Python - Thread Synchronization and Thread-safe Operations

This is the best article on thread synchronization in Python that I have come across: Thread Synchronization Mechanisms in Python

It is very clearly explained and just helped me solve a major concurrency issues I was having.

Especially interesting is the list of thread safe operations in Python.

Here are some thread-safe operations:

  • reading or replacing a single instance attribute
  • reading or replacing a single global variable
  • fetching an item from a list
  • modifying a list in place (e.g. adding an item using append)
  • fetching an item from a dictionary
  • modifying a dictionary in place (e.g. adding an item, or calling the clear method)

Here is an explanation of global value mutation that are thread safe:

http://effbot.org/pyfaq/what-kinds-of-global-value-mutation-are-thread-safe.htm

Update: Now I am confused. Doesn't this example in the article contradict bullet point 2 above?

Update Update: See comments below for better explanation and info.