Python3 ssl模块不可用的问题

编译安装完Python3之后，使用pip来安装python库，发现了如下报错：

$ pip install numpy
pip is configured with locations that require TLS/SSL, however the ssl module in Python is not available.
Collecting numpy
  Retrying (Retry(total=4, connect=None, read=None, redirect=None, status=None)) after connection broken by 'SSLError("Can't connect to HTTPS URL because the SSL module is not available.",)': /simple/numpy/
  Retrying (Retry(total=3, connect=None, read=None, redirect=None, status=None)) after connection broken by 'SSLError("Can't connect to HTTPS URL because the SSL module is not available.",)': /simple/numpy/
  Retrying (Retry(total=2, connect=None, read=None, redirect=None, status=None)) after connection broken by 'SSLError("Can't connect to HTTPS URL because the SSL module is not available.",)': /simple/numpy/
  Retrying (Retry(total=1, connect=None, read=None, redirect=None, status=None)) after connection broken by 'SSLError("Can't connect to HTTPS URL because the SSL module is not available.",)': /simple/numpy/
  Retrying (Retry(total=0, connect=None, read=None, redirect=None, status=None)) after connection broken by 'SSLError("Can't connect to HTTPS URL because the SSL module is not available.",)': /simple/numpy/
  Could not fetch URL https://pypi.python.org/simple/numpy/: There was a problem confirming the ssl certificate: HTTPSConnectionPool(host='pypi.python.org', port=443): Max retries exceeded with url: /simple/numpy/ (Caused by SSLError("Can't connect to HTTPS URL because the SSL module is not available.",)) - skipping
  Could not find a version that satisfies the requirement numpy (from versions: )
No matching distribution found for numpy

网上说了一种解决方案，是在./configure 的时候，加上--with-ssl选项，然后重新编译安装，尝试了下：

$ ./configure --with-ssl
... ...
configure: WARNING: unrecognized options: --with-ssl
... ...

出了个警告：不可识别的--with-ssl选项。

./configure --help看了下确实也没发现这个选项，估计是版本不一致，不大想折腾这个版本问题了，决定换个思路。

尝试安装openssl:

$ sudo yum install openssl

安装成功之后，重新编译安装，依旧报这个错，但是在make的时候有了一些发现：

$ make
... ...
Python build finished successfully!
The necessary bits to build these optional modules were not found:
_bz2                  _curses               _curses_panel      
_dbm                  _gdbm                 _lzma              
_sqlite3              _ssl                  _tkinter           
readline                                    
To find the necessary bits, look in setup.py in detect_modules() for the module's name.

可以看到，这里虽然make成功了，但是报了很多模块缺失，查看下编译安装目录下的setup.py，搜索_ssl，可以定位到如下代码：

 843         # Detect SSL support for the socket module (via _ssl)
 844         search_for_ssl_incs_in = [
 845                               '/usr/local/ssl/include',
 846                               '/usr/contrib/ssl/include/'
 847                              ]
 848         ssl_incs = find_file('openssl/ssl.h', inc_dirs,
 849                              search_for_ssl_incs_in
 850                              )
 851         if ssl_incs is not None:
 852             krb5_h = find_file('krb5.h', inc_dirs,
 853                                ['/usr/kerberos/include'])
 854             if krb5_h:
 855                 ssl_incs += krb5_h
 856         ssl_libs = find_library_file(self.compiler, 'ssl',lib_dirs,
 857                                      ['/usr/local/ssl/lib',
 858                                       '/usr/contrib/ssl/lib/'
 859                                      ] )
 860 
 861         if (ssl_incs is not None and
 862             ssl_libs is not None):
 863             exts.append( Extension('_ssl', ['_ssl.c'],
 864                                    include_dirs = ssl_incs,
 865                                    library_dirs = ssl_libs,
 866                                    libraries = ['ssl', 'crypto'],
 867                                    depends = ['socketmodule.h']), )
 868         else:
 869             missing.append('_ssl')

可以看到，setup.py会在'/usr/local/ssl/include', '/usr/contrib/ssl/include/' 这两个目录里面搜索'openssl/ssl.h' 这个头文件，然后会在 '/usr/local/ssl/lib' 和 '/usr/contrib/ssl/lib/' 之中搜索 ssl 的 lib文件，搜索不到，会将_ssl加入missing这个数组里面，然后寻找missing调用的地方：

 313         if missing:
 314             print()
 315             print("Python build finished successfully!")
 316             print("The necessary bits to build these optional modules were not "
 317                   "found:")
 318             print_three_column(missing)
 319             print("To find the necessary bits, look in setup.py in"
 320                   " detect_modules() for the module's name.")
 321             print()

找到了上面报错时候的输出，很明显，是由于搜索不到ssl.h头文件或者搜索不到lib文件而导致的报错，但是我刚刚明明是装了openssl的啊，为啥还会报找不到呢？手动搜索下：

$ sudo find / -name ssl.h

没找到ssl.h，折腾了一番之后，找到了如下命令：

$ sudo yum install zlib-devel bzip2-devel openssl-devel ncurses-devel sqlite-devel readline-devel tk-devel 

可以看到，这个命令安装的是openssl-devel，与我之前安装的openssl有所不同，查阅资料之后发现，openssl只包含了可执行部分，openssl-devel才包含了头文件、头文件参考、某些库文件等跟开发相关的东西。所以只安装openssl是找不到相应的头文件的，安装完之后，再次编译：

$ make clean
$ make
... ...
Python build finished successfully!
The necessary bits to build these optional modules were not found:
_dbm                  _gdbm                 _lzma              
To find the necessary bits, look in setup.py in detect_modules() for the module's name.

果然发现，缺失的模块少了很多。

继续安装：

$ sudo make install

安装完之后，重新执行pip:

$ pip install numpy
Collecting numpy
  Downloading https://files.pythonhosted.org/packages/68/1e/116ad560de97694e2d0c1843a7a0075cc9f49e922454d32f49a80eb6f1f2/numpy-1.14.5-cp36-cp36m-manylinux1_x86_64.whl (12.2MB)
    6% |██                              | 747kB 10kB/s eta 0:17:52

至此，pip安装报错的问题解决。