Conditionally modify global variable

Question

I'd like to do something like this, but I get a SyntaxWarning and it doesn't work as expected

RAWR = "hi"
def test(bool):
    if bool:
        RAWR = "hello"   # make RAWR a new variable, don't reference global in this function
    else:
        global RAWR
        RAWR = "rawr"    # reference global variable in this function
    print RAWR           # if bool, use local, else use global (and modify global)

How do I get this to work? Passing in True or False modifies the global variable.

Answer 1

You cannot. Within a scope, a specific name refers either to a local variable, or to a non-local (eg global, or from an outer function) variable. Not both. The global RAWR line makes RAWR a global for the entire scope (that's why you get a warning, it doesn't do what you think it does), just like assignment to a variable makes it local for the entire scope. Edit: Thanks to veredesmarald, we now know it is in fact a syntax error in Python 2. This half of my answer only applies to Python 3 apparently.

You should just use a differently-named local variable, and in the branch where you want to "promote" it to a global, set the global and the local variable. (Or just don't use globals at all.)

Answer 2

The only easy way you can go would be

RAWR = "hi"
def test(newone):
    if newone:
        lR = "hello"   # make RAWR a new variable, don't reference global in this function
    else:
        global RAWR
        lR = RAWR      # reference global variable in this function
    print lR           # if bool, use local, else use global (and modify global)
    # modify lR and then
    if not newone:
        RAWR = lR

Another way, however, could be to abuse the concept of classes and objects to your purposes.

class store_RAWR(object):
    RAWR = "hi"
    def __init__(self, new): self.RAWR = new

def test(newone):
    if newone:
        myR = store_RAWR("hello") # get a (temporary) object with a different string
    else:
        myR = store_RAWR # set the class, which is global.
    # now modify myR.RAWR as you need

But this requires other program parts which use the global name to be changed as well.