I have this code using a While True with a try catch. The final else statement is always being executed when the 'try' is successful and I'd like to understand why - I think I'm not understanding the program flow correctly.
while True:
try:
subprocess.call(["wget", "-O", "splunk-8.0.1-6db836e2fb9e-Linux-x86_64.tgz", "https://www.splunk.com/bin/splunk/DownloadActivityServlet?architecture=x86_64&platform=linux&version=8.0.1&product=splunk&filename=splunk-8.0.1-6db836e2fb9e-Linux-x86_64.tgz&wget=true"])
print("successfully downloaded splunk enterprise")
time.sleep(2)
except OSError as e:
if e.errno == 2:
print(e)
print("wget doesn't seem to be installed")
time.sleep(2)
print("attempting to install wget")
time.sleep(2)
subprocess.call(["yum", "install", "wget"])
else:
print(e)
print("unknown error response, exiting...")
break
else:
print("something else went wrong while trying to download splunk")
break
based on python documentation, try-except can take an optional else statement:
The try … except statement has an optional else clause, which, when present, must follow all except clauses. It is useful for code that must be executed if the try clause does not raise an exception.
so based on this, your else statement will run if codes in try doesn't raise any exception!
what you want is another except clause that catches a general exceptation, so you just need to replace else with except:
while True:
try:
subprocess.call(["wget", "-O", "splunk-8.0.1-6db836e2fb9e-Linux-x86_64.tgz", "https://www.splunk.com/bin/splunk/DownloadActivityServlet?architecture=x86_64&platform=linux&version=8.0.1&product=splunk&filename=splunk-8.0.1-6db836e2fb9e-Linux-x86_64.tgz&wget=true"])
print("successfully downloaded splunk enterprise")
time.sleep(2)
except OSError as e:
if e.errno == 2:
print(e)
print("wget doesn't seem to be installed")
time.sleep(2)
print("attempting to install wget")
time.sleep(2)
subprocess.call(["yum", "install", "wget"])
else:
print(e)
print("unknown error response, exiting...")
break
except:
print("something else went wrong while trying to download splunk")
break
The else clause of a try executes if the code inside the try did not throw an exception. If you want to catch any exception, use except without specifying an exception class:
except:
print("something else went wrong while trying to download splunk")
break
However, consider just omitting this piece of code. As it is currently written, it doesn't tell you what went wrong. If you remove these lines, you will get an error message that tells you what happened and on which line the error occurred.
From here:
The try … except statement has an optional else clause, which, when present, must follow all except clauses. It is useful for code that must be executed if the try clause does not raise an exception.
So the else clause will run if the code within the try block runs successfully.
Related
I am making a Reddit bot using PRAW and the code gives me the error that the exception is not iterable. Here is a simplification of my code:
try:
#something with praw that isn't relevant
except Exception as e: #this except error catches the APIexception, APIexpections in PRAW are a wide field of exceptions that dont't always have the same solution, so I scan the text for the error I'm looking for.
print(e)
if "keyword thats in the error" in e:
#fix the problem with the specific error
else:
print("Unkown APIExpection error")
This works fine for me, but when I run this code:
try:
#something
except Exception as e:
for character in e:
print(character)
#I also tried this
try:
#something
except Exception as e:
for character in str(e):
print(character)
#None of the above work but this is my actual code and what I need to do, anything that gets the above to work should work here too, I'm just letting you know this so that I don't get any other errors I have to ask another question for.
try:
#something
except Exception as e:
characterNum = 0
for character in e:
characterNum += 1
print(str(characterNum) + ": " + character)
It gives me a "TypeError: 'RedditAPIException' is not iterable", RedditAPIException can be ignore though as that's just the error I'm catching.
Convert the exception to string and then check in the if statement.
Change to => if "keyword thats in the error" in str(e):
if not ping_device(ip):
if not reboot_device(device_1)
logger.error("Unable to reboot.. Serious issue")
break
logger.info("HARD Rebooted")
if not ping_device(ip):
logger.error("Ping failed after hard reboot")
else:
logger.info("Pinged success after reboot")
else:
logger.info("Pinged")
logger.info("Reboot passed")
logger.info("Getting uptime")
sw_version_check = get_sw_version(ip)
check_upgrade()
:
:
:
:
Here is my piece of code. Now if the ping_device fn in the first line succeeds, I have no problem. The else part comes into the picture.
Now if my first line ping_device fails, I call a reboot_device fn. after reboot, I again call the ping function to check my device is online.
After the ping success after the reboot, I need to get going with the else part of the first if condition with sw_version_check, check_upgrade() and rest of code traverses as mentioned with :
Will my logic after ping failure continue with sw_version_chec and check_upgrade?
You could have some separate variable, say doUpgrade, initialized to False and set to True at any point(s) in the first section where you have determined you need an upgrade. Then test that variable to see if the upgrade code needs to be executed.
Try using exceptions, they help make this type of control flow easier to reason about and are more "Pythonic":
def reboot_device(device):
if not your_reboot_device_fn(device):
raise DeviceRebootError('Unrecoverable reboot error')
else:
pass # Or anything else you want to do on success.
def ping_device(ip, device, did_try_reboot=False):
if not your_ping_device_fn(ip):
if did_try_reboot:
raise DevicePingError('Ping failed after hard reboot')
else:
try:
reboot_device(device)
except DeviceRebootError as e:
logging.error(e)
raise
else:
logger.info("HARD Rebooted")
ping_device(ip, device, did_try_reboot=True)
else:
pass # Or anything else you want to do on success.
try:
ping_device(ip, device_1)
except DevicePingError as e:
logging.error(e)
# NOTE: DeviceRebootError isn't caught so it will end the program.
else:
logging.info('Pinged')
sw_version_check = get_sw_version(ip)
check_upgrade()
I'm a Python learner, trying to handle a few scenarios:
Reading a file.
Formatting Data.
Manipulating/Copying Data.
Writing a file.
So far, I have:
try:
# Do all
except Exception as err1:
print err1
#File Reading error/ File Not Present
except Exception as err2:
print err2
# Data Format is incorrect
except Exception as err3:
print err3
# Copying Issue
except Exception as err4:
print err4
# Permission denied for writing
The idea of implementing in this fashion is to catch the exact error for all different scenarios. I can do it in all separate try/except blocks.
Is this possible? And reasonable?
Your try blocks should be as minimal as possible, so
try:
# do all
except Exception:
pass
is not something you want to do.
The code in your example won't work as you expect it to, because in every except block you are catching the most general exception type Exception. In fact, only the first except block will ever be executed.
What you want to be doing is having multiple try/except blocks, each one responsible for as few things as possible and catching the most specific exception.
For example:
try:
# opening the file
except FileNotFoundException:
print('File does not exist')
exit()
try:
# writing to file
except PermissionError:
print('You do not have permission to write to this file')
exit()
However, sometimes it is appropriate to catch different types of exceptions, in the same except block or in several blocks.
try:
ssh.connect()
except (ConnectionRefused, TimeoutError):
pass
or
try:
ssh.connect()
except ConnectionRefused:
pass
except TimeoutError:
pass
As DeepSpace stated,
Your try blocks should be as minimal as possible.
If you want to achieve
try:
# do all
except Exception:
pass
Then you might as well do something like
def open_file(file):
retval = False
try:
# opening the file succesful?
retval = True
except FileNotFoundException:
print('File does not exist')
except PermissionError:
print('You have no permission.')
return retval
def crunch_file(file):
retval = False
try:
# conversion or whatever logical operation with your file?
retval = True
except ValueError:
print('Probably wrong data type?')
return retval
if __name__ == "__main__":
if open_file(file1):
open(file1)
if open_file(file2) and crunch_file(file2):
print('opened and crunched')
Yes this is possible.
Just say as example:
try:
...
except RuntimeError:
print err1
except NameError:
print err2
...
Just define the exact Error you want to intercept.
I have a python selenium script that runs through a loop like this...
for i, refcode in enumerate(refcode_list):
try:
source_checkrefcode()
except TimeoutException:
pass
csvWriter.writerow([refcode, 'error', timestamp])
If there is a problem during the source_checkrefcode then the script crashes with an error.
How can I add error handling to this loop so that it just moves to the next item instead of crashing?
You can add a check over exception message, below is the sample code for your understanding.
for i, refcode in enumerate(refcode_list):
try:
source_checkrefcode()
except Exception as e:
if 'particular message' in str(e):
# Do the following
# if you don't want to stop for loop then just continue
continue
I agree with Hassan's Answer. But if you use continue then you won't process any other block of code.
for i, refcode in enumerate(refcode_list):
try:
source_checkrefcode()
except Exception as e:
if 'particular message' in str(e):
# Do the following
# if you don't want to stop for loop then just continue
continue
# another code of block will skip. Use pass or continue as per your requirement.
You must understand the difference between pass and continue
Link
I am trying in Python.
try:
newbutton['roundcornerradius'] = buttondata['roundcornerradius']
buttons.append(newbutton)
buttons is a list. roundcornerradius is optional in buttondata.
Alas this gives
buttons.append(newbutton)
^ SyntaxError: invalid syntax
I just want to ignore the cases where roundcornerradius does not exist. I don't need any error reported.
why arent you using the except keyword
try:
newbutton['roundcornerradius'] = buttondata['roundcornerradius']
buttons.append(newbutton)
except:
pass
this will try the first part and if an error is thrown it will do the except part
you can also add the disered error you want to except a certain error like this
except AttributeError:
you can also get the excepted error by doing this:
except Exception,e: print str(e)
You should catch a try with exception:
try:
code may through exception
except (DesiredException):
in case of exception
Also you can use else with try if you need to populate new buttons only when try succeeds:
try:
newbutton['roundcornerradius'] = buttondata['roundcornerradius']
except KeyError:
pass
else:
buttons.append(newbutton)
single except: with no exception class defined will catch every exception raised which may not be desired in some cases.
Most probably you will get KeyError on your code but I am not sure.
See here for builtin exceptions:
http://docs.python.org/2/library/exceptions.html
You must close block with except or finally if using try.
try:
newbutton['roundcornerradius'] = buttondata['roundcornerradius']
except KeyError:
pass#omit raise if key 'roundcornerradius' does not exists
buttons.append(newbutton)
If you know default value for 'roundcornerradius' - you dont need no try ... except
newbutton['roundcornerradius'] = buttondata.get('roundcornerradius', DEFAULT_RADIUS)
buttons.append(newbutton)