Suppose I have a class with a string instance attribute. Should I initialize this attribute with "" value or None? Is either okay?
def __init__(self, mystr="") self.mystr = mystr
def __init__(self, mystr=None) self.mystr = mystr
Edit: What I thought is that if I use "" as an initial value, I "declare" a variable to be of string type. And then I won't be able to assign any other type to it later. Am I right?
Edit: I think it's important to note here, that my suggestion was WRONG. And there is no problem to assign another type to a variable. I liked a comment of S.Lott: "Since nothing in Python is "declared", you're not thinking about this the right way."
If not having a value has a meaning in your program (e.g. an optional value), you should use None. That's its purpose anyway.
If the value must be provided by the caller of __init__, I would recommend not to initialize it.
If "" makes sense as a default value, use it.
In Python the type is deduced from the usage. Hence, you can change the type by just assigning a value of another type.
>>> x = None >>> print type(x) <type 'NoneType'> >>> x = "text" >>> print type(x) <type 'str'> >>> x = 42 >>> print type(x) <type 'int'>
None is used to indicate "not set", whereas any other value is used to indicate a "default" value.
Hence, if your class copes with empty strings and you like it as a default value, use "". If your class needs to check if the variable was set at all, use None.
Notice that it doesn't matter if your variable is a string initially. You can change it to any other type/value at any other moment.