Can you tell me which specific version of python you are using. If you can not then go to your command promp and run the command:
The main problem with your error must be Python command is not installed or listed on your path environment variable.
Please check your python path environment variable directory.
Check is there any file named :
Try to execute the python file from the default installation directory.
If it is not working then uninstall and reinstall python 64 bit for windows.
And please make sure that in your directory the python path variable is not more than one.
And please reopen atom editor after you reset your path.