How to Get a Function Name as a String in Python?

Problem Formulation

Given a function object assigned to a name. How to get the name of the function as a string?

For example, consider the following function your_function. How to get the name "your_function" from this?

def your_function():
    pass

string_name = ???

Your desired value of the result stored in string_name is the string "your_function".

print(string_name)
# your_function

Method 1: Use the __name__ Attribute

The most Pythonic way to extract the name from any object or class is to use its __name__ attribute. Attributes enclosed in double underscores (dunder attributes) provide special functionality to Python programmers. For example, calling your_function.__name__ yields the string value 'your_function'.

def your_function():
    pass


string_name = your_function.__name__

print(string_name)
# your_function

However, there’s an important case where this method will fail.

๐Ÿ’ฃ ATTENTION: In Python, functions are objects. You can create multiple variables pointing to the same object in memory. Therefore, you could create two names func_1 and func_2 that both point to the same function object. When calling func_1.__name__ the result may be func_2 instead of func_1 what you expected.

This is showcased in the following minimal example:

def func_2():
    pass

func_1 = func_2
print(func_1.__name__)
# func_2

As both names point to the same memory object, but func_2 was pointing to it first, the name of the object is func_2. The memory usage of this code is visualized using the Python Tutor tool:

Both variables refer to the same function object that defaults as func_2 name.

Method 2: Use the __qualname__ attribute

To extract the name from any object or class, you can also use its __qualname__ attribute. For example, calling your_function.__qualname__ yields the string value 'your_function'. You’d use __qualname__ over __name__ if you’d also need some context such as the class defining the method.

The following code creates a function and a method inside a class. It then compares the output of the __name__ and __qualname__ attributes for both the function and the class:

def my_function():
    pass


class My_Class(object):
    def my_method(self):
        pass


print(my_function.__name__)             # "my_function"
print(My_Class.my_method.__name__)      # "my_method"

print(my_function.__qualname__)         # "my_function"
print(My_Class.my_method.__qualname__)  # "My_Class.my_method"

You can dive deeper into the idiosyncrasies of __qualname__ here and here.


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