How to Check if a Variable is a String - Python

The goal is to check if a variable is a string in Python to ensure it can be handled as text. Since Python variables can store different types of data such as numbers, lists or text, it’s important to confirm the type before performing operations meant only for strings. For example, if a variable contains the value "hello", we may want to check whether it is a string or not. Let's explore different methods to do this efficiently.

Using isinstance()

isinstance() is the most efficient way to check if a variable is of a specific type. It supports inheritance, meaning it will return True even if the variable is an instance of a subclass of str.

a = "hello"

if isinstance(a, str):
    print("Yes")
else:
    print("No")

Yes

Explanation: isinstance() function checks if a is an instance of the str class or its subclass. If true, it prints "Yes", otherwise, it prints "No".

Using type()

type() method checks the exact type of a variable. It returns True only if the variable is strictly a string (str) and not a subclass. It's simple and works well when you want a strict match.

a = "hello"

if type(a) == str:
    print("Yes")
else:
    print("No")

Yes

Explanation: type() function checks if a is exactly of the str type. If true, it prints "Yes" otherwise, it prints "No".

Using try- except

Instead of checking the type directly, this method tries to use a string method like .lower() and sees if it works. If it fails, Python will raise an AttributeError, meaning the variable is not a string. This follows Python’s “try it and see” style and also called duck typing.

a = "hello"

try:
    a.lower()
    print("Yes")
except AttributeError:
    print("No")

Yes

Explanation: This code attempts to call the lower() method on a. If a is a string, the method will work, and it prints "Yes". If a does not have a lower() method (e.g., it's not a string), it raises an AttributeError, and the code prints "No".

Using re module

This way uses regular expressions to check if the variable is a string and optionally matches a specific pattern. It’s a bit of an overkill just for type checking but can be helpful when you also want to validate the content of the string.

import re

a = "hello"

if isinstance(a, str) and re.fullmatch(r".*", a):
    print("Yes")
else:
    print("No")

Yes

Explanation: If a is a string using isinstance(a, str). If true, it then uses re.fullmatch(r".*", a) to confirm that a matches the pattern for any string since .* matches any string .