How to convert Nonetype to int or string

Question

I ve got an Nonetype value x  it s generally a number  but could be None  I want to divide it by a number  but Python raises   TypeError  int   argument must be a string or a number  not  NoneType    How can I solve this

User · Answer

This can happen if you forget to return a value from a function  it then returns None  Look at all places where you are assigning to that variable  and see if one of them is a function call where the function lacks a return statement

User · Answer

You should check to make sure the value is not None before trying to perform any calculations on it   my value   None if my value is not None      print int my value    2   Note  my value was intentionally set to None to prove the code works and that the check is being performed

User · Answer

I was having the same problem using the python email functions  Below is the code I was trying to retrieve email subject into a variable   This works fine for most emails and the variable populates   If you receive an email from Yahoo or the like and the sender did no fill out the subject line Yahoo does not create a subject line in the email and you get a NoneType returned from the function   Martineau provided a correct answer as well as Soviut   IMO Soviut s answer is more concise from a programming stand point  not necessarily from a Python one  Here is some code to show the technique   import sys  email  email Utils   afile   open sys argv 1    r       m   email message from file afile      subject   m  subject      Soviut s Concise test for unset variable   if subject is None           subject     NO SUBJECT      Alternative way to test for No Subject created in email  Thanks for NoneThing Yahoo    try          if len subject     0              subject     NO SUBJECT    except TypeError          subject     NO SUBJECT    print subject  afile close

User · Answer

int value or 0    This will use 0 in the case when you provide any value that Python considers False  such as None  0          etc  Since 0 is False  you should only use 0 as the alternative value  otherwise you will find your 0s turning into that value    int 0 if value is None else value    This replaces only None with 0  Since we are testing for None specifically  you can use some other value as the replacement

User · Answer

In Python 3 you can use the  or  keyword too  This way   foo   bar or 0 foo2   bar or

User · Answer

A common  quot Pythonic quot  way to handle this kind of situation is known as EAFP for  quot It s easier to ask forgiveness than permission quot   Which usually means writing code that assumes everything is fine  but then wrapping it with a try   except block to handle things   just in case   it s not  Here s that coding style applied to your problem  try      my value   int my value  except TypeError      my value   0    or whatever you want to do  answer   my value   divisor  Or perhaps the even simpler and slightly faster  try      answer   int my value    divisor except TypeError      answer   0  The inverse and more traditional approach is known as LBYL which stands for  quot Look before you leap quot  is what  Soviut and some of the others have suggested  For additional coverage of this topic see my answer and associated comments to the question Determine whether a key is present in a dictionary elsewhere on this site  One potential problem with EAFP is that it can hide the fact that something is wrong with some other part of your code or third-party module you re using  especially when the exceptions frequently occur  and therefore aren t really  quot exceptional quot  cases at all

User · Answer

In some situations it is helpful to have a function to convert None to int zero   def nz value                Convert None to int zero else return value               if value    None          return 0     return value

User · Answer

In one of the comments  you say      Somehow I got an Nonetype value  it supposed to be an int  but it s now a Nonetype object   If it s your code  figure out how you re getting None when you expect a number and stop that from happening   If it s someone else s code  find out the conditions under which it gives None and determine a sensible value to use for that  with the usual conditional code   result   could return none x   if result is None      result   DEFAULT VALUE      or even     if x    THING THAT RESULTS IN NONE      result   DEFAULT VALUE else      result   could return none x    But it won t return None  because we ve restricted the domain    There s no reason to automatically use 0 here     solutions that depend on the  false -ness of None assume you will want this  The DEFAULT VALUE  if it even exists  completely depends on your code s purpose

User · Answer

That TypeError only appears when you try to pass int   None  which is the only NoneType value  as far as I know    I would say that your real goal should not be to convert NoneType to int or str  but to figure out where why you re getting None instead of a number as expected  and either fix it or handle the None properly

User · Answer

I ve successfully used int x or 0  for this type of error  so long as None should equate to 0 in the logic  Note that this will also resolve to 0 in other cases where testing x returns False  e g  empty list  set  dictionary or zero length string  Sorry  Kindall already gave this answer

[python] How to convert Nonetype to int or string?

Examples related to python