Error when trying to get object type in python

Question

I have a main script, which imports another python library that I've been writing. The library contains the following command:

print getattr(__builtins__, "list")

This produces the following error when I call it from the library:

'dict' object has no attribute 'list'

But, if I copy and paste that same command into the main script it works fine. Any ideas why this isn't working?

The header of my main file looks like this:

#/usr/bin/env python
from sys import argv
import re, sys, os, argparse
sys.path.extend(map(os.path.abspath, ['C:/Users/xxxx/scripts/modules/']))
import general

The header for my "general" library is:

#!/usr/bin/env python
from sys import argv
import re, sys, os, argparse

def getBuiltin(name):
    ##Convert a string into an attribute
    try:
        return getattr(__builtins__, name)
    except Exception as e:
        print "Unhandled type in function \"get_builtin\""
        print name
        print e
        exit()

I was calling the library like this:

print general.getBuiltin("list")

where, "getBuiltin" is the name of my function

Please provide more context to your question, it would help seeing at least the header of your main script and the library you are referring to — Moe
– Moe, Commented Jul 12, 2017 at 14:39
Yes, you need to provide a minimal reproducible example so we can reproduce and diagnose. You wouldn’t expect your doctor could help much if you said, “It hurts when I do cartwheels.” She’d need to observe and run tests to diagnose. — Arya McCarthy
– Arya McCarthy, Commented Jul 12, 2017 at 14:58
can you dump type(__builtins__)? it should be a module, not a dict, so wondering if you have reassigned it somewhere. — Corley Brigman
– Corley Brigman, Commented Jul 12, 2017 at 14:59
Hi, yes, you're correct- when I print type(__builtins__) in the main script, it returns <type 'module'>, whereas in the library, it returns <type 'dict'>. — Conor
– Conor, Commented Jul 12, 2017 at 15:09

Alexandru Iulian Surdu · Accepted Answer · 2017-07-12 15:18:53Z

1

You can also check this question: Python: What's the difference between __builtin__ and __builtins__?

As you can see in akent answer, builtins is different in main module and another module:

Straight from the python documentation: http://docs.python.org/reference/executionmodel.html

By default, when in the main module, builtins is the built-in module builtin (note: no 's'); when in any other module, builtins is an alias for the dictionary of the builtin module itself.

builtins can be set to a user-created dictionary to create a weak form of restricted execution.

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 builtin (no 's') module and modify its attributes appropriately. The namespace for a module is automatically created the first time a module is imported. Note that in Python3, the module builtin has been renamed to builtins to avoid some of this confusion.

answered Jul 12, 2017 at 15:18

Alexandru Iulian Surdu

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1 Comment

Conor Over a year ago

Added import __builtin__ and change to getattr(__builtin__, "list"). Thanks for the help

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