Pip Install Twisted Error 1

在Mac osx 10.9.4的虚拟环境中使用pip install Twisted时，我得到了以下结果：

Command \"python setup.py egg_info\" failed with error code 1 in /private/var/folders/9r/3b500gbs3093ms87mqqbckr80000gn/T/pip-build-doynftp7/twisted/

我不确定如何解决。我使用了easy_install，但遇到了SSL验证问题。有人有相似的问题吗？以下是其余的错误消息。

 Collecting twisted
 Using cached Twisted-16.6.0.tar.bz2
 Complete output from command python setup.py egg_info:
Download error on https://pypi.python.org/simple/incremental/: [SSL: CERTIFICATE_VERIFY_FAILED] certificate verify failed (_ssl.c:749) -- Some packages may not be found!
Couldn't find index page for 'incremental' (maybe misspelled?)
Download error on https://pypi.python.org/simple/: [SSL: CERTIFICATE_VERIFY_FAILED] certificate verify failed (_ssl.c:749) -- Some packages may not be found!
No local packages or working download links found for incremental>=16.10.1
Traceback (most recent call last):
  File "", line 1, in 
  File "/private/var/folders/9r/3b500gbs3093ms87mqqbckr80000gn/T/pip-build-lqvxc68n/twisted/setup.py", line 21, in 
    setuptools.setup(**_setup["getSetupArgs"]())
  File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/distutils/core.py", line 108, in setup
    _setup_distribution = dist = klass(attrs)
  File "/Users/Complex-Cauchy/1/lib/python3.6/site-packages/setuptools/dist.py", line 317, in __init__
    self.fetch_build_eggs(attrs['setup_requires'])
  File "/Users/Complex-Cauchy/1/lib/python3.6/site-packages/setuptools/dist.py", line 372, in fetch_build_eggs
    replace_conflicting=True,
  File "/Users/Complex-Cauchy/1/lib/python3.6/site-packages/pkg_resources/__init__.py", line 851, in resolve
    dist = best[req.key] = env.best_match(req, ws, installer)
  File "/Users/Complex-Cauchy/1/lib/python3.6/site-packages/pkg_resources/__init__.py", line 1123, in best_match
    return self.obtain(req, installer)
  File "/Users/Complex-Cauchy/1/lib/python3.6/site-packages/pkg_resources/__init__.py", line 1135, in obtain
    return installer(requirement)
  File "/Users/Complex-Cauchy/1/lib/python3.6/site-packages/setuptools/dist.py", line 440, in fetch_build_egg
    return cmd.easy_install(req)
  File "/Users/Complex-Cauchy/1/lib/python3.6/site-packages/setuptools/command/easy_install.py", line 668, in easy_install
    raise DistutilsError(msg)
distutils.errors.DistutilsError: Could not find suitable distribution for Requirement.parse('incremental>=16.10.1')
 ----------------------------------------

Command \"python setup.py egg_info\" failed with error code 1 in /private/var/folders/9r/3b500gbs3093ms87mqqbckr80000gn/T/pip-build-lqvxc68n/twisted/

运行openssl s_client -showcerts -connect pypi.python.org:443返回以下内容：

 CONNECTED(00000003)
 depth=1 /C=US/O=DigiCert Inc/OU=www.digicert.com/CN=DigiCert SHA2 Extended     Validation Server CA
 verify error:num=20:unable to get local issuer certificate
 verify return:0
 ---
 Certificate chain
  0 s:/businessCategory=Private Organization/1.3.6.1.4.1.311.60.2.1.3=US/1.3.6.1.4.1.311.60.2.1.2=Delaware/serialNumber=3359300/street=16 Allen    Rd/postalCode=03894-4801/C=US/ST=NH/L=Wolfeboro/O=Python Software Foundation/CN=www.python.org
  i:/C=US/O=DigiCert Inc/OU=www.digicert.com/CN=DigiCert SHA2 Extended Validation Server CA
  -----BEGIN CERTIFICATE-----
  MIIIWjCCB0KgAwIBAgIQCXCW7BLw16II/CMOsOFe/jANBgkqhkiG9w0BAQsFADB1
  ..
 -----END CERTIFICATE-----
 1 s:/C=US/O=DigiCert Inc/OU=www.digicert.com/CN=DigiCert SHA2 Extended Validation Server CA
 i:/C=US/O=DigiCert Inc/OU=www.digicert.com/CN=DigiCert High Assurance EV Root CA
 -----BEGIN CERTIFICATE-----
MIIEtjCCA56gAwIBAgIQDHmpRLCMEZUgkmFf4msdgzANBgkqhkiG9w0BAQsFADBs
....
-----END CERTIFICATE-----
 Server certificate
 subject=/businessCategory=Private Organization/1.3.6.1.4.1.311.60.2.1.3=US/1.3.6.1.4.1.311.60.2.1.2=Delaware/serialNumber=3359300/street=16 Allen Rd/postalCode=03894-4801/C=US/ST=NH/L=Wolfeboro/O=Python Software Foundation/CN=www.python.org
issuer=/C=US/O=DigiCert Inc/OU=www.digicert.com/CN=DigiCert SHA2 Extended  Validation Server CA
---
No client certificate CA names sent
---
SSL handshake has read 3524 bytes and written 456 bytes
---
New, TLSv1/SSLv3, Cipher is AES128-SHA
Server public key is 2048 bit
Secure Renegotiation IS supported
Compression: NONE
Expansion: NONE
SSL-Session:
Protocol  : TLSv1
Cipher    : AES128-SHA
Session-ID: BC7695FF86D2B82B20468A13E3F3E13AE23776B500E64665305EEBAF49BB54D1
Session-ID-ctx: 
Master-Key:8D25B34237A3C74E90317D87BA74A2AAF0E8C424FB2ADE3D72E5F234D5E043C4527641290B928B3A22 1BE7D44116CFB1
Key-Arg   : None
Start Time: 1487035770
Timeout   : 300 (sec)
Verify return code: 0 (ok)