How do I call setattr() on the current module?

Question

What do I pass as the first parameter “object” to the function setattr(object, name, value), to set variables on the current module?

For example:

setattr(object, "SOME_CONSTANT", 42);

giving the same effect as:

SOME_CONSTANT = 42

within the module containing these lines (with the correct object).

I’m generate several values at the module level dynamically, and as I can’t define __getattr__ at the module level, this is my fallback.

Asked By: Matt Joiner

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Source

Answer 1

import sys

thismodule = sys.modules[__name__]

setattr(thismodule, name, value)

or, without using setattr (which breaks the letter of the question but satisfies the same practical purposes;-):

globals()[name] = value

Note: at module scope, the latter is equivalent to:

vars()[name] = value

which is a bit more concise, but doesn’t work from within a function (vars() gives the variables of the scope it’s called at: the module’s variables when called at global scope, and then it’s OK to use it R/W, but the function’s variables when called in a function, and then it must be treated as R/O — the Python online docs can be a bit confusing about this specific distinction).

Answered By: Alex Martelli

Answer 2

You wouldn’t. You would do globals()["SOME_CONSTANT"] = 42
You wouldn’t. You would store dynamically-generated content somewhere other than a module.

Answered By: Mike Graham

Answer 3

If you must set module scoped variables from within the module, what’s wrong with global?

# my_module.py

def define_module_scoped_variables():
    global a, b, c
    a, b, c = 'a', ['b'], 3

thus:

>>> import my_module
>>> my_module.define_module_scoped_variables()
>>> a
NameError: name 'a' is not defined
>>> my_module.a
'a'
>>> my_module.b
['b']

Answered By: msw

Answer 4

In Python 3.7, you will be able to use __getattr__ at the module level (related answer).

Per PEP 562:

def __getattr__(name):
    if name == "SOME_CONSTANT":
        return 42
    raise AttributeError(f"module {__name__} has no attribute {name}")

Answered By: Trey Hunner

How do I call setattr() on the current module?

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