From the R Language Reference:

Packages which have a namespace have a different search path. When a search for an R object is started from an object in such a package, the package itself is searched first, then its imports, then the base namespace and finally the global environment and the rest of the regular search path. The effect is that references to other objects in the same package will be resolved to the package, and objects cannot be masked by objects of the same name in the global environment or in other packages.

It’s a little surprising that a package can look in your global environment. For example:

> library("findx")
> findx
function ()
x
<environment: namespace:findx>
> findx()
Error in findx() : object 'x' not found
> x = 100
> findx()
[1] 100

Writing code that looks up variables in the global namespace seems like a very bad idea. Basically this shows that it’s possible to shoot yourself in the foot if you try hard enough.

Python won’t let you:

In [1]: from findx import findx

In [2]: findx()
---------------------------------------------------------------------------
NameError                                 Traceback (most recent call last)
<ipython-input-2-177571e7b710> in <module>()
----> 1 findx()

/home/clark/junkyard/findx.py in findx()
      1 def findx():
----> 2     return x

NameError: name 'x' is not defined

In [3]: x = 100

In [4]: findx()
---------------------------------------------------------------------------
NameError                                 Traceback (most recent call last)
<ipython-input-4-177571e7b710> in <module>()
----> 1 findx()

/home/clark/junkyard/findx.py in findx()
      1 def findx():
----> 2     return x

NameError: name 'x' is not defined