Get built-in function from the function name

Question

How can I get the int(), float(), dict(), etc. callables from their names? For example, I'm trying to save Python values to xml and storing the variable type as a string. Is there a way to get the callable from the string when converting from string back to the Python type?

Normally I would do something like getattr(myobj, 'str'), but there is no module to use as the first argument for these built-in conversion functions. I've also tried getattr(object, 'str'), but this doesn't work either since these functions are not part of the base 'object' type, merely globals to the language.

Sven Marnach · Accepted Answer · 2012-03-01 19:28:52Z

20

Normally I would do something like getattr(myobj, 'str'), but there is no module to use as the first argument for these built-in conversion functions.

Wrong, there is:

import __builtin__
my_str = getattr(__builtin__, "str")

(In Python 3.x: import builtins)

answered Mar 1, 2012 at 19:28

Sven Marnach

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durden2.0 Over a year ago

ah ha! Works like a charm. I was trying to use the builtins on object and other types, didn't know there was a module for it.

John La Rooy · Accepted Answer · 2012-03-01 19:38:01Z

6

You don't need to import anything

vars(__builtins__)['dict']
vars(__builtins__)['float']
vars(__builtins__)['int']

etc.

answered Mar 1, 2012 at 19:38

John La Rooy

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4 Comments

durden2.0 Over a year ago

I like this solution too. Would there be any reasons to use this vs. the above builtin module other than removing the import?

Sven Marnach Over a year ago

@durden2.0: This is a CPython implementation detail that shouldn't be relied upon. Better to import __builtin__. __builtins__ is sometimes a module and sometimes a dictionary. The code above will only work in the main module, not in other modules.

durden2.0 Over a year ago

@SvenMarnach oh good to know. Thanks! Are there other variables like builtins that can be a module or dictionary depending on the implementation? I'd like to have the ability to move to pypy or something similar in the future.

Sven Marnach Over a year ago

@durden2.0: __builtins__ might not even exist in other Python implementations. And within CPython, its type is inconsistent: __main__.__builtins__ is a module, while e.g. os.__builtins__ is a dict. There are only a few differences between PyPy and CPython. The most common show-stopper is that you are using some external module that is not supported by PyPy, e.g. NumPy or PyGTK. If in doubt, read the documentation of Python (the language), PyPy and the libraries you are using.

Praveen Gollakota · Accepted Answer · 2012-03-01 19:30:07Z

0

One quick way is to invoke it from the __builtin__ module. For example

>>> import __builtin__
>>> __builtin__.__dict__['str'](10)
'10'

answered Mar 1, 2012 at 19:30

Praveen Gollakota

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