How to print an exception in Python?

问题:

try:
    something here
except:
    print 'the whatever error occurred.'

How can I print the error/exception in my except: block?

回答1:

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)

回答2:

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

回答3:

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

回答4:

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

回答5:

(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.

回答6:

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"