Checking Variable Types in Python

In Python, it’s often necessary to check the type of a variable. This can be useful for ensuring that your code behaves as expected or for handling different types of input data. In this tutorial, we’ll explore how to check if a variable is a string.

Using isinstance()

The recommended way to check the type of an object in Python is by using the isinstance() function. This function takes two arguments: the object you want to check and the type you’re looking for. For example:

my_string = "Hello, World!"
if isinstance(my_string, str):
    print("The variable is a string.")

This code will output: "The variable is a string."

Using type()

Another way to check the type of an object is by using the type() function. This function returns the type of the object, which you can then compare to the desired type. For example:

my_string = "Hello, World!"
if type(my_string) == str:
    print("The variable is a string.")

This code will also output: "The variable is a string."

Important differences between isinstance() and type()

While both isinstance() and type() can be used to check the type of an object, there’s an important difference between them. The type() function only checks if the object is exactly of the specified type, whereas isinstance() also checks if the object is an instance of a subclass.

For example:

class MyString(str):
    pass

my_string = MyString("Hello, World!")
print(type(my_string) == str)  # Output: False
print(isinstance(my_string, str))  # Output: True

As you can see, isinstance() correctly identifies MyString as a subclass of str, while type() does not.

Cross-version compatibility

If you’re writing code that needs to work on both Python 2 and Python 3, you might need to use the six library, which provides a way to check for string types in a cross-version compatible way:

import six

if isinstance(value, six.string_types):
    print("The variable is a string.")

This code will work correctly on both Python 2 and Python 3.

Conclusion

In conclusion, checking the type of a variable in Python can be done using either isinstance() or type(). However, isinstance() is generally recommended because it takes subclasses into account. By using these functions, you can write more robust code that handles different types of input data correctly.