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 using locks in multithreading in python3
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
       while i<=100:
           print(" I is now %d \n" %i)
    def f2(self):
        j = self.j
        global lock
        while j<=50:
            print("J is now %d \n" %j)
    def Main1(self):
        lock = threading.Lock()

if __name__ == '__main__':

Getting error in the code
Exception in thread Thread-2: Traceback (most recent call last): File "C:\Python37\lib\", line 917, in _bootstrap_inner File "C:\Python37\lib\", line 865, in run self._target(*self._args, **self._kwargs) File "D:\Python\PythonExamples\Multithreading\", line 23, in f2 lock.acquire() NameError: name 'lock' is not defined
Move line #28 somewhere outside the class definition, e.g. to the line #2. Global statements not necessary here.

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

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