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
pipis configured with locations that require TLS/SSL, however the ssl module in Python isnot 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 /simple/numpy/: There was a problem confirming the ssl certificate: HTTPSConnectionPool(host='', 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 (fromversions: )
No matching distribution foundfor 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, lookin 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,849search_for_ssl_incs_in850)851 if ssl_incs is notNone:852 krb5_h = find_file('krb5.h', inc_dirs,853 ['/usr/kerberos/include'])854 ifkrb5_h:855 ssl_incs +=krb5_h856 ssl_libs = find_library_file(piler, '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 notNone):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 ifmissing:314print()315 print("Python build finished successfully!")316 print("The necessary bits to build these optional modules were not"
317 "found:")318print_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 werenotfound:
_dbm _gdbm _lzma
To find the necessary bits, lookin 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 /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。
