The Murchison Widefield Array (MWA) is a low frequency telescope (80-300 MHz - same as TV and radio) in the Murchison region 800 km NE of Perth. It has been running full time since mid 2013, and has collected around 13 Pbytes of data so far. The MWA has no moving parts, making it a 'software only' telescope, and this talk will describe the software. Apart from the low-level data processing (two programs written in C/C++ and CUDA), almost all of the MWA software is in Python. In total there are hundreds of processes running on dozens of machines, ranging from hardware control via digital IO and I2C on embedded Linux machines through to user interface and status/diagnostics pages using Django.