(env3) [MrYang:Desktop]$ python3 -m pip install pycurl
Looking in indexes: http://mirrors.aliyun.com/pypi/simple/
Collecting pycurl
  Downloading http://mirrors.aliyun.com/pypi/packages/e8/e4/0dbb8735407189f00b33d84122b9be52c790c7c3b25286826f4e1bdb7bde/pycurl-7.43.0.2.tar.gz (214kB)
    100% |████████████████████████████████| 215kB 3.1MB/s
    Complete output from command python setup.py egg_info:
    Using curl-config (libcurl 7.43.0)
    Traceback (most recent call last):
      File "<string>", line 1, in <module>
      File "/private/var/folders/dx/m2t9qg010gg9pk5v8xzt4gxc0000gn/T/pip-install-bn546qog/pycurl/setup.py", line 913, in <module>
        ext = get_extension(sys.argv, split_extension_source=split_extension_source)
      File "/private/var/folders/dx/m2t9qg010gg9pk5v8xzt4gxc0000gn/T/pip-install-bn546qog/pycurl/setup.py", line 582, in get_extension
        ext_config = ExtensionConfiguration(argv)
      File "/private/var/folders/dx/m2t9qg010gg9pk5v8xzt4gxc0000gn/T/pip-install-bn546qog/pycurl/setup.py", line 99, in __init__
        self.configure()
      File "/private/var/folders/dx/m2t9qg010gg9pk5v8xzt4gxc0000gn/T/pip-install-bn546qog/pycurl/setup.py", line 316, in configure_unix
        specify the SSL backend manually.''')
    __main__.ConfigurationError: Curl is configured to use SSL, but we have not been able to determine which SSL backend it is using. Please see PycURL documentation for how to specify the SSL backend manually.

    ----------------------------------------
Command "python setup.py egg_info" failed with error code 1 in /private/var/folders/dx/m2t9qg010gg9pk5v8xzt4gxc0000gn/T/pip-install-bn546qog/pycurl/

The solution is as follows
# First upgrade PIP
Sudo Python-m PIP install — Upgrade — Force PIP
You can then specify the version number to install (the version number can be found in the error log)
Sudo PIP install pycurl = = 7.43.0