Static Variables in Python?

[Carsten Haese]

On Mon, 2006-07-31 at 15:21, Michael Yanowitz wrote:
>   Is it possible to have a static variable in Python - 
> a local variable in a function that retains its value.
> 
>  For example, suppose I have:
> 
> def set_bit (bit_index, bit_value):
>    static bits = [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]
>    bits [bit_index] = bit_value
> 
>    print "\tBit Array:"
>    int i
>    while (i < len(bits):
>       print bits[i],
>    print '\n'
> 
>  
>    I realize this can be implemented by making bits global, but can
> this be done by making it private only internal to set_bit()?  I don't
> want bits to be reinitialized each time. It must retain the set values
> for the next time it is called.

Python does not have static variables in the sense that C does. You can
fake it in various ways, though. If I had to do it, I'd define a
callable object instead of a function, along the lines of this:

class BitSetter(object):
  def __init__(self):
    self.bits = [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]
  def __call__(self, bit_index, bit_value):
    self.bits[bit_index] = bit_value
    # do something with self.bits here...
    print self.bits

set_bit = BitSetter()

Now you can call set_bit(...) as if it were a function, and it'll behave
the way you want.

Hope this helps,

Carsten.