Impersonating a Static Variable in Python

# mimic a static variable to count how many times a function or method has been called
# (static comes from C, where a static variable in the function retains its last value)
# tested with Python24 by      vegaseat     29may2006

# using a global variable:
def static_num1() :
   global x
   x += 1
   return x

x = 0                # x increases with each call
print static_num1()  # 1
print static_num1()  # 2
print static_num1()  # 3
    
print "-"*30

# like a global variable but a little safer, use function.attribute:
def static_num2():
    static_num2.x += 1
    return static_num2.x

static_num2.x = 0    # at least you know the function x is used for
print static_num2()  # 1
print static_num1()  # 2
print static_num1()  # 3

print "-"*30

# use a mutable object like a list element as default argument:
def static_num3(list1=[0]):
    """The function's default is a list with one element = zero.
    Since the list is a mutable object it retains its address,
    as the function's default is created at compile time.
    Whatever you put into this list as element is retained too"""
    list1[0] += 1
    return list1[0]

print static_num3()  # 1
print static_num3()  # 2
print static_num3()  # 3

print "-"*30

# use a generator function (yield replaces return):
def static_num4():
    k = 0
    while True:
       k += 1
       yield k

static4 = static_num4().next  # next is needed with generator functions

print static4()  # 1  () is needed for call
print static4()  # 2
print static4()  # 3

print "-"*30

# use a class and classmethod():
class Static5:
    k = 0
    def count(self):
        self.k += 1
        return self.k
    # this allows you to simply call Static5.count()
    count = classmethod(count)
    
print Static5.count()  # 1
print Static5.count()  # 2
print Static5.count()  # 3

print "-"*30

# same idea with @decorator:
class Static6:
    k = 0
    # allows you to simply call Static6.count()
    @classmethod
    def count(self):
        self.k += 1
        return self.k

print Static6.count()  # 1
print Static6.count()  # 2
print Static6.count()  # 3

print "-"*30

# example of using the default list as a counter in a function:
def f1(str1, count=[0]):
    # your code
    str1 = str1 + " and butter"
    # the counter
    count[0] += 1
    # return a tuple
    return count[0], str1

print f1("bread")  # (1, 'bread and butter')
print f1("bread")  # (2, 'bread and butter')
print f1("bread")  # (3, 'bread and butter')

print "-"*30

# another example, you could make up all the lyrics from 99 on down:
def beer(count=[100]):
    # the counter
    count[0] -= 1
    # your code
    str1 = str(count[0]) + " bottles of beer on the wall ..."
    return str1

print beer()  # 99 bottles of beer on the wall ...
print beer()  # 98 bottles of beer on the wall ...
print beer()  # 97 bottles of beer on the wall ...