Scrapy - OS X Homebrew Python错误

Question

我正在使用 OS X 版本 10.9.4。

我运行了 brew install python，但出现了以下错误……有人能告诉我发生了什么，以及我该怎么解决吗？

我在跟着这个教程：http://doc.scrapy.org/en/latest/intro/install.html（我最终是想下载 Scrapy。如果有人能提供一个比他们网站教程更详细的步骤，我会非常感激）

=> brew install python
==> Installing python dependency: readline
==> Downloading https://downloads.sf.net/project/machomebrew/Bottles/readline-6.3.8.mavericks.bottle.tar.gz
######################################################################## 100.0%
==> Pouring readline-6.3.8.mavericks.bottle.tar.gz
==> Caveats
This formula is keg-only, which means it was not symlinked into /usr/local.

Mac OS X provides similar software, and installing this software in
parallel can cause all kinds of trouble.

OS X provides the BSD libedit library, which shadows libreadline.
er to prevent conflicts when programs look for libreadline we are
ting this GNU Readline installation to keg-only.

Generally there are no consequences of this for you. If you build your
own software and it requires this formula, you'll need to add to your
build variables:

    LDFLAGS:  -L/usr/local/opt/readline/lib
    CPPFLAGS: -I/usr/local/opt/readline/include

==> Summary
  /usr/local/Cellar/readline/6.3.8: 40 files, 2.1M
==> Installing python
==> Downloading https://downloads.sf.net/project/machomebrew/Bottles/python-2.7.8_1.mavericks.bottle.2.tar.gz
######################################################################## 100.0%
==> Pouring python-2.7.8_1.mavericks.bottle.2.tar.gz
==> Caveats
Setuptools and Pip have been installed. To update them
  pip install --upgrade setuptools
  pip install --upgrade pip

You can install Python packages with
  pip install <package>

They will install into the site-package directory
  /usr/local/lib/python2.7/site-packages

See: https://github.com/Homebrew/homebrew/wiki/Homebrew-and-Python

.app bundles were installed.
Run `brew linkapps` to symlink these to /Applications.
Error: The `brew link` step did not complete successfully
The formula built, but is not symlinked into /usr/local
Could not symlink bin/2to3
Target /usr/local/bin/2to3
already exists. You may want to remove it:
  rm /usr/local/bin/2to3

To force the link and overwrite all conflicting files:
  brew link --overwrite python

To list all files that would be deleted:
  brew link --overwrite --dry-run python

Possible conflicting files are:
/usr/local/bin/2to3 -> /Library/Frameworks/Python.framework/Versions/2.7/bin/2to3
/usr/local/bin/2to3-2 -> /Library/Frameworks/Python.framework/Versions/2.7/bin/2to3-2
/usr/local/bin/2to3-2.7 -> /Library/Frameworks/Python.framework/Versions/2.7/bin/2to3-2.7
/usr/local/bin/idle -> /Library/Frameworks/Python.framework/Versions/2.7/bin/idle
/usr/local/bin/idle2 -> /Library/Frameworks/Python.framework/Versions/2.7/bin/idle2
/usr/local/bin/idle2.7 -> /Library/Frameworks/Python.framework/Versions/2.7/bin/idle2.7
/usr/local/bin/pydoc -> /Library/Frameworks/Python.framework/Versions/2.7/bin/pydoc
/usr/local/bin/pydoc2 -> /Library/Frameworks/Python.framework/Versions/2.7/bin/pydoc2
/usr/local/bin/pydoc2.7 -> /Library/Frameworks/Python.framework/Versions/2.7/bin/pydoc2.7
/usr/local/bin/python -> /Library/Frameworks/Python.framework/Versions/2.7/bin/python
/usr/local/bin/python-config -> /Library/Frameworks/Python.framework/Versions/2.7/bin/python-config
/usr/local/bin/python2 -> /Library/Frameworks/Python.framework/Versions/2.7/bin/python2
/usr/local/bin/python2-config -> /Library/Frameworks/Python.framework/Versions/2.7/bin/python2-config
/usr/local/bin/python2.7 -> /Library/Frameworks/Python.framework/Versions/2.7/bin/python2.7
/usr/local/bin/python2.7-config -> /Library/Frameworks/Python.framework/Versions/2.7/bin/python2.7-config
/usr/local/bin/pythonw -> /Library/Frameworks/Python.framework/Versions/2.7/bin/pythonw
/usr/local/bin/pythonw2 -> /Library/Frameworks/Python.framework/Versions/2.7/bin/pythonw2
/usr/local/bin/pythonw2.7 -> /Library/Frameworks/Python.framework/Versions/2.7/bin/pythonw2.7
/usr/local/bin/smtpd.py -> /Library/Frameworks/Python.framework/Versions/2.7/bin/smtpd.py
/usr/local/bin/smtpd2.7.py -> /Library/Frameworks/Python.framework/Versions/2.7/bin/smtpd2.7.py
/usr/local/bin/smtpd2.py -> /Library/Frameworks/Python.framework/Versions/2.7/bin/smtpd2.py
==> /usr/local/Cellar/python/2.7.8_1/bin/python -s setup.py --no-user-cfg install --force --verbose --install-scripts=/usr/local/Cellar/python/2.7.8_1/bin --install-lib=/usr/local/lib/python2.7/site-packa
==> /usr/local/Cellar/python/2.7.8_1/bin/python -s setup.py --no-user-cfg install --force --verbose --install-scripts=/usr/local/Cellar/python/2.7.8_1/bin --install-lib=/usr/local/lib/python2.7/site-packa
==> Summary
  /usr/local/Cellar/python/2.7.8_1: 4776 files, 76M

Answer 1

你的问题是，你已经在 /usr/local 安装了一个 Python 2.7（这个是在苹果预装的 /usr 里的 Python 2.7 之上）。最有可能的情况是，你是从 python.org 下载并运行了官方的安装程序。

因为 Homebrew 试图安装到 /usr/local，而同一个地方不能有两个同名的东西，所以它不允许你这样做。

如果你真的需要在系统上有三个 Python 2.7，你就得为其中一个选择一个不同的位置。注意，现有的那个其实只是指向 /Library/Frameworks/Python.framework/Versions/2.7/ 的一堆符号链接，而你想安装的新版本其实也是指向 /usr/local/Cellar/python/2.7.8 的一堆符号链接。所以，这些符号链接对任何一个来说其实都不是必须的。而且 Homebrew 让你不安装符号链接变得很简单：只要不执行 link 步骤就可以了。

当然，这意味着你不能直接用 pip 来为 Homebrew 的 Python 安装包，你得用 /usr/local/Cellar/python/2.7.8/bin/pip。而且你也得用 /usr/local/Cellar/python/2.7.8/bin/python 来 使用 Homebrew 的 Python。

不用说，你可以把 cellar 目录添加到你的 PATH 中……但这会让你更加困惑。你很容易就会遇到，比如说，PATH 中第一个 pip 是来自 Homebrew cellar，而第一个 ipython 是来自 python.org 的安装，这样你安装的东西却找不到——更糟糕的是，你的 pip 和 python-config 不匹配，导致每次需要 C 编译器的安装都出错。

所有这些都引出了一个问题：你为什么需要三个 Python 2.7 的版本（至少有两个在你的 PATH 中），更不用说两个版本了。如果你知道自己在做什么，倒是可以让它正常工作……但显然在这里并不是这样。那么，为什么要给自己制造麻烦呢？