Raise warning in Python without interrupting program

Question

I am trying to raise a Warning in Python without making the program crash   stop   interrupt   I use the following simple function to check if the user passed a non-zero number to it  If so  the program should warn them  but continue as per normal  It should work like the code below  but should use class Warning    Error   or Exception   instead of printing the warning out manually   def is zero i      if i    0       print  OK     else       print  WARNING  the input is 0      return i   If I use the code below and pass 0 to the function  the program crashes and the value is never returned  Instead  I want the program to continue normally and just inform the user that he passed 0 to the function   def is zero i      if i    0       print  OK     else       raise Warning  the input is 0       return i   I want to be able to test that a warning has been thrown testing it by unittest  If I simply print the message out  I am not able to test it with assertRaises in unittest

User · Accepted Answer

You shouldn t raise the warning  you should be using warnings module  By raising it you re generating error  rather than warning

User · Answer

import warnings warnings warn  Warning           Message     See the python documentation  here

User · Answer

By default  unlike an exception  a warning doesn t interrupt   After import warnings  it is possible to specify a Warnings class when generating a warning  If one is not specified  it is literally UserWarning by default    gt  gt  gt  warnings warn  This is a default warning     lt string gt  1  UserWarning  This is a default warning    To simply use a preexisting class instead  e g  DeprecationWarning    gt  gt  gt  warnings warn  This is a particular warning    DeprecationWarning   lt string gt  1  DeprecationWarning  This is a particular warning    Creating a custom warning class is similar to creating a custom exception class    gt  gt  gt  class MyCustomWarning UserWarning           pass          warnings warn  This is my custom warning    MyCustomWarning    lt string gt  1  MyCustomWarning  This is my custom warning    For testing  consider assertWarns or assertWarnsRegex     As an alternative  especially for standalone applications  consider the logging module  It can log messages having a level of debug  info  warning  error  etc  Log messages having a level of warning or higher are by default printed to stderr

[python] Raise warning in Python without interrupting program

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