问无法安装PyRFC-2.0.4

EN

ERROR: Command errored out with exit status 1:
     command: 'c:\users\20035128\appdata\local\programs\python\python37\python.exe' -c 
              'import sys, setuptools, tokenize; sys.argv[0] = 
              '"'"'C:\\Users\\20035128\\AppData\\Local\\Temp\\pip-req-build-4ouyveyv\\setup.py'"'"'; 
              __file__='"'"'C:\\Users\\20035128\\AppData\\Local\\Temp\\pip-req-build-4ouy
              veyv\\setup.py'"'"';f=getattr(tokenize, '"'"'open'"'"', open (__file__);
              code=f.read().replace('"'"'\r\n'"'"',              '"'"'\n'"'"');f.close();
              exec(compile(code, __file__, '"'"'exec'"'"'))' egg_info --egg-base 
              'C:\Users\20035128\AppData\Local\Temp\pip-pip-egg-info-fwk_dg_0'
         cwd: C:\Users\20035128\AppData\Local\Temp\pip-req-build-4ouyveyv\
    Complete output (1 lines):
    Environment variable SAPNWRFC_HOME not set. Please specify this variable with the root 
              directory of the SAP NW RFC Library.
    ----------------------------------------
WARNING: Discarding file:///C:/Users/20035128/Downloads/PyRFC-2.0.4.tar.gz. Command errored 
              out with exit status 1: python setup.py egg_info Check the logs for full command output.  
ERROR: Command errored out with exit status 1: python setup.py egg_info Check the logs for 
              full command output.