Is the += operator thread-safe in Python?

I want to create a non-thread-safe chunk of code for experimentation, and those are the functions that 2 threads are going to call.

c = 0

def increment():
  c += 1

def decrement():
  c -= 1

Is this code thread safe?

If not, may I understand why it is not thread safe, and what kind of statements usually lead to non-thread-safe operations.

If it is thread-safe, how can I make it explicitly non-thread-safe?