What is a NoneType object

Question

I m getting this error when I run my python script   TypeError  cannot concatenate  str  and  NoneType  objects   I m pretty sure the  str  means string  but I dont know what a  NoneType  object is  My script craps out on the second line  I know the first one works because the commands from that line are in my asa as I would expect  At first I thought it may be because I m using variables and user input inside send command   Everything in  CAPS  are variables  everything in  lower case  is input from  parser add option  options   I m using pexpect  and optparse  send command child  SNMPGROUPCMD   group   V3PRIVCMD  send command child  SNMPSRVUSRCMD   snmpuser   group   V3AUTHCMD   snmphmac   snmpauth   PRIVCMD   snmpencrypt   snmppriv

User · Answer

Your error s occurring due to something like this   gt  gt  gt  None    hello world  Traceback  most recent call last     File   lt stdin gt    line 1  in  lt module gt  TypeError  unsupported operand type s  for     NoneType  and  str         Python s None object is roughly equivalent to null  nil  etc  in other languages

User · Answer

NoneType is the type for the None object  which is an object that indicates no value  None is the return value of functions that  don t return anything   It is also a common default return value for functions that search for something and may or may not find it  for example  it s returned by re search when the regex doesn t match  or dict get when the key has no entry in the dict  You cannot add None to strings or other objects   One of your variables is None  not a string  Maybe you forgot to return in one of your functions  or maybe the user didn t provide a command-line option and optparse gave you None for that option s value  When you try to add None to a string  you get that exception   send command child  SNMPGROUPCMD   group   V3PRIVCMD    One of group or SNMPGROUPCMD or V3PRIVCMD has None as its value

User · Answer

One of the variables has not been given any value  thus it is a NoneType  You ll have to look into why this is  it s probably a simple logic error on your part

User · Answer

In the error message  instead of telling you that you can t concatenate two objects by showing their values  a string and None in this example   the Python interpreter tells you this by showing the types of the objects that you tried to concatenate  The type of every string is str while the type of the single None instance is called NoneType   You normally do not need to concern yourself with NoneType  but in this example it is necessary to know that type None     NoneType

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A nonetype is the type of a None   See the docs here  https   docs python org 2 library types html types NoneType

User · Answer

For the sake of defensive programming  objects should be checked against nullity before using   if obj is None    or  if obj is not None

User · Answer

In Python  to represent the absence of a value  you can use the None value types NoneType None

User · Answer

It means you re trying to concatenate a string with something that is None   None is the  null  of Python  and NoneType is its type   This code will raise the same kind of error    gt  gt  gt  bar    something   gt  gt  gt  foo   None  gt  gt  gt  print foo   bar TypeError  cannot concatenate  str  and  NoneType  objects

User · Answer

NoneType is simply the type of the None singleton    gt  gt  gt  type None   lt type  NoneType  gt    From the latter link above      None      The sole value of the type NoneType  None is frequently used to represent the absence of a value  as when default arguments are not passed to a function  Assignments to None are illegal and raise a SyntaxError     In your case  it looks like one of the items you are trying to concatenate is None  hence your error

[python] What is a 'NoneType' object?

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