Python之pip安装失败：ReadTimeoutError: HTTPSConnectionPool(host=“xxx'', port=): Read timed out.

今天安装opencv-python时，出现错误提示：

ReadTimeoutError: HTTPSConnectionPool(host='files.pythonhosted.org', port=443): Read timed out.

网上查了下，可能是网络的原因，导致连接资源超时了，只要自定义连接延迟时间就可以解决。

So，更改pip安装命令如下：

pip3 install --default-timeout=100 opencv-python

搞定。

附：

pip install 帮助文档：

panpandeMacBook-Pro:~ panpan$ pip install --help

Usage:   
  pip install [options]  [package-index-options] ...
  pip install [options] -r  [package-index-options] ...
  pip install [options] [-e]  ...
  pip install [options] [-e]  ...
  pip install [options]  ...

Description:
  Install packages from:
  
  - PyPI (and other indexes) using requirement specifiers.
  - VCS project urls.
  - Local project directories.
  - Local or remote source archives.
  
  pip also supports installing from "requirements files", which provide
  an easy way to specify a whole environment to be installed.

Install Options:
  -r, --requirement     Install from the given requirements file. This option can be used multiple times.
  -c, --constraint      Constrain versions using the given constraints file. This option can be used multiple times.
  --no-deps                   Don't install package dependencies.
  --pre                       Include pre-release and development versions. By default, pip only finds stable versions.
  -e, --editable    Install a project in editable mode (i.e. setuptools "develop mode") from a local project path or a VCS url.
  -t, --target           Install packages into . By default this will not replace existing files/folders in . Use --upgrade to replace existing packages in  with new versions.
  --platform        Only use wheels compatible with . Defaults to the platform of the running system.
  --python-version 
                              Only use wheels compatible with Python interpreter version . If not specified, then the current system interpreter minor version is used. A major version (e.g. '2') can be specified to
                              match all minor revs of that major version.  A minor version (e.g. '34') can also be specified.
  --implementation 
                              Only use wheels compatible with Python implementation , e.g. 'pp', 'jy', 'cp',  or 'ip'. If not specified, then the current interpreter implementation is used.  Use 'py' to
                              force implementation-agnostic wheels.
  --abi                  Only use wheels compatible with Python abi , e.g. 'pypy_41'.  If not specified, then the current interpreter abi tag is used.  Generally you will need to specify --implementation,
                              --platform, and --python-version when using this option.
  --user                      Install to the Python user install directory for your platform. Typically ~/.local/, or %APPDATA%\Python on Windows. (See the Python documentation for site.USER_BASE for full details.)
  --root                 Install everything relative to this alternate root directory.
  --prefix               Installation prefix where lib, bin and other top-level folders are placed
  -b, --build            Directory to unpack packages into and build in. Note that an initial build still takes place in a temporary directory. The location of temporary directories can be controlled by setting the
                              TMPDIR environment variable (TEMP on Windows) appropriately. When passed, build directories are not cleaned in case of failures.
  --src                  Directory to check out editable projects into. The default in a virtualenv is "/src". The default for global installs is "/src".
  -U, --upgrade               Upgrade all specified packages to the newest available version. The handling of dependencies depends on the upgrade-strategy used.
  --upgrade-strategy 
                              Determines how dependency upgrading should be handled [default: only-if-needed]. "eager" - dependencies are upgraded regardless of whether the currently installed version satisfies the
                              requirements of the upgraded package(s). "only-if-needed" -  are upgraded only when they do not satisfy the requirements of the upgraded package(s).
  --force-reinstall           Reinstall all packages even if they are already up-to-date.
  -I, --ignore-installed      Ignore the installed packages (reinstalling instead).
  --ignore-requires-python    Ignore the Requires-Python information.
  --no-build-isolation        Disable isolation when building a modern source distribution. Build dependencies specified by PEP 518 must be already installed if this option is used.
  --use-pep517                Use PEP 517 for building source distributions (use --no-use-pep517 to force legacy behaviour).
  --install-option   Extra arguments to be supplied to the setup.py install command (use like --install-option="--install-scripts=/usr/local/bin"). Use multiple --install-option options to pass multiple options to
                              setup.py install. If you are using an option with a directory path, be sure to use absolute path.
  --global-option    Extra global options to be supplied to the setup.py call before the install command.
  --compile                   Compile Python source files to bytecode
  --no-compile                Do not compile Python source files to bytecode
  --no-warn-script-location   Do not warn when installing scripts outside PATH
  --no-warn-conflicts         Do not warn about broken dependencies
  --no-binary 
                              Do not use binary packages. Can be supplied multiple times, and each time adds to the existing value. Accepts either :all: to disable all binary packages, :none: to empty the set, or one or
                              more package names with commas between them. Note that some packages are tricky to compile and may fail to install when this option is used on them.
  --only-binary 
                              Do not use source packages. Can be supplied multiple times, and each time adds to the existing value. Accepts either :all: to disable all source packages, :none: to empty the set, or one or
                              more package names with commas between them. Packages without binary distributions will fail to install when this option is used on them.
  --prefer-binary             Prefer older binary packages over newer source packages.
  --no-clean                  Don't clean up build directories.
  --require-hashes            Require a hash to check each requirement against, for repeatable installs. This option is implied when any package in a requirements file has a --hash option.
  --progress-bar 
                              Specify type of progress to be displayed [on|ascii|off|pretty|emoji] (default: on)

Package Index Options:
  -i, --index-url        Base URL of Python Package Index (default https://pypi.org/simple). This should point to a repository compliant with PEP 503 (the simple repository API) or a local directory laid out in the
                              same format.
  --extra-index-url      Extra URLs of package indexes to use in addition to --index-url. Should follow the same rules as --index-url.
  --no-index                  Ignore package index (only looking at --find-links URLs instead).
  -f, --find-links       If a url or path to an html file, then parse for links to archives. If a local path or file:// url that's a directory, then look for archives in the directory listing.

General Options:
  -h, --help                  Show help.
  --isolated                  Run pip in an isolated mode, ignoring environment variables and user configuration.
  -v, --verbose               Give more output. Option is additive, and can be used up to 3 times.
  -V, --version               Show version and exit.
  -q, --quiet                 Give less output. Option is additive, and can be used up to 3 times (corresponding to WARNING, ERROR, and CRITICAL logging levels).
  --log                 Path to a verbose appending log.
  --proxy              Specify a proxy in the form [user:passwd@]proxy.server:port.
  --retries          Maximum number of retries each connection should attempt (default 5 times).
  --timeout              Set the socket timeout (default 15 seconds).
  --exists-action     Default action when a path already exists: (s)witch, (i)gnore, (w)ipe, (b)ackup, (a)bort.
  --trusted-host    Mark this host as trusted, even though it does not have valid or any HTTPS.
  --cert                Path to alternate CA bundle.
  --client-cert         Path to SSL client certificate, a single file containing the private key and the certificate in PEM format.
  --cache-dir            Store the cache data in .
  --no-cache-dir              Disable the cache.
  --disable-pip-version-check
                              Don't periodically check PyPI to determine whether a new version of pip is available for download. Implied with --no-index.
  --no-color                  Suppress colored output