Using getattr() to access built-in functions

Question

I would like to use getattr() to access Python's built-in functions. Is that possible?

For example:

getattr(???, 'abs')

I know I can just simply do:

>>> abs
<built-in function abs>

But I want to use getattr, because the keyword names are strings.

Answer 1

The builtins module:

You could try importing builtins module:

>>> import builtins
>>> getattr(builtins, 'abs')
<built-in function abs>
>>> 

As mentioned in the documentation:

This module provides direct access to all ‘built-in’ identifiers of Python; for example, builtins.open is the full name for the built-in function open(). See Built-in Functions and Built-in Constants for documentation.

So the above mentions that builtins.open is the open function. So abs is the same builtins.abs is the same thing as abs. But for gettatr, getattr(builtins, 'abs') is also the same as builtins.abs.

The original __bultins__ (NOT RECOMMENDED):

You could try getting from the __builtins__:

>>> getattr(__builtins__, 'abs')
<built-in function abs>
>>> 

As mentioned in the documentation:

CPython implementation detail: Users should not touch __builtins__; it is strictly an implementation detail. Users wanting to override values in the builtins namespace should import the builtins module and modify its attributes appropriately.

The builtins namespace associated with the execution of a code block is actually found by looking up the name __builtins__ in its global namespace; this should be a dictionary or a module (in the latter case the module’s dictionary is used). By default, when in the main module, __builtins__ is the built-in module builtins; when in any other module, __builtins__ is an alias for the dictionary of the builtins module itself.

As you can see, it's not recommended, also usually the __builtins__ is a dict, rather than a module.

If you write your code in modules, __builtins__ would return dictionary aliases of the builtins module, which would give something like: {..., 'abs': <built-in function abs>, ...}.

More on getattr:

Just to have more idea about getattr, as mentioned in the documentation:

Return the value of the named attribute of object. name must be a string. If the string is the name of one of the object’s attributes, the result is the value of that attribute. For example, getattr(x, 'foobar') is equivalent to x.foobar. If the named attribute does not exist, default is returned if provided, otherwise AttributeError is raised.

So:

>>> import builtins
>>> getattr(builtins, 'abs')
<built-in function abs>
>>> 

Is the same as:

>>> import builtins
>>> builtins.abs
<built-in function abs>
>>> 

So you might be wondering since:

>>> abs
<built-in function abs>

Gives the same thing, why we can't just do:

getattr(abs)

The reason we can't do that is that that getattr is suppose to be calling methods/functions/classes of a classes/modules.

The reason using getattr(builtins, 'abs') works is because builtins is a module and abs is a class/method, it stores all the built-in Python keywords as methods in that module.

All the keywords are showed on this page of the documentation.