在MacOS下安装Python的Scrapy模块时出现这个错误提示：
error: command 'gcc' failed with exit status 1
网上找了很多方法，基本上都是Linux下的解决办法，试了几个都没有解决问题，最后解决的办法如下：
$ xcode-select --install
点击安装完成后再安装Scrapy就可以了：
$ pip3 install scrapy
参考来源：Scrapy安装指南 里面的 Mac OS X 安装指南
最后附上出错的安装过程及错误信息：
$ pip3 install scrapy
Collecting scrapy
Retrying (Retry(total=4, connect=None, read=None, redirect=None, status=None)) after connection broken by 'SSLError(SSLError("bad handshake: SysCallError(-1, 'Unexpected EOF')"))': /simple/scrapy/
Using cached https://files.pythonhosted.org/packages/3e/45/414e87ac8209d537c91575538c5307c20217a6943f555e0ee39f6db4bb0f/Scrapy-1.6.0-py2.py3-none-any.whl
Requirement already satisfied: parsel>=1.5 in /Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/site-packages (from scrapy) (1.5.1)
Requirement already satisfied: cssselect>=0.9 in /Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/site-packages (from scrapy) (1.0.3)
Requirement already satisfied: pyOpenSSL in /Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/site-packages (from scrapy) (19.0.0)
Requirement already satisfied: PyDispatcher>=2.0.5 in /Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/site-packages (from scrapy) (2.0.5)
Requirement already satisfied: lxml in /Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/site-packages (from scrapy) (4.2.5)
Requirement already satisfied: service-identity in /Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/site-packages (from scrapy) (18.1.0)
Collecting Twisted>=13.1.0 (from scrapy)
Using cached https://files.pythonhosted.org/packages/5d/0e/a72d85a55761c2c3ff1cb968143a2fd5f360220779ed90e0fadf4106d4f2/Twisted-18.9.0.tar.bz2
Requirement already satisfied: six>=1.5.2 in /Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/site-packages (from scrapy) (1.11.0)
Requirement already satisfied: queuelib in /Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/site-packages (from scrapy) (1.5.0)
Requirement already satisfied: w3lib>=1.17.0 in /Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/site-packages (from scrapy) (1.20.0)
Requirement already satisfied: cryptography>=2.3 in /Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/site-packages (from pyOpenSSL->scrapy) (2.3.1)
Requirement already satisfied: pyasn1 in /Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/site-packages (from service-identity->scrapy) (0.4.5)
Requirement already satisfied: pyasn1-modules in /Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/site-packages (from service-identity->scrapy) (0.2.4)
Requirement already satisfied: attrs>=16.0.0 in /Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/site-packages (from service-identity->scrapy) (18.2.0)
Requirement already satisfied: zope.interface>=4.4.2 in /Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/site-packages (from Twisted>=13.1.0->scrapy) (4.6.0)
Requirement already satisfied: constantly>=15.1 in /Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/site-packages (from Twisted>=13.1.0->scrapy) (15.1.0)
Requirement already satisfied: incremental>=16.10.1 in /Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/site-packages (from Twisted>=13.1.0->scrapy) (17.5.0)
Requirement already satisfied: Automat>=0.3.0 in /Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/site-packages (from Twisted>=13.1.0->scrapy) (0.7.0)
Requirement already satisfied: hyperlink>=17.1.1 in /Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/site-packages (from Twisted>=13.1.0->scrapy) (18.0.0)
Requirement already satisfied: PyHamcrest>=1.9.0 in /Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/site-packages (from Twisted>=13.1.0->scrapy) (1.9.0)
Requirement already satisfied: idna>=2.1 in /Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/site-packages (from cryptography>=2.3->pyOpenSSL->scrapy) (2.7)
Requirement already satisfied: cffi!=1.11.3,>=1.7 in /Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/site-packages (from cryptography>=2.3->pyOpenSSL->scrapy) (1.11.5)
Requirement already satisfied: asn1crypto>=0.21.0 in /Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/site-packages (from cryptography>=2.3->pyOpenSSL->scrapy) (0.24.0)
Requirement already satisfied: setuptools in /Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/site-packages (from zope.interface>=4.4.2->Twisted>=13.1.0->scrapy) (39.0.1)
Requirement already satisfied: pycparser in /Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/site-packages (from cffi!=1.11.3,>=1.7->cryptography>=2.3->pyOpenSSL->scrapy) (2.19)
Building wheels for collected packages: Twisted
Building wheel for Twisted (setup.py) ... error
Complete output from command /Library/Frameworks/Python.framework/Versions/3.7/bin/python3 -u -c "import setuptools, tokenize;__file__='/private/var/folders/tn/1d782flx6z11fczzvkj0cbkh0000gn/T/pip-install-x1v1zweo/Twisted/setup.py';f=getattr(tokenize, 'open', open)(__file__);code=f.read().replace('\r\n', '\n');f.close();exec(compile(code, __file__, 'exec'))" bdist_wheel -d /private/var/folders/tn/1d782flx6z11fczzvkj0cbkh0000gn/T/pip-wheel-l79nxuce --python-tag cp37:
running bdist_wheel
running build
running build_py
creating build
creating build/lib.macosx-10.9-x86_64-3.7
creating build/lib.macosx-10.9-x86_64-3.7/twisted
copying src/twisted/copyright.py -> build/lib.macosx-10.9-x86_64-3.7/twisted
（此处省略）...
copying src/twisted/internet/test/fake_CAs/thing2.pem -> build/lib.macosx-10.9-x86_64-3.7/twisted/internet/test/fake_CAs
running build_ext
building 'twisted.test.raiser' extension
creating build/temp.macosx-10.9-x86_64-3.7
creating build/temp.macosx-10.9-x86_64-3.7/src
creating build/temp.macosx-10.9-x86_64-3.7/src/twisted
creating build/temp.macosx-10.9-x86_64-3.7/src/twisted/test
gcc -Wno-unused-result -Wsign-compare -Wunreachable-code -fno-common -dynamic -DNDEBUG -g -fwrapv -O3 -Wall -arch x86_64 -g -I/Library/Frameworks/Python.framework/Versions/3.7/include/python3.7m -c src/twisted/test/raiser.c -o build/temp.macosx-10.9-x86_64-3.7/src/twisted/test/raiser.o
xcrun: error: invalid active developer path (/Library/Developer/CommandLineTools), missing xcrun at: /Library/Developer/CommandLineTools/usr/bin/xcrun
error: command 'gcc' failed with exit status 1
----------------------------------------
Command "/Library/Frameworks/Python.framework/Versions/3.7/bin/python3 -u -c "import setuptools, tokenize;__file__='/private/var/folders/tn/1d782flx6z11fczzvkj0cbkh0000gn/T/pip-install-x1v1zweo/Twisted/setup.py';f=getattr(tokenize, 'open', open)(__file__);code=f.read().replace('\r\n', '\n');f.close();exec(compile(code, __file__, 'exec'))" install --record /private/var/folders/tn/1d782flx6z11fczzvkj0cbkh0000gn/T/pip-record-ubp7cd5r/install-record.txt --single-version-externally-managed --compile" failed with error code 1 in /private/var/folders/tn/1d782flx6z11fczzvkj0cbkh0000gn/T/pip-install-x1v1zweo/Twisted/