Today I learned about the built-in function vars in Python.

Example usage of `vars` in the Python REPL.


Python has a bunch of built-in functions. Like, a lot! It's very difficult to keep track of all of them, remember them, and use them correctly.

A built-in function I just learned about is vars. I heard about it from Reuven Lerner (a Python trainer) in his newsletter “Better Developers”. (Disclaimer: that's a referral link, but I am a subscriber and avid reader of the newsletter, so it is a very honest recommendation!)

Looking at the Python documentation, we can see what vars does:

“Return the __dict__ attribute for a module, class, instance, or any other object with a __dict__ attribute.”

The documentation also goes on to say that “without an argument, vars() acts like locals().”. So that's not useful because we can always use locals().

When vars really shines is when you give it an argument, like a module or a class instance!

>>> class Person:
...     def __init__(self, name):
... = name
>>> p = Person("me")
>>> vars(p)
{'name': 'me'}

So, we can see that vars is a very handy way of inspecting an instance of a class you defined. Quite cool, right?

For things like built-in classes, or modules, vars is similar to dir. Recall that dir lists the names of all the attributes of an object, but vars will give you a mapping with the names of the attributes and the corresponding values:

>>> import math
>>> dir(math)
['__doc__', '__loader__', '__name__', '__package__', '__spec__', 'acos', 'acosh', 'asin', 'asinh', 'atan', 'atan2', 'atanh', 'ceil', 'comb', 'copysign', 'cos', 'cosh', 'degrees', 'dist', 'e', 'erf', 'erfc', 'exp', 'expm1', 'fabs', 'factorial', 'floor', 'fmod', 'frexp', 'fsum', 'gamma', 'gcd', 'hypot', 'inf', 'isclose', 'isfinite', 'isinf', 'isnan', 'isqrt', 'lcm', 'ldexp', 'lgamma', 'log', 'log10', 'log1p', 'log2', 'modf', 'nan', 'nextafter', 'perm', 'pi', 'pow', 'prod', 'radians', 'remainder', 'sin', 'sinh', 'sqrt', 'tan', 'tanh', 'tau', 'trunc', 'ulp']
>>> vars(math)
{'__name__': 'math', '__doc__': 'This module provides access to the mathematical functions\ndefined by the C standard.', ...}

That's it for now! Stay tuned and I'll see you around!

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