【Python入门】Python入门常见疑问

参考文章

• pip vs easy_install
• Why use pip over easy_install?
• Wheel vs Egg

1. pip vs easy_install

• Python Packaging User Guide的见解

easy_install was released in 2004, as part of setuptools. It was notable at the time for installing packages from PyPI using requirement specifiers, and automatically installing dependencies.

pip came later in 2008, as alternative to easy_install, although still largely built on top of setuptools components. It was notable at the time for not installing packages as Eggs or from Eggs (but rather simply as ‘flat’ packages from sdists), and introducing the idea of Requirements Files, which gave users the power to easily replicate environments.

Here’s a breakdown of the important differences between pip and easy_install now:

	pip	easy_install
Install from Wheels	Yes	No
Uninstall Packages	Yes(pip uninstall)	No
Dependency Overrides	Yes(Requirements)	No
List Installed Packages	Yes(pip list and pip freeze)	No
PEP 438 Support	Yes	No
Installation format	'Flat' packages with egg-info metadata.	Encapsulated Egg format
sys.path modification	No	Yes
Installs from Eggs	No	Yes
pylaucher support	No	Yes
Multi-version Installs	No	Yes
Exclude scripts during install	No	Yes

• StackOverFlow 上一个答案的见解

Many of the answers here are out of date for 2015 (although the initially accepted one from Daniel Roseman is not). Here's the current state of things:

• Binary packages are now distributed as wheels (.whl files)—not just on PyPI, but in third-party repositories like Christoph Gohlke's Extension Packages for Windows. pip can handle wheels; easy_install cannot.

• Virtual environments (which come built-in with 3.4, or can be added to 2.6+/3.1+ with virtualenv) have become a very important and prominent tool (and recommended in the official docs); they include pip out of the box, but don't even work properly with easy_install.

• The distribute package that included easy_install is no longer maintained. Its improvements over setuptools got merged back into setuptools. Trying to install distribute will just install setuptools instead.

• easy_install itself is only quasi-maintained.

• All of the cases where pip used to be inferior to easy_install—installing from an unpacked source tree, from a DVCS repo, etc.—are long-gone; you can pip install ., pip install git+https://.

• pip comes with the official Python 2.7 and 3.4+ packages from python.org, and a pip bootstrap is included by default if you build from source.

• The various incomplete bits of documentation on installing, using, and building packages have been replaced by the Python Packaging User Guide. Python's own documentation on Installing Python Modules now defers to this user guide, and explicitly calls out pip as "the preferred installer program".

• Other new features have been added to pip over the years that will never be in easy_install. For example, pip makes it easy to clone your site-packages by building a requirements file and then installing it with a single command on each side. Or to convert your requirements file to a local repo to use for in-house development. And so on.

The only good reason that I know of to use easy_install in 2015 is the special case of using Apple's pre-installed Python versions with OS X 10.5-10.8. Since 10.5, Apple has included easy_install, but as of 10.10 they still don't include pip. With 10.9+, you should still just use get-pip.py, but for 10.5-10.8, this has some problems, so it's easier to sudo easy_install pip. (In general, easy_install pip is a bad idea; it's only for OS X 10.5-10.8 that you want to do this.) Also, 10.5-10.8 include readline in a way that easy_install knows how to kludge around but pip doesn't, so you also want to sudo easy_install readline if you want to upgrade that.

2. Wheel vs Egg

Wheel and Egg are both packaging formats that aim to support the use case of needing an install artifact that doesn’t require building or compilation, which can be costly in testing and production workflows.

The Egg format was introduced by setuptools in 2004, whereas the Wheel format was introduced by PEP 427 in 2012.

Wheel is currently considered the standard for built and binary packaging for Python.

Here’s a breakdown of the important differences between Wheel and Egg.

• Wheel has an official PEP, Egg did not.
• Wheel is a distribution format, i.e a packaging format. Egg was both a distribution format and a runtime installation format (if left zipped), and was designed to be importable.
• Wheel archives do not include .pyc files. Therefore, when the distribution only contains python files (i.e. no compiled extensions), and is compatible with Python 2 and 3, it’s possible for a wheel to be “universal”, similar to an sdist.
• Wheel uses PEP376-compliant .dist-info directories, Egg used .egg-info.
• Wheel has a richer file naming convention. A single wheel archive can indicate its compatibility with a number of Python language versions and implementations, ABIs, and system architectures.
• Wheel is versioned. Every wheel file contains the version of the wheel specification and the implementation that packaged it.
• Wheel is internally organized by sysconfig path type, therefore making it easier to convert to other formats.