Insert variable into global namespace from within a function?

Question

Is it possible to add an object to the global namespace, for example, by using globals() or dir()?

def insert_into_global_namespace(var_name, value):
    globals()[var_name] = value


insert_into_global_namespace('my_obj', 'an object')
print(f'my_obj = {my_obj}')

But this only works in the current module.

Asked By: Dan

||

Source

Answer 1

Yes, just use the global statement.

def func():
    global var
    var = "stuff"

Answered By: BrenBarn

Answer 2

But be aware that assigning function variables declared global only injects into the module namespace. You cannot use these variables globally after an import:

from that_module import call_that_function
call_that_function()
print(use_var_declared_global)

and you get

NameError: global name 'use_var_declared_global' is not defined

You would have to do import again to import also those new “module globals”.
The builtins module is “real global” though:

class global_injector:
    '''Inject into the *real global namespace*, i.e. "builtins" namespace or "__builtin__" for python2.
    Assigning to variables declared global in a function, injects them only into the module's global namespace.
    >>> Global= sys.modules['__builtin__'].__dict__
    >>> #would need 
    >>> Global['aname'] = 'avalue'
    >>> #With
    >>> Global = global_injector()
    >>> #one can do
    >>> Global.bname = 'bvalue'
    >>> #reading from it is simply
    >>> bname
    bvalue

    '''
    def __init__(self):
        try:
            self.__dict__['builtin'] = sys.modules['__builtin__'].__dict__
        except KeyError:
            self.__dict__['builtin'] = sys.modules['builtins'].__dict__
    def __setattr__(self,name,value):
        self.builtin[name] = value
Global = global_injector()

Answered By: Roland Puntaier

Answer 3

I don’t think anyone has explained how to create and set a global variable whose name is itself the value of a variable.

Here’s an answer I don’t like, but at least it works[1], usually[2].

I wish someone would show me a better way to do it. I have found several use cases and I’m actually using this ugly answer:

########################################
def insert_into_global_namespace(
    new_global_name,
    new_global_value = None,
):
    executable_string = """
global %s
%s = %r
""" % (
        new_global_name,
        new_global_name, new_global_value,
    )
    exec executable_string  ## suboptimal!

if __name__ == '__main__':
    ## create global variable foo with value 'bar':
    insert_into_global_namespace(
        'foo',
        'bar',
    )
    print globals()[ 'foo']
########################################

Python exec should be avoided for many reasons.
N.B.: Note the lack of an “in” keyword on the “exec” line (“unqualified exec”).

Answered By: Steve Newcomb

Answer 4

It is as simple as

globals()['var'] = "an object"

and/or

def insert_into_namespace(name, value, name_space=globals()):
    name_space[name] = value

insert_into_namespace("var", "an object")

Remark that globals is a built-in keyword, that is, 'globals' in __builtins__.__dict__ evaluates to True.

Answered By: jolvi

Answer 5

A more terse version of Roland Puntaier’s answer is:

import builtins

def insert_into_global_namespace():
    builtins.var = 'an object'

Answered By: 1''

Insert variable into global namespace from within a function?

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