管理渠道#

Conda 渠道（channels）是存放软件包的位置，它们是托管和管理 Conda 软件包的基础。 Conda 软件包会从远程渠道下载，这些远程渠道本质上是包含 Conda 包的目录的 URL。 conda 命令会搜索一组默认渠道，并自动从 default channel 下载和更新软件包。 关于 conda 渠道 及其使用条款的更多信息请参考相关文档。

不同渠道可能包含同名的软件包，因此 Conda 必须处理所谓的 渠道冲突 （channel collisions）。

如果你只使用默认渠道（defaults），就不会发生渠道冲突。 如果你使用的所有渠道中的包互不重叠（即没有重复的包名），也不会有冲突。 当多个渠道列表中包含同名软件包时，Conda 的冲突解决机制才会生效。

默认情况下，Conda 会 优先选择高优先级渠道 中的软件包，而不是低优先级渠道中的版本。 这意味着你可以安心地将非默认渠道放在渠道列表的后面，从中获取默认渠道中没有的额外软件包， 同时又不担心这些渠道会覆盖核心软件包。

Conda 会从所有列出的渠道中收集同名软件包，并按以下顺序处理：

1. 按照 渠道优先级从高到低 对包进行排序。

2. 对于渠道优先级相同的包，按 版本号从高到低 排序。例如，如果 channelA 提供 NumPy 1.12.0 和 1.13.1，后者优先。

3. 如果版本号也相同，则按 构建号从高到低 排序。例如，如果 channelA 提供 NumPy 1.12.0 build 1 和 build 2，则 build 2 优先。channelB 的所有 NumPy 包将排在 channelA 的之后。

4. 安装排序列表中第一个满足安装条件的包。

简而言之，排序优先级如下：

channelA::numpy-1.13_1 > channelA::numpy-1.12.1_1 > channelA::numpy-1.12.1_0 > channelB::numpy-1.13_1

若希望 Conda 安装所列渠道中**最新版本**的软件包：

• 可将以下内容添加至你的 .condarc 文件：

  channel_priority: disabled

• 或运行以下等效命令:

  conda config --set channel_priority disabled
  

此时 Conda 的排序机制如下：

1. 按 版本号从高到低 排序。

2. 对版本相同的包，按 渠道优先级从高到低 排序。

3. 若渠道优先级和版本都相同，按 构建号从高到低 排序。

注意：不同渠道间的构建号不可比较，因此构建号始终排在渠道优先级之后。

以下命令会将 new_channel 添加到渠道列表顶部，使其成为最高优先级渠道:

conda config --add channels new_channel

等效命令是:

conda config --prepend channels new_channel

而如果你想将其添加到列表底部（最低优先级），可使用:

conda config --append channels new_channel

Conda channels are the locations where packages are stored. They serve as the base for hosting and managing packages. Conda packages are downloaded from remote channels, which are URLs to directories containing conda packages. The conda command searches a default set of channels and packages are automatically downloaded and updated from the default channel. Read more about conda channels and the various terms of service for their use.

Different channels can have the same package, so conda must handle these channel collisions.

There will be no channel collisions if you use only the defaults channel. There will also be no channel collisions if all of the channels you use only contain packages that do not exist in any of the other channels in your list. The way conda resolves these collisions matters only when you have multiple channels in your channel list that host the same package.

By default, conda prefers packages from a higher priority channel over any version from a lower priority channel. Therefore, you can now safely put channels at the bottom of your channel list to provide additional packages that are not in the default channels and still be confident that these channels will not override the core package set.

Conda collects all of the packages with the same name across all listed channels and processes them as follows:

1. Sorts packages from highest to lowest channel priority.

2. Sorts tied packages---packages with the same channel priority---from highest to lowest version number. For example, if channelA contains NumPy 1.12.0 and 1.13.1, NumPy 1.13.1 will be sorted higher.

3. Sorts still-tied packages---packages with the same channel priority and same version---from highest to lowest build number. For example, if channelA contains both NumPy 1.12.0 build 1 and build 2, build 2 is sorted first. Any packages in channelB would be sorted below those in channelA.

4. Installs the first package on the sorted list that satisfies the installation specifications.

Essentially, the order goes: channelA::numpy-1.13_1 > channelA::numpy-1.12.1_1 > channelA::numpy-1.12.1_0 > channelB::numpy-1.13_1

To make conda install the newest version of a package in any listed channel:

• Add channel_priority: disabled to your .condarc file.

  OR

• Run the equivalent command:

  conda config --set channel_priority disabled
  

Conda then sorts as follows:

1. Sorts the package list from highest to lowest version number.

2. Sorts tied packages from highest to lowest channel priority.

3. Sorts tied packages from highest to lowest build number.

Because build numbers from different channels are not comparable, build number still comes after channel priority.

The following command adds the channel "new_channel" to the top of the channel list, making it the highest priority:

conda config --add channels new_channel

Conda has an equivalent command:

conda config --prepend channels new_channel

Conda also has a command that adds the new channel to the bottom of the channel list, making it the lowest priority:

conda config --append channels new_channel