os.environ['CUDA_LAUNCH_BLOCKING'] = '1'

This line of code sets the environment variable 'CUDA_LAUNCH_BLOCKING' to the value '1'.

In the context of machine learning and deep learning, this environment variable is used to control the behavior of CUDA kernels. When set to '1', it forces CUDA kernels to run synchronously, which means that the CPU will wait for the GPU to finish executing a kernel before proceeding to the next one. This can be useful for debugging and profiling, as it ensures that all CUDA operations are complete before moving on to the next step. However, it can also slow down training and inference times, as it limits the ability to overlap GPU and CPU computation.