Functionality like local static in C

[Mirko]

Am 14.04.2022 um 17:02 schrieb Cecil Westerhof via Python-list:
> In C when you declare a variable static in a function, the variable
> retains its value between function calls.
> The first time the function is called it has the default value (0 for
> an int).
> But when the function changes the value in a call (for example to 43),
> the next time the function is called the variable does not have the
> default value, but the value it had when the function returned.
> Does python has something like that?
> 

There are several ways to emulate that:


### With a mutable default argument

In [1]: def func(var=[-1]):
   ...:     var[0] += 1
   ...:     return var[0]
   ...:

In [2]: func()
Out[2]: 0

In [3]: func()
Out[3]: 1

In [4]: func()
Out[4]: 2


### with a callable class

In [12]: class Func():
    ...:     def __init__(self, var=-1):
    ...:         self.var = var
    ...:
    ...:     def __call__(self):
    ...:         self.var += 1
    ...:         return self.var
    ...:

In [13]: func = Func()

In [14]: func()
Out[14]: 0

In [15]: func()
Out[15]: 1

In [16]: func()
Out[16]: 2


### with a closure

In [29]: def outer(var=-1):
    ...:     def inner():
    ...:         nonlocal var
    ...:         var += 1
    ...:         return var
    ...:     return inner
    ...:

In [30]: func = outer()

In [31]: func()
Out[31]: 0

In [32]: func()
Out[32]: 1

In [33]: func()
Out[33]: 2


### with a generator

In [2]: def func(init=0, end=3):
   ...:     for var in range(init, end):
   ...:         yield var
   ...:

In [3]: for i in func():
   ...:     print(i)
   ...:
0
1
2


HTH