When you just want to do a try-except without handling the exception, how do you do it in Python?
Is the following the right way to do it?
try:
shutil.rmtree(path)
except:
pass
This question is related to
python
exception
try-except
In Python, we handle exceptions similar to other language, but the difference is some syntax difference, for example,
try:
#Your code in which exception can occur
except <here we can put in a particular exception name>:
# We can call that exception here also, like ZeroDivisionError()
# now your code
# We can put in a finally block also
finally:
# Your code...
For completeness:
>>> def divide(x, y):
... try:
... result = x / y
... except ZeroDivisionError:
... print("division by zero!")
... else:
... print("result is", result)
... finally:
... print("executing finally clause")
Also note that you can capture the exception like this:
>>> try:
... this_fails()
... except ZeroDivisionError as err:
... print("Handling run-time error:", err)
...and re-raise the exception like this:
>>> try:
... raise NameError('HiThere')
... except NameError:
... print('An exception flew by!')
... raise
...examples from the python tutorial.
try:
doSomething()
except Exception:
pass
else:
stuffDoneIf()
TryClauseSucceeds()
FYI the else clause can go after all exceptions and will only be run if the code in the try doesn't cause an exception.
I needed to ignore errors in multiple commands and fuckit did the trick
import fuckit
@fuckit
def helper():
print('before')
1/0
print('after1')
1/0
print('after2')
helper()
When you just want to do a try catch without handling the exception, how do you do it in Python?
This will help you to print what the exception is:( i.e. try catch without handling the exception and print the exception.)
import sys
try:
doSomething()
except:
print "Unexpected error:", sys.exc_info()[0]
It's generally considered best-practice to only catch the errors you are interested in. In the case of shutil.rmtree it's probably OSError:
>>> shutil.rmtree("/fake/dir")
Traceback (most recent call last):
[...]
OSError: [Errno 2] No such file or directory: '/fake/dir'
If you want to silently ignore that error, you would do:
try:
shutil.rmtree(path)
except OSError:
pass
Why? Say you (somehow) accidently pass the function an integer instead of a string, like:
shutil.rmtree(2)
It will give the error "TypeError: coercing to Unicode: need string or buffer, int found" - you probably don't want to ignore that, which can be difficult to debug.
If you definitely want to ignore all errors, catch Exception rather than a bare except: statement. Again, why?
Not specifying an exception catches every exception, including the SystemExit exception which for example sys.exit() uses:
>>> try:
... sys.exit(1)
... except:
... pass
...
>>>
Compare this to the following, which correctly exits:
>>> try:
... sys.exit(1)
... except Exception:
... pass
...
shell:~$
If you want to write ever better behaving code, the OSError exception can represent various errors, but in the example above we only want to ignore Errno 2, so we could be even more specific:
import errno
try:
shutil.rmtree(path)
except OSError as e:
if e.errno != errno.ENOENT:
# ignore "No such file or directory", but re-raise other errors
raise
How to properly ignore Exceptions?
There are several ways of doing this.
However, the choice of example has a simple solution that does not cover the general case.
Instead of
try:
shutil.rmtree(path)
except:
pass
Do this:
shutil.rmtree(path, ignore_errors=True)
This is an argument specific to shutil.rmtree. You can see the help on it by doing the following, and you'll see it can also allow for functionality on errors as well.
>>> import shutil
>>> help(shutil.rmtree)
Since this only covers the narrow case of the example, I'll further demonstrate how to handle this if those keyword arguments didn't exist.
Since the above only covers the narrow case of the example, I'll further demonstrate how to handle this if those keyword arguments didn't exist.
You can import the suppress context manager:
from contextlib import suppress
But only suppress the most specific exception:
with suppress(FileNotFoundError):
shutil.rmtree(path)
You will silently ignore a FileNotFoundError:
>>> with suppress(FileNotFoundError):
... shutil.rmtree('bajkjbkdlsjfljsf')
...
>>>
From the docs:
As with any other mechanism that completely suppresses exceptions, this context manager should be used only to cover very specific errors where silently continuing with program execution is known to be the right thing to do.
Note that suppress and FileNotFoundError are only available in Python 3.
If you want your code to work in Python 2 as well, see the next section:
When you just want to do a try/except without handling the exception, how do you do it in Python?
Is the following the right way to do it?
try : shutil.rmtree ( path ) except : pass
For Python 2 compatible code, pass is the correct way to have a statement that's a no-op. But when you do a bare except:, that's the same as doing except BaseException: which includes GeneratorExit, KeyboardInterrupt, and SystemExit, and in general, you don't want to catch those things.
In fact, you should be as specific in naming the exception as you can.
Here's part of the Python (2) exception hierarchy, and as you can see, if you catch more general Exceptions, you can hide problems you did not expect:
BaseException
+-- SystemExit
+-- KeyboardInterrupt
+-- GeneratorExit
+-- Exception
+-- StopIteration
+-- StandardError
| +-- BufferError
| +-- ArithmeticError
| | +-- FloatingPointError
| | +-- OverflowError
| | +-- ZeroDivisionError
| +-- AssertionError
| +-- AttributeError
| +-- EnvironmentError
| | +-- IOError
| | +-- OSError
| | +-- WindowsError (Windows)
| | +-- VMSError (VMS)
| +-- EOFError
... and so on
You probably want to catch an OSError here, and maybe the exception you don't care about is if there is no directory.
We can get that specific error number from the errno library, and reraise if we don't have that:
import errno
try:
shutil.rmtree(path)
except OSError as error:
if error.errno == errno.ENOENT: # no such file or directory
pass
else: # we had an OSError we didn't expect, so reraise it
raise
Note, a bare raise raises the original exception, which is probably what you want in this case. Written more concisely, as we don't really need to explicitly pass with code in the exception handling:
try:
shutil.rmtree(path)
except OSError as error:
if error.errno != errno.ENOENT: # no such file or directory
raise
I usually just do:
try:
doSomething()
except:
_ = ""
First I quote the answer of Jack o'Connor from this thread. The referenced thread got closed so I write here:
"There's a new way to do this coming in Python 3.4:
from contextlib import suppress
with suppress(Exception):
# your code
Here's the commit that added it: http://hg.python.org/cpython/rev/406b47c64480
And here's the author, Raymond Hettinger, talking about this and all sorts of other Python hotness: https://youtu.be/OSGv2VnC0go?t=43m23s
My addition to this is the Python 2.7 equivalent:
from contextlib import contextmanager
@contextmanager
def ignored(*exceptions):
try:
yield
except exceptions:
pass
Then you use it like in Python 3.4:
with ignored(Exception):
# your code
When you just want to do a try catch without handling the exception, how do you do it in Python?
It depends on what you mean by "handling."
If you mean to catch it without taking any action, the code you posted will work.
If you mean that you want to take action on an exception without stopping the exception from going up the stack, then you want something like this:
try:
do_something()
except:
handle_exception()
raise #re-raise the exact same exception that was thrown
Source: Stackoverflow.com