How do I change a string to a python type

Question

If I have a string which is the same as a python data type and I would like to check if another variable is that type how would I do it? Example below.

dtype = 'str'
x = 'hello'
bool = type(x) == dtype

The above obviously returns False but I'd like to check that type('hello') is a string.

• Karl Knechtel: What counts as "a Python data type"? Do you care about user-defined classes, for example?
• Karl Knechtel: If you have a set number of types, why not just create an explicit mapping?

Answer 1

You can use eval:

bool = type(x) is eval(dtype)

but beware, eval will execute any python code, so if you're taking dtype as user input, they can execute their own code in this line.

Answer 2

Don't write :

bool = type(x) == dtype

because dtype is a variabe It is in the form of a string , not logical !!

you should be entered a statement to check is str or no

Also, the string in Python is an object so to call it write : str not write dtype = 'str',exemple :

type(x) == str

i fixed your code and just try this :

x = 'hello'
if type(x) == str:
 print(True)
else:
 print(False)

It's a simple code but there are other shortcuts that come from Python

try that and good day for coding !!

Answer 3

If your code actually looks like the example you showed and dtype isn't coming from user input, then also keep in mind that str (as a value in Python) is a valid object which represents the string type. Consider

dtype = str
x = 'hello'
print(isinstance(x, dtype))

str is a value like any other and can be assigned to variables. No eval magic required.

• national440: dtype is being read in from a csv so I don't have control over the variable in that way

Answer 4

I think the best way to do this verification is to use isinstance, like:

isinstance(x, str) # returns True

From the docs:

isinstance(object, classinfo)

Return True if the object argument is an instance of the classinfo argument, or of a (direct, indirect or virtual) subclass thereof. If object is not an object of the given type, the function always returns False. If classinfo is a tuple of type objects (or recursively, other such tuples), return True if object is an instance of any of the types. If classinfo is not a type or tuple of types and such tuples, a TypeError exception is raised.

https://docs.python.org/3/library/functions.html#isinstance

Answer 5

One solution is using .__name__ as follows:

dtype = 'str'
x = 'hello'
bool = type(x).__name__ == dtype