python3: is there a kind of static variable in Python?

Question

I'm newbie in python.

Is there analogue of static keyword in python? I needed to implement a simple function allocating an integer ID from the pool, in fact it just increments a global variable and returns it:

id = -1
def generate_id():
 global id
 id += 1
 return id

Is this the right way to do it? In C I could declare a static variable in the function.

• FObersteiner: Does this answer your question? What is the Python equivalent of static variables inside a function?
• Mark: @MrFuppes, thanks, I will read that thread.

Answer 1

The simple way would be to return a "generator" function that forms a closure over a local, then just manipulate the local:

def new_id_generator():
 id = 0
 def gen():
 nonlocal id
 id += 1
 return id
 return gen
g = new_id_generator()
print(g(), g()) # 1 2

• Mark: thanks for feedback. In new_id_generator() function -- is it guaranteed that id variable is only visible inside of new_id_generator() ? So in other words, any other code in the script won't be able to touch/change id ?
• Carcigenicate: @Mark There's potentially some bizarre hack by inspecting stack frames that will allow it to be changed, but it will be much harder than it would by having it as a attribute of a function or your own class. Python doesn't have strict "private" controls, so you can really only discourage certain behavior, not outright prevent it. I think this is about as "private" as you'll be able to get.

Answer 2

In python there is no such thing as "static" keyword unlike java.

For Funtions

You can add attributes to a function, and use it as a static variable.

def incrfunc():
 incrfunc.tab += 1
 print incrfunc.tab
# initialize
incrfunc.tab = 0

For Class

However, if you are making use of the classes in python below is the language convention.

All variables which are assigned a value in class declaration are class variables. And variables which are assigned values inside class methods are instance variables.

class CSStudent: 
 stream = 'cse' # Class Variable 
 def __init__(self,name,roll): 
 self.name = name # Instance Variable 
 self.roll = roll # Instance Variable 

NOTE: If you ask me, it would always be good to make use of classes and use them inside off a class, it is my opinion.