Introduction

Threads allow applications to perform multiple tasks at once. Multi-threading is important in many applications, from primitive servers to today's complex and hardware-demanding games, so, naturally, many programming languages sport the ability to deal with threads. This includes Python.

However, Python's support for multi-threading is not without limitations and consequences, as Guido van Rossum writes:

"Unfortunately, for most mortals, thread programming is just Too Hard to get right.... Even in Python -- every time someone gets into serious thread programming, they send me tons of bug reports, and half of them are subtle bugs in the Python interpreter, half of them are subtle problems in their own understanding of the consequences of multiple threads...."

Before we begin to look at the code that makes threading work, the most important feature we must look at is Python's global interpreter lock. If two or more threads were to attempt to manipulate the same object at the same time, problems would inevitably pop up. The global interpreter lock fixes this. Only one thread can perform an action at any given time. Python automatically switches between threads when it is needed.