How to check if a variable is a Function in Python

# Table of Contents

1. Check if a variable is a Function in Python
2. Check if a variable is a Function using inspect.isfunction()
3. Check if a variable is a Function using types.FunctionType
4. Check if a variable is a Function using hasattr()

# Check if a variable is a Function in Python

Use the callable() function to check if a variable is a function, e.g. if callable(function):.

The callable() function takes an object and returns True if the object is callable, otherwise, False is returned.

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def do_math(a, b):
    return a + b


print(callable(do_math))  # 👉️ True
print(callable('hello'))  # 👉️ False

if callable(do_math):
    # 👇️ this runs
    print('The variable is a function')
else:
    print('The variable is NOT a function')

We used the callable() built-in function to check if a variable is a function.

The callable function takes an object as an argument and returns True if the object appears callable, otherwise False is returned.

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print(callable(lambda x: x * 2))  # 👉️ True
print(callable(3.14))  # 👉️ False

If the callable() function returns True, it is still possible that calling the object fails, however, if it returns False, calling the object will never succeed.

It also returns True for classes.

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class Employee:
    pass


print(callable(Employee))  # 👉️ True
print(callable(int))  # 👉️ True

# Check if a variable is a Function using inspect.isfunction()

An alternative approach is to use the inspect.isfunction() method.

The inspect.isfunction() method returns True if the supplied object is a Python function, otherwise False is returned.

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import inspect


def do_math(a, b):
    return a + b


print(inspect.isfunction(do_math))  # 👉️ True

if inspect.isfunction(do_math):
    # 👇️ this runs
    print('The variable is a function')
else:
    print('The variable is NOT a function')

The inspect.isfunction() method takes an object and returns True if the object is a Python function.

The method would return False if passed another callable, e.g. a class.

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import inspect

class Employee:
    pass


print(inspect.isfunction(Employee))  # 👉️ False
print(inspect.isfunction(int))  # 👉️ False

The method returns False for most built-in functions because they are implemented in C, not in Python.

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import inspect

print(inspect.isfunction(zip))  # 👉️ False
print(inspect.isfunction(map))  # 👉️ False

print(callable(zip))  # 👉️ True
print(callable(map))  # 👉️ True

The zip and map functions are implemented in C, so the inspect.isfunction() method returned False.

# Check if a variable is a Function using types.FunctionType

You might also use the types.FunctionType class to check if a variable is a function.

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import types

def do_math(a, b):
    return a + b

print(isinstance(do_math, types.FunctionType))  # 👉️ True

print(isinstance(zip, types.FunctionType))  # 👉️ False
print(isinstance(map, types.FunctionType))  # 👉️ False

However, the class also returns True only for Python functions.

The isinstance() function returns True if the passed-in object is an instance or a subclass of the passed-in class.

The types.FunctionType class works in the same way the inspect.isfunction() method does.

However, the class is a bit more indirect, so there's no good reason to use it.

# Check if a variable is a Function using hasattr()

You can also use the hasattr() function to check if a variable is a function.

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def do_math(a, b):
    return a + b


if hasattr(do_math, '__call__'):
    # 👇️ this runs
    print('The variable is a function')
else:
    print('The variable is NOT a function')

print(hasattr(do_math, '__call__'))  # 👉️ True
print(hasattr('bobbyhadz.com', '__call__'))  # 👉️ False

The hasattr() function takes the following 2 parameters:

The hasattr() function returns True if the string is the name of one of the object's attributes, otherwise False is returned.

If the object has a __call__ attribute then it is callable.

# Additional Resources

You can learn more about the related topics by checking out the following tutorials:

• Call a Function by a String name in Python
• How to call a Function N times in Python
• Run a Function or a Loop only Once in Python
• How to Print the output of a Function in Python
• Why does my function print None in Python [Solved]
• TypeError: Object of type function is not JSON serializable
• TypeError: 'function' object is not subscriptable in Python
• SyntaxError: cannot assign to function call here in Python
• How to use a Variable from another Function in Python
• How to use Function Pointers in Python
• Python: Declaring a Variable without assigning it a Value