Python .join()

The .join() method delays a program’s flow of execution until the target thread has been completely read.

Syntax

thread_object.join(timeout)

The .join() method always returns None. There is also a timeout parameter that is set to None by default. If set otherwise, it must be represented in seconds with a floating-point value.

Example

The following example features two threads, thread_A and thread_B. Each thread makes a call to .start(), immediately followed by a call to .join().

import threading

def is_divisible(dividend, divisor):
  print("Starting...")
  if(dividend % divisor == 0):
    print(True)
  else:
    print(False)
  print("Finished")

thread_A = threading.Thread(target=is_divisible, args=(28, 14))
thread_B = threading.Thread(target=is_divisible, args=(34, 7))

thread_A.start()
thread_A.join()

thread_B.start()
thread_B.join()

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The output will look like this:

Starting...
True
Finished
Starting...
False
Finished

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The second thread, thread_B, cannot start before thread_A is finished due to .join().

Codebyte Example

In the example below, the .join() method allows the last print() statement to appear at the expected time in the program’s flow of execution:

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