using locks in multithreading in python3

[srm]

import threading
 
 
class Class1(threading.Thread):
    def __init__(self, i, j):
        self.i = i
        self.j = j
 
    def f1(self):
       i = self.i
       global lock
       lock.acquire()
       while i<=100:
           print(" I is now %d \n" %i)
           i=i+1
           lock.release()
        
    def f2(self):
        j = self.j
        global lock
        lock.acquire()
        while j<=50:
            print("J is now %d \n" %j)
            j=j+1
            lock.release()
         
    def Main1(self):
        lock = threading.Lock()
        t1=threading.Thread(target=self.f1)
        t2=threading.Thread(target=self.f2)


        t1.start()
        t2.start()
 
 
if __name__ == '__main__':
    ob=Class1(1,1)
    ob.Main1()

Getting error in the code

Error:
Exception in thread Thread-2:
Traceback (most recent call last):
  File "C:\Python37\lib\threading.py", line 917, in _bootstrap_inner
    self.run()
  File "C:\Python37\lib\threading.py", line 865, in run
    self._target(*self._args, **self._kwargs)
  File "D:\Python\PythonExamples\Multithreading\SyncThreadingPython.py", line 23, in f2
    lock.acquire()
NameError: name 'lock' is not defined

[scidam]

Move line #28 somewhere outside the class definition, e.g. to the line #2. Global statements not necessary here.

[noisefloor]

Hi,

couple of remarks on the code:

• Don't use global. In 99% of all cases it's a clear indication that the design pattern of your code is not good. global can be avoided in most cases.
  
• In case you need a lock within your class, make it an attribute of you class.
  
• The lock doesn't make sense here anyway at all, as there is no concurrent operation on anything.
  
• Your are using a very old school way of string formating... Use the string's format() method or for Python >= 3.6 f-strings.
  

Regards, noisefloor