Initialization of variable in python and C [duplicate]

Question

This question already has answers here:

What is the Python equivalent of static variables inside a function? (31 answers)

Closed 10 years ago.

I'm rewriting a C code to python but it seems I've stuck.

I have the function in C:

 double GetArrival()
 /* ---------------------------------------------
 * generate the next arrival time, with rate 1/2
 * ---------------------------------------------
 */ 
 {
 static double arrival = START;
 SelectStream(0); 
 arrival += Exponential(2.0);
 return (arrival);
 }

This function is called from a main() function. As you can see every time it is called, an exponential random rate of 2.0 is added to arrival. All you have to know is that it's a custom function that returns a random variable.

After consulting ddd on the C file which works as it should, I realized that in the following python "equivalent" the variable arrival gets initialized to START = 0 everytime the function GetArrival() is called. This for some reason doesn't happen in the C, except the first time the function is called.

def GetArrival():
 arrival = START
 SelectStream(0)
 arrival += Exponential(2.0)
 return arrival

So I thought I should omit this evil initialization and that should do it. Did not, because in that case I get the following error:

UnboundLocalError: local variable 'arrival' referenced before assignment

Which kinda makes sense.

So my question is how can I make the python code work like the one in C, without having the variable arrival initialize to zero every time?

Thanks.

Answer 1

This has to do with how python treats the static variable differently from C I think. Try referring to making a static variable in python (static var in function, not class). This stack overflow reference should be of help to you.

• Jon Lund Steffensen: This is caused by the static variable (en.wikipedia.org/wiki/Static_variable) not differences in "execution stack".
• user239546: Thanks @jonls. Updated accordingly.