python - Catch multiple exceptions in one line (except block)

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Top 5 Answer for python - Catch multiple exceptions in one line (except block)

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100

From Python Documentation:

An except clause may name multiple exceptions as a parenthesized tuple, for example

except (IDontLikeYouException, YouAreBeingMeanException) as e:     pass 

Or, for Python 2 only:

except (IDontLikeYouException, YouAreBeingMeanException), e:     pass 

Separating the exception from the variable with a comma will still work in Python 2.6 and 2.7, but is now deprecated and does not work in Python 3; now you should be using as.

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88

How do I catch multiple exceptions in one line (except block)

Do this:

try:     may_raise_specific_errors(): except (SpecificErrorOne, SpecificErrorTwo) as error:     handle(error) # might log or have some other default behavior... 

The parentheses are required due to older syntax that used the commas to assign the error object to a name. The as keyword is used for the assignment. You can use any name for the error object, I prefer error personally.

Best Practice

To do this in a manner currently and forward compatible with Python, you need to separate the Exceptions with commas and wrap them with parentheses to differentiate from earlier syntax that assigned the exception instance to a variable name by following the Exception type to be caught with a comma.

Here's an example of simple usage:

import sys  try:     mainstuff() except (KeyboardInterrupt, EOFError): # the parens are necessary     sys.exit(0) 

I'm specifying only these exceptions to avoid hiding bugs, which if I encounter I expect the full stack trace from.

This is documented here: https://docs.python.org/tutorial/errors.html

You can assign the exception to a variable, (e is common, but you might prefer a more verbose variable if you have long exception handling or your IDE only highlights selections larger than that, as mine does.) The instance has an args attribute. Here is an example:

import sys  try:     mainstuff() except (KeyboardInterrupt, EOFError) as err:      print(err)     print(err.args)     sys.exit(0) 

Note that in Python 3, the err object falls out of scope when the except block is concluded.

Deprecated

You may see code that assigns the error with a comma. This usage, the only form available in Python 2.5 and earlier, is deprecated, and if you wish your code to be forward compatible in Python 3, you should update the syntax to use the new form:

import sys  try:     mainstuff() except (KeyboardInterrupt, EOFError), err: # don't do this in Python 2.6+     print err     print err.args     sys.exit(0) 

If you see the comma name assignment in your codebase, and you're using Python 2.5 or higher, switch to the new way of doing it so your code remains compatible when you upgrade.

The suppress context manager

The accepted answer is really 4 lines of code, minimum:

try:     do_something() except (IDontLikeYouException, YouAreBeingMeanException) as e:     pass 

The try, except, pass lines can be handled in a single line with the suppress context manager, available in Python 3.4:

from contextlib import suppress  with suppress(IDontLikeYouException, YouAreBeingMeanException):      do_something() 

So when you want to pass on certain exceptions, use suppress.

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76

From Python documentation -> 8.3 Handling Exceptions:

A try statement may have more than one except clause, to specify handlers for different exceptions. At most one handler will be executed. Handlers only handle exceptions that occur in the corresponding try clause, not in other handlers of the same try statement. An except clause may name multiple exceptions as a parenthesized tuple, for example:

except (RuntimeError, TypeError, NameError):     pass 

Note that the parentheses around this tuple are required, because except ValueError, e: was the syntax used for what is normally written as except ValueError as e: in modern Python (described below). The old syntax is still supported for backwards compatibility. This means except RuntimeError, TypeError is not equivalent to except (RuntimeError, TypeError): but to except RuntimeError as TypeError: which is not what you want.

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65

If you frequently use a large number of exceptions, you can pre-define a tuple, so you don't have to re-type them many times.

#This example code is a technique I use in a library that connects with websites to gather data  ConnectErrs  = (URLError, SSLError, SocketTimeoutError, BadStatusLine, ConnectionResetError)  def connect(url, data):     #do connection and return some data     return(received_data)  def some_function(var_a, var_b, ...):     try: o = connect(url, data)     except ConnectErrs as e:         #do the recovery stuff     blah #do normal stuff you would do if no exception occurred 

NOTES:

  1. If you, also, need to catch other exceptions than those in the pre-defined tuple, you will need to define another except block.

  2. If you just cannot tolerate a global variable, define it in main() and pass it around where needed...

vote vote

55

One of the way to do this is..

try:    You do your operations here;    ...................... except(Exception1[, Exception2[,...ExceptionN]]]):    If there is any exception from the given exception list,     then execute this block.    ...................... else:    If there is no exception then execute this block.  

and another way is to create method which performs task executed by except block and call it through all of the except block that you write..

try:    You do your operations here;    ...................... except Exception1:     functionname(parameterList) except Exception2:     functionname(parameterList) except Exception3:     functionname(parameterList) else:    If there is no exception then execute this block.   def functionname( parameters ):    //your task..    return [expression] 

I know that second one is not the best way to do this, but i'm just showing number of ways to do this thing.

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