Make all variables in a Python function global

Question

Is there a simple way to make all variables in a function global?

I have 20 odd variables in a function and naming them global one by one doesn't make nice code... to me anyway :)

Solution 1

Warning: Don't try this at home, you might burn it down.

There is no legitimate reason to do the following in the course of normal day-to-day programming. Please review the other answers to this question for more realistic alternatives.

I can barely imagine why you would want to do this, but here is a way to do it:

def f(a, b, c):
    d = 123
    e = 'crazy, but possible'
    globals().update(locals())

def g():
    print a, b, c, d ,e

>>> globals()
{'g': <function g at 0x875230>, 'f': <function f at 0x8751b8>, '__builtins__': <module '__builtin__' (built-in)>, '__package__': None, '__name__': '__main__', '__doc__': None}

>>> g()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<stdin>", line 2, in g
NameError: global name 'a' is not defined

>>> f(10, 20, 'blah')
>>> g()
10 20 blah 123 crazy, but possible

>>> globals()
{'a': 10, 'c': 'blah', 'b': 20, 'e': 'crazy, but possible', 'd': 123, 'g': <function g at 0x875230>, 'f': <function f at 0x8751b8>, '__builtins__': <module '__builtin__' (built-in)>, '__package__': None, '__name__': '__main__', '__doc__': None}

Solution 2

The pythonic way to do this is either to keep the variables in local scope (i.e. define them within each function) and pass them between the functions as arguments / return values; or to keep your variables as attributes of an object or class making your "functions" methods in that class. Either way is OK, but the global keyword is designed specifically to put you off using it in the way you describe. Global variables are not just "bad style" but they make your code very difficult to maintain, as any invariants that your variables need to stick to need to be checked in every function.

Here is an example of good style (with functions):

def quads(a, b, c):
    x1 = (-1.0 * b + math.sqrt(b * b - 4.0 * a * c)) / (2.0 * a)
    x2 = (-1.0 * b - math.sqrt(b * b - 4.0 * a * c)) / (2.0 * a)
    return x1, x2

def pretty(a, b, c, x1, x2):
    eqn = "%fx^2 + %fx + %c" % (a, b, c)
    print "The first solution to the equation %s is: %f" % (eqn, x1)
    print "The second solution to the equation %s is: %f" % (eqn, x2)
    return

def main():
    a = 100
    b = 200
    c = 300
    x1, x2 = quads(a, b, c)
    pretty(a, b, c, x1, x2)
    return

if __name__ == '__main__':
    main()

Here is an example of good style (with OOP):

class Quadratic(object):

    def __init__(self, a, b, c):
        self.a = a
        self.b = b
        self.c = c
        self.x1 = None 
        self.x2 = None 
        self.solve() # Set x1 and x2 to correct values
        # To maintain the invariant between a, b, c and x1, x1
        # we should override __setattr__ or use descriptors or
        # properties so that self.solve() is called every time
        # a, b, or c are updated.
        return

    def solve(self):
        self.x1 = (-1.0 * self.b +
                   math.sqrt(self.b * self.b - 4.0 * self.a * self.c)) / (2.0 * self.a)
        self.x2 = (-1.0 * self.b - 
                   math.sqrt(self.b * self.b - 4.0 * self.a * self.c)) / 2.0 * self.a
        return 

    def pretty(self):
        eqn = "%fx^2 + %fx + %c" % (self.a, self.b, self.c)
        print "The first solution to the equation %s is: %f" % (eqn, self.x1)
        print "The second solution to the equation %s is: %f" % (eqn, self.x2)
        return

def main():
    quad = Quadratic(100, 200, 300)
    quad.pretty()
    return

if __name__ == '__main__':
    main()

Solution 3

There's no way to declare them all as global, and you really don't want to. Those 20 variables probably should be turned into an object with 20 attributes instead.

Solution 4

The simplest solution is to have only a single global — or, better yet, to figure out how to pass it in to the function. Using it as a global would look like this (again, I am showing the simplest possible case, not necessarily the best use of Python):

class Info(object):  # or whatever you want to name the container
    """Holder for global information."""

info = Info()        # single instance we will use

def my_function():
    print "Here is some info:"
    print info.a, info.b, info.c

info.a = 3
info.b = 8
info.c = []

if __name__ == '__main__':
    my_function()

Again, I would probably pass info to the function instead. But since your question was about a global, it's shown here as a global.

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