安裝Python3
1.MAC下安裝python3
MAC下推薦使用homebrew來安裝Python3，什么是homebrew呢？
它是macOS 缺失的軟件包管理器。如何安裝homebrew，只需要在終端輸入：
/usr/bin/ruby -e "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/master/install)"
如果想進一步了解homebrew,點擊 homebrew官網
安裝完畢homebrew之后，開始安裝python3
1.1搜索包：
brew searsh python3
結果如下，說明存在python3的包，可以安裝。如圖 1-1
1.2安裝包：
brew install python3
控制臺輸入安裝過程如下：
==> Installing dependencies for python: gdbm, openssl, readline, sqlite, xz
==> Installing python dependency: gdbm
==> Downloading https://homebrew.bintray.com/bottles/gdbm-1.14.1_1.high_sierra.bottle.tar.gz
######################################################################## 100.0%
==> Pouring gdbm-1.14.1_1.high_sierra.bottle.tar.gz
?? /usr/local/Cellar/gdbm/1.14.1_1: 20 files, 555.7KB
==> Installing python dependency: openssl
==> Downloading https://homebrew.bintray.com/bottles/openssl-1.0.2o_1.high_sierra.bottle.tar.gz
######################################################################## 100.0%
==> Pouring openssl-1.0.2o_1.high_sierra.bottle.tar.gz
==> Caveats
A CA file has been bootstrapped using certificates from the SystemRoots
keychain. To add additional certificates (e.g. the certificates added in
the System keychain), place .pem files in
/usr/local/etc/openssl/certs
and run
/usr/local/opt/openssl/bin/c_rehash
This formula is keg-only, which means it was not symlinked into /usr/local,
because Apple has deprecated use of OpenSSL in favor of its own TLS and crypto libraries.
If you need to have this software first in your PATH run:
echo 'export PATH="/usr/local/opt/openssl/bin:$PATH"' >> ~/.bash_profile
For compilers to find this software you may need to set:
LDFLAGS: -L/usr/local/opt/openssl/lib
CPPFLAGS: -I/usr/local/opt/openssl/include
==> Summary
?? /usr/local/Cellar/openssl/1.0.2o_1: 1,791 files, 12.3MB
==> Installing python dependency: readline
==> Downloading https://homebrew.bintray.com/bottles/readline-7.0.3_1.high_sierra.bottle.tar.gz
######################################################################## 100.0%
==> Pouring readline-7.0.3_1.high_sierra.bottle.tar.gz
==> Caveats
This formula is keg-only, which means it was not symlinked into /usr/local,
because macOS provides the BSD libedit library, which shadows libreadline.
In order to prevent conflicts when programs look for libreadline we are
defaulting this GNU Readline installation to keg-only.
For compilers to find this software you may need to set:
LDFLAGS: -L/usr/local/opt/readline/lib
CPPFLAGS: -I/usr/local/opt/readline/include
==> Summary
?? /usr/local/Cellar/readline/7.0.3_1: 46 files, 1.5MB
==> Installing python dependency: sqlite
==> Downloading https://homebrew.bintray.com/bottles/sqlite-3.23.1.high_sierra.bottle.tar.gz
######################################################################## 100.0%
==> Pouring sqlite-3.23.1.high_sierra.bottle.tar.gz
==> Caveats
This formula is keg-only, which means it was not symlinked into /usr/local,
because macOS provides an older sqlite3.
If you need to have this software first in your PATH run:
echo 'export PATH="/usr/local/opt/sqlite/bin:$PATH"' >> ~/.bash_profile
For compilers to find this software you may need to set:
LDFLAGS: -L/usr/local/opt/sqlite/lib
CPPFLAGS: -I/usr/local/opt/sqlite/include
==> Summary
?? /usr/local/Cellar/sqlite/3.23.1: 11 files, 3MB
==> Installing python dependency: xz
==> Downloading https://homebrew.bintray.com/bottles/xz-5.2.4.high_sierra.bottle.tar.gz
######################################################################## 100.0%
==> Pouring xz-5.2.4.high_sierra.bottle.tar.gz
?? /usr/local/Cellar/xz/5.2.4: 92 files, 1MB
==> Installing python
==> Downloading https://homebrew.bintray.com/bottles/python-3.6.5.high_sierra.bottle.1.tar.gz
######################################################################## 100.0%
==> Pouring python-3.6.5.high_sierra.bottle.1.tar.gz
==> /usr/local/Cellar/python/3.6.5/bin/python3 -s setup.py --no-user-cfg install --force --verbose --install-scripts=/usr/local/C
==> /usr/local/Cellar/python/3.6.5/bin/python3 -s setup.py --no-user-cfg install --force --verbose --install-scripts=/usr/local/C
==> /usr/local/Cellar/python/3.6.5/bin/python3 -s setup.py --no-user-cfg install --force --verbose --install-scripts=/usr/local/C
==> Caveats
Python has been installed as
/usr/local/bin/python3
Unversioned symlinks python, python-config, pip etc. pointing to
python3, python3-config, pip3 etc., respectively, have been installed into
/usr/local/opt/python/libexec/bin
If you need Homebrew's Python 2.7 run
brew install python@2
Pip, setuptools, and wheel have been installed. To update them run
pip3 install --upgrade pip setuptools wheel
You can install Python packages with
pip3 install <package>
They will install into the site-package directory
/usr/local/lib/python3.6/site-packages
See: https://docs.brew.sh/Homebrew-and-Python
==> Summary
?? /usr/local/Cellar/python/3.6.5: 4,736 files, 99.2MB
1.3 檢測安裝是否成功。
打開終端，在命令行界面輸入分別python3 和pip -V 查看，如圖 1-2
安裝請求庫
爬蟲可以大致分為三個步驟：抓取頁面，分析頁面和存儲數據。
在抓取頁面的時候，我們需要模擬瀏覽器向服務器發送請求，這時需要用到一些python的庫來完成這些請求。常見的有：requests, Selenium和aiohttp等
安裝requests
requests是第三方庫，python默認不自帶這個庫，所以需要我們手動安裝這個模塊。相關參考資料1.Github | 2.PyPI | 3.官網文檔 | 4.中文文檔
使用pip安裝requets,執行：
pip3 install requests
驗證安裝，打開終端，在命令行中輸入：python3，進入命令行模式。
>>> import requests
如果什么錯誤提示有沒有，則證明安裝成功的安裝了requests。
安裝Selenium
Selenuim是一個自動化測試工具，利用它我們可以干什么呢？可以驅動瀏覽器執行特定的動作，例如點擊，下拉等操作。對于一些Javascript渲染的頁面來說，這種方式很有效。相關參考資料1.官方網站 | 2.Github | 3.PyPI | 4.中文文檔
使用pip安裝selenium,執行
pip3 install selenium
此時報錯了！！！錯誤信息
Could not install packages due to an EnvironmentError: [Errno 13] Permission denied: '/usr/local/selenium'
Consider using the `--user` option or check the permissions.
先把這個問題留在這里。
驗證安裝，打開終端，在命令行中輸入：python3,進入命令行模式。
>>> import selenium
沒有報錯，安裝成功！
