logging.warning ("An exception was thrown!", exc_info=True)
logging.info ("An exception was thrown!", exc_info=True)
logging.debug ("An exception was thrown!", exc_info=True)
# or the general form
logging.log(level, "An exception was thrown!", exc_info=True)
Name and description only
Of course, if you don't want the whole traceback but only some specific information (e.g., exception name and description), you can still use the logging module like so:
try:
1/0
except BaseException as exception:
logging.warning(f"Exception Name: {type(exception).__name__}")
logging.warning(f"Exception Desc: {exception}")
Output
WARNING:root:Exception Name: ZeroDivisionError
WARNING:root:Exception Desc: division by zero
(I was going to leave this as a comment on #jldupont's answer, but I don't have enough reputation.)
I've seen answers like #jldupont's answer in other places as well. FWIW, I think it's important to note that this:
except Exception as e:
print(e)
will print the error output to sys.stdout by default. A more appropriate approach to error handling in general would be:
except Exception as e:
print(e, file=sys.stderr)
(Note that you have to import sys for this to work.) This way, the error is printed to STDERR instead of STDOUT, which allows for the proper output parsing/redirection/etc. I understand that the question was strictly about 'printing an error', but it seems important to point out the best practice here rather than leave out this detail that could lead to non-standard code for anyone who doesn't eventually learn better.
I haven't used the traceback module as in Cat Plus Plus's answer, and maybe that's the best way, but I thought I'd throw this out there.
In case you want to pass error strings, here is an example from Errors and Exceptions (Python 2.6)
>>> try:
... raise Exception('spam', 'eggs')
... except Exception as inst:
... print type(inst) # the exception instance
... print inst.args # arguments stored in .args
... print inst # __str__ allows args to printed directly
... x, y = inst # __getitem__ allows args to be unpacked directly
... print 'x =', x
... print 'y =', y
...
<type 'exceptions.Exception'>
('spam', 'eggs')
('spam', 'eggs')
x = spam
y = eggs
One has pretty much control on which information from the traceback to be displayed/logged when catching exceptions.
The code
with open("not_existing_file.txt", 'r') as text:
pass
would produce the following traceback:
Traceback (most recent call last):
File "exception_checks.py", line 19, in <module>
with open("not_existing_file.txt", 'r') as text:
FileNotFoundError: [Errno 2] No such file or directory: 'not_existing_file.txt'
Print/Log the full traceback
As others already mentioned, you can catch the whole traceback by using the traceback module:
import traceback
try:
with open("not_existing_file.txt", 'r') as text:
pass
except Exception as exception:
traceback.print_exc()
This will produce the following output:
Traceback (most recent call last):
File "exception_checks.py", line 19, in <module>
with open("not_existing_file.txt", 'r') as text:
FileNotFoundError: [Errno 2] No such file or directory: 'not_existing_file.txt'
You can achieve the same by using logging:
try:
with open("not_existing_file.txt", 'r') as text:
pass
except Exception as exception:
logger.error(exception, exc_info=True)
Output:
__main__: 2020-05-27 12:10:47-ERROR- [Errno 2] No such file or directory: 'not_existing_file.txt'
Traceback (most recent call last):
File "exception_checks.py", line 27, in <module>
with open("not_existing_file.txt", 'r') as text:
FileNotFoundError: [Errno 2] No such file or directory: 'not_existing_file.txt'
Print/log error name/message only
You might not be interested in the whole traceback, but only in the most important information, such as Exception name and Exception message, use:
try:
with open("not_existing_file.txt", 'r') as text:
pass
except Exception as exception:
print("Exception: {}".format(type(exception).__name__))
print("Exception message: {}".format(exception))
Output:
Exception: FileNotFoundError
Exception message: [Errno 2] No such file or directory: 'not_existing_file.txt'
Expanding off of the "except Exception as e:" solution here is a nice one liner which includes some additional info like the type of error and where it occurred.
try:
1/0
except Exception as e:
print(f"{type(e).__name__} at line {e.__traceback__.tb_lineno} of {__file__}: {e}")
Output:
ZeroDivisionError at line 48 of /Users/.../script.py: division by zero
Try this
try:
print("Hare Krishna!")
except Exception as er:
print(er)
One liner error raising can be done with assert statements if that's what you want to do. This will help you write statically fixable code and check errors early.
assert type(A) is type(""), "requires a string"
I would recommend using a try-except statement. Also, rather than using a print statement, a logging exception logs a message with level ERROR on the logger, which I find is more effective than a print output. This method should only be called from an exception handler, as it is here:
import logging
try:
*code goes here*
except BaseException:
logging.exception("*Error goes here*")
There's good documentation on this python page if you want to learn more about logging and debugging.
I am using the below code for downloading files from a ftp server.But I am getting an error [Errno 2] No such file or directory:, but the file present in the server and I can able download it via terminal. Can anyone help me!!
import ftplib
import os
remotpath='folder/subfolder'
try:
ftpclient = ftplib.FTP('ftp.xxxx.com')
ftpclient.login('user', 'pass')
ftpclient.cwd(remotpath)
print "login succeessfull"
files = ftpclient.nlst()
for eachFile in files:
saveTo = os.path.join(remotpath,eachFile)
if (not os.path.exists(saveTo)):
try:
ftpclient.retrbinary('RETR ' + eachFile, open(saveTo, 'wb').write)
#logging.info('\tdownloaded ' + saveTo)
downloaded += 1
except BaseException as e:
print('\terror downloading inside first %s - %s' % (eachFile, e.__str__()))
except ftplib.error_perm:
print('\terror downloading inside second %s - %s' % (eachFile, ftplib.error_perm))
except Exception as e:
print e
Does the destination directory ./folder/subfolder exist?
If not you need to create it before downloading files. Either do so using your OS commands (mkdir), or in Python using os.makedirs() :
import os
try:
os.makedirs(remotpath)
except OSError as exception:
if exception.errno != errno.EEXIST:
raise
You can add it somewhere before the for loop.
On another issue, the order of you exception handlers means that all exceptions raised in the inner try block would be handled in the except BaseException statement. This means that ftplib.error_perm will be caught in that statement because BaseException is more general, and not in the ftplib.error_perm statement as you might expect.
You should reorder your except statements in order of increasing generality.
I'm trying to implement a method that returns an error whenever a certain directory does not exist.
Rather than doing raise OSError("Directory does not exist."), however, I want to use the builtint error message from OSError: OSError: [Errno 2] No such file or directory:. This is because I am raising the exception in the beginning of the method call, rather than later (which would invoke the same message from python, without any necessary raise).
Any pointers? (other than manually doing OSError("[Errno 2] No such file or directory: "))
import os
try:
open('foo')
except IOError as err:
print(err)
print(err.args)
print(err.filename)
produces
[Errno 2] No such file or directory: 'foo'
(2, 'No such file or directory')
foo
So, to generate an OSError with a similar message use
raise OSError(2, 'No such file or directory', 'foo')
To get the error message for a given error code, you might want to use os.strerror:
>>> os.strerror(2)
'No such file or directory'
Also, you might want to use errno module to use the standard abbreviations for those errors:
>>> errno.ENOENT
2
>>> os.strerror(errno.ENOENT)
'No such file or directory'
I think that "exception" is the Python language term for what you are calling "error". So use this term as you search for more information.
You might find it useful to read the Python Standard Library documentation, "6. Built-in Exceptions".
OSError is one of the built-in exceptions. It's defined in the "Built-in Exceptions" section, which adds, "The errno attribute is a numeric error code from errno, and the strerror attribute is the corresponding string, as would be printed by the C function perror(). See the module errno, which contains names for the error codes defined by the underlying operating system."
Running this code:
raise OSError(42, "my exception string", "no_such_file.dat")
gives me this result:
Traceback (most recent call last):
Line 1, in <module>
raise OSError(42, "my exception string", "no_such_file.dat")
OSError: [Errno 42] my exception string: 'no_such_file.dat'
So, I think your code could do something like:
raise OSError(2, "No such file or directory", filename)
I think the real problem here is that you are probably doing a bunch of checks beforehand instead of just trying.
try:
[CODE]
except Exception:
[HANDLING CODE]
is much better than:
if [SPECIAL CASE]:
[HANDLING CODE]
elif [special case]:
[SPECIAL CASE]
[CODE]
try:
# ...
except OSError:
raise OSError("your answer")
When trying to open a directory, an exception is thrown:
>>> try:
... open( '/' )
... except IOError, e:
... print e.filename
None
Is it possible (preferrably in python 2.3.4) for the handler of the exception to get the name of the directory from the exception object?
This is a bug in older versions of Python: http://bugs.python.org/issue4764
Supplying the open function with a mode, open('/', 'r'), might allow you to retrieve the filename via e.filename.