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How to Check if a Python Object Has a Specific Method

In Python, you often need to determine if an object has a particular method before attempting to call it.

This guide explains the correct and reliable way to check if an object has a specific method, using the hasattr() and callable() functions. We'll also briefly discuss why a simple try/except block is not sufficient for this task.

The most reliable way to check if an object has a specific method involves two steps:

  1. Check for attribute existence: Use hasattr(object, 'method_name') to see if the object has an attribute with the given name.

  2. Check for callability: Use callable(getattr(object, 'method_name')) to verify that the attribute is actually a callable method (and not, for example, a variable).

class Employee():
    def __init__(self, first, last):
        self.first = first
        self.last = last

    def get_name(self):
        return f'{self.first} {self.last}'

emp1 = Employee('Tom', 'Nolan')

if hasattr(emp1, 'get_name') and callable(getattr(emp1, 'get_name')):
    print(emp1.get_name())  # Output: Tom Nolan
  • hasattr(emp1, 'get_name'): This checks if the emp1 object has an attribute named 'get_name'. This could be any attribute (a method, a variable, etc.). It doesn't tell us if it's callable.
  • getattr(emp1, 'get_name'): This retrieves the attribute named 'get_name' from emp1.
  • callable(...): This is crucial. It checks if the retrieved attribute is callable (i.e., a function or method). This distinguishes a method from a simple data attribute.
  • The if statement only executes if both checks succeed, making sure that you won't get exceptions.

Why try/except AttributeError is Insufficient​

You might be tempted to use a try/except block to catch an AttributeError:

class Employee():
    def __init__(self, first, last):
        self.first = first
        self.last = last

    def get_name(self):
        return f'{self.first} {self.last}'

emp1 = Employee('Tom', 'Nolan')

try:
    result = emp1.get_name() # Call it directly
    print(result) # Output: Tom Nolan
except AttributeError:
    print('The attribute does NOT exist')
  • The problem with using the try/except block is that it will check for attribute, but it won't tell you if the attribute is a callable.

Using getattr to Check a Method and Call It​

You can use the getattr() method to get a method from an object, provide a default value, and execute it if the attribute is callable:

class Employee():
    
    def __init__(self, first, last):
        self.first = first
        self.last = last

    def get_name(self):
        return f'{self.first} {self.last}'

emp1 = Employee('Tom', 'Nolan')
method = getattr(emp1, 'get_name', None) # The method returns None
if callable(method):
    print(method()) # Output: Tom Nolan
  • The code will first attempt to get an attribute with a get_name and store it into method variable.
  • The second argument passed to getattr is the attribute name.
  • If the attribute does not exist, getattr will return the default value, which is None.
  • The callable method is used to check if the attribute is callable.

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