calling method within class in python

Question

I am trying to call method within a class; that call is the last line below, self.z()

class Wait:
 def __init__(self,a):
 self.a = a
 def countdown(self,a):
 for remaining in range(self.a, 0, -1):
 sys.stdout.write("\r")
 sys.stdout.write("{:2d} seconds remaining.".format(remaining))
 sys.stdout.flush()
 time.sleep(1)
 sys.stdout.write("\rWait Complete! \n")
 def z(self):
 self.countdown(100)
 self.z()

However, I get this error:

Traceback (most recent call last):
 File "./countdown.py", line 6, in <module>
 class Wait:
 File "./countdown.py", line 18, in Wait
 self.z()
NameError: name 'self' is not defined

How can I call countdown from another method within this class ?

• castis: Are you wanting to fire self.z() immediately upon object creation?
• Jean-François Fabre: self.z() that works only from within an instance method of the class. what do you want to achieve?
• Kevin: Does this really need to be a class at all? What's wrong with having countdown as a standalone function?
• Prakash R: There is already bunch of code where a class already exists, say class ABC. Other methods in this class ABC currently uses time.sleep where I have to, at times, wait for 100 seconds. Instead of using time.sleep I want to use method countdown which can be used by other methods in this class ABC. I do not want to create a separate class for just countdown. To summarize, how do I make use of method countdown within a class for other methods?
• Kevin: You call self.countdown(some_number), exactly as you have done. There's nothing wrong with countdown in your code; the problem is that you're calling z() in a place where you're not allowed to. Presumably in your real code, this won't be a problem.

Answer 1

The problem is that self is not defined in the class body; self is a parameter of each of the methods, but you're not inside any method at that point. I think you might be trying to test this with a 100-second countdown, which means that you need that bottom code in your main program:

class Wait:
 def __init__(self,a):
 self.a = a
 def countdown(self,a):
 for remaining in range(self.a, 0, -1):
 sys.stdout.write("\r")
 sys.stdout.write("{0:2d} seconds remaining.".format(remaining))
 sys.stdout.flush()
 time.sleep(1)
 sys.stdout.write("\rWait Complete! \n")
 def z(self):
 self.countdown(100)
ticker = Wait(10)
ticker.z()

Note that your code ignores the 100 value sent in from z, instead using the timer value set at creation. Also note that I've corrected your formatted output statement.

Can you take it from here?

• Prakash R: Not exactly what I wanted. As mentioned earlier, I just do not want to use another class for countdown/wait. I want to use countdown method in the same class what I have currently say class ABC so that I can use it within other methods of class ABC. Let's say, def z wants to execute a cli "abcd" and wants to wait for 100 sec.
• Prune: Then please clarify your question, perhaps showing a failed attempt with class ABC. Your posting gives all of the methods as being within Wait, and my answer preserves that. Your error is in placing active code in the body of a Class, and in trying to use a variable that's not defined at that level.
• Prune: Also, note that I did answer your given question: your countdown method is, indeed, callable from within the class. Your call of z is illegal, but having z invoke countdown is already correct.
• Prakash R: I apologize, my bad for not being clear. Let's say, I have same set of code as you have mentioned above, instead, the name of the class is class ABC. Now, I have 2 methods here countdown and z. No change in the code of countdown. The code for method z is as follows: def z(self): print("before execution of cli") self.countdown(100) print("Now executing cli abcd")
• Prune: What about it? All you've done here is to change the name of the class and add two print statements to z. This does not affect the answer I gave: z can easily call countdown, and any object of ABC can invoke its z method.