Step 1 : Open Command prompt.
Step 2 : Browse to Scripts directory under Python 3.x installation folder (Skip this step if you have set the environment variables properly for Python 3.x).
Step 3 : Run following command, "python3 -m pip install -U mypy"
Step 4 : If you need the latest version then go on and install from git, "python3 -m pip install -U git+git://github.com/python/mypy.git"
Step 5 : Check the working of mypy by typing following command, "mypy PROGRAM_NAME"