Calling dir() in Python

Question

What object is being queried when I call dir() in Python's interpreter?

I'm playing with a package that I want to be able to get the names for functions from the global dictionary. I thought that it would be dir(__global) but that wasn't it, nor was dir(sys.modules).

If I type dir() into a fresh interpreter session it says

['__builtins__', '__doc__', '__name__', '__package__']

What would be the ob in dir(ob) that would give me this same response?

Answer 1

Re-reading your question 8 years later, I now wonder if you are asking about dir() run interactively at the Python prompt, a situation which I and the other answers entirely failed to address.

In that case the actual answer is:

When you type dir() in the Python interpreter, it runs dir() on the __main__ module because that is the namespace in which the Python prompt runs the statements that you type.

To perform this operation yourself, simply run:

import sys
dir(sys.modules['__main__'])

You will see exactly the same names listed as when you run dir() interactively. Try making an assignment like a = 1 then run both plain dir() and also the expression shown above; you will see that they both show the same list of names that now includes 'a'.

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The dir() method invokes complex and deep operations to try to predict which attributes might exist on the object you query — but runs under the handicap that it cannot actually try to access the attribute names it finds to see if they would return AttributeError or not. I know, this answer is way more detail than you want right now; but for those who might stumble on this question later with more complicated needs, "Implementing __dir__ (and finding bugs in Pythons)" is a blog post by Michael Food detailing some of the magic.

Answer 2

dir() returns names in the current scope. I can't remember now if it's exactly equivalent to locals().keys(), or are there any differences.