"pprint" --- Data pretty printer
********************************

**Source code:** Lib/pprint.py

======================================================================

The "pprint" module provides a capability to "pretty-print" arbitrary
Python data structures in a form which can be used as input to the
interpreter. If the formatted structures include objects which are not
fundamental Python types, the representation may not be loadable.
This may be the case if objects such as files, sockets or classes are
included, as well as many other objects which are not representable as
Python literals.

The formatted representation keeps objects on a single line if it can,
and breaks them onto multiple lines if they don't fit within the
allowed width. Construct "PrettyPrinter" objects explicitly if you
need to adjust the width constraint.

Dictionaries are sorted by key before the display is computed.

The "pprint" module defines one class:

class pprint.PrettyPrinter(indent=1, width=80, depth=None, stream=None, *, compact=False, sort_dicts=True)

   构造一个 "PrettyPrinter" 实例。 此构造器接受几个关键字形参。 使用
   *stream* 关键字可设置输出流；流对象使用的唯一方法是文件协议的
   "write()" 方法。 如果未指定此关键字，则 "PrettyPrinter" 会选择
   "sys.stdout"。 每个递归层次的缩进量由 *indent* 指定；默认值为一。
   其他值可导致输出看起来有些怪异，，但可使得嵌套结构更易区分。 可被打
   印的层级数量由 *depth* 控制；如果数据结构的层级被打印得过深，其所包
   含的下一层级会被替换为 "..."。 在默认情况下，对被格式化对象的层级深
   度没有限制。 希望的输出宽度可使用 *width* 形参来限制；默认值为 80
   个字符。 如果一个结构无法在限定宽度内被格式化，则将做到尽可能接近。
   如果 *compact* 为假值（默认）则长序列的每一项将被格式化为单独的行。
   如果 *compact* 为真值，则将在 *width* 可容纳的的情况下把尽可能多的
   项放入每个输出行。 如果 *sort_dicts* 为真值（默认），字典将被格式化
   为按键排序，否则将按插入顺序显示。

   3.4 版更變: Added the *compact* parameter.

   3.8 版更變: 增加了 *sort_dicts* 形参。

   >>> import pprint
   >>> stuff = ['spam', 'eggs', 'lumberjack', 'knights', 'ni']
   >>> stuff.insert(0, stuff[:])
   >>> pp = pprint.PrettyPrinter(indent=4)
   >>> pp.pprint(stuff)
   [   ['spam', 'eggs', 'lumberjack', 'knights', 'ni'],
       'spam',
       'eggs',
       'lumberjack',
       'knights',
       'ni']
   >>> pp = pprint.PrettyPrinter(width=41, compact=True)
   >>> pp.pprint(stuff)
   [['spam', 'eggs', 'lumberjack',
     'knights', 'ni'],
    'spam', 'eggs', 'lumberjack', 'knights',
    'ni']
   >>> tup = ('spam', ('eggs', ('lumberjack', ('knights', ('ni', ('dead',
   ... ('parrot', ('fresh fruit',))))))))
   >>> pp = pprint.PrettyPrinter(depth=6)
   >>> pp.pprint(tup)
   ('spam', ('eggs', ('lumberjack', ('knights', ('ni', ('dead', (...)))))))

The "pprint" module also provides several shortcut functions:

pprint.pformat(object, indent=1, width=80, depth=None, *, compact=False, sort_dicts=True)

   *object* 的格式化表示作为字符串返回。 *indent*, *width*, *depth*,
   *compact* 和 *sort_dicts* 将作为格式化形参被传入 "PrettyPrinter" 构
   造器。

   3.4 版更變: Added the *compact* parameter.

   3.8 版更變: 增加了 *sort_dicts* 形参。

pprint.pp(object, *args, sort_dicts=False, **kwargs)

   打印 *object* 的格式化表示并附带一个换行符。 如果 *sort_dicts* 为假
   值（默认），字典将按键的插入顺序显示，否则将按字典键排序。 *args*
   和 *kwargs* 将作为格式化形参被传给 "pprint()"。

   3.8 版新加入.

pprint.pprint(object, stream=None, indent=1, width=80, depth=None, *, compact=False, sort_dicts=True)

   在 *stream* 上打打印 *object* 的格式化表示，并附带一个换行符。 如果
   *stream* 为 "None"，则使用 "sys.stdout"。 这可以替代 "print()" 函数
   在交互式解释器中使用以查看值（你甚至可以执行重新赋值 "print =
   pprint.pprint" 以在特定作用域中使用）。 *indent*, *width*, *depth*,
   *compact* 和 *sort_dicts* 将作为格式化形参被传给 "PrettyPrinter" 构
   造器。

   3.4 版更變: Added the *compact* parameter.

   3.8 版更變: 增加了 *sort_dicts* 形参。

   >>> import pprint
   >>> stuff = ['spam', 'eggs', 'lumberjack', 'knights', 'ni']
   >>> stuff.insert(0, stuff)
   >>> pprint.pprint(stuff)
   [<Recursion on list with id=...>,
    'spam',
    'eggs',
    'lumberjack',
    'knights',
    'ni']

pprint.isreadable(object)

   Determine if the formatted representation of *object* is
   "readable," or can be used to reconstruct the value using "eval()".
   This always returns "False" for recursive objects.

   >>> pprint.isreadable(stuff)
   False

pprint.isrecursive(object)

   Determine if *object* requires a recursive representation.

One more support function is also defined:

pprint.saferepr(object)

   Return a string representation of *object*, protected against
   recursive data structures.  If the representation of *object*
   exposes a recursive entry, the recursive reference will be
   represented as "<Recursion on typename with id=number>".  The
   representation is not otherwise formatted.

   >>> pprint.saferepr(stuff)
   "[<Recursion on list with id=...>, 'spam', 'eggs', 'lumberjack', 'knights', 'ni']"


PrettyPrinter Objects
=====================

"PrettyPrinter" instances have the following methods:

PrettyPrinter.pformat(object)

   Return the formatted representation of *object*.  This takes into
   account the options passed to the "PrettyPrinter" constructor.

PrettyPrinter.pprint(object)

   Print the formatted representation of *object* on the configured
   stream, followed by a newline.

The following methods provide the implementations for the
corresponding functions of the same names.  Using these methods on an
instance is slightly more efficient since new "PrettyPrinter" objects
don't need to be created.

PrettyPrinter.isreadable(object)

   Determine if the formatted representation of the object is
   "readable," or can be used to reconstruct the value using "eval()".
   Note that this returns "False" for recursive objects.  If the
   *depth* parameter of the "PrettyPrinter" is set and the object is
   deeper than allowed, this returns "False".

PrettyPrinter.isrecursive(object)

   Determine if the object requires a recursive representation.

This method is provided as a hook to allow subclasses to modify the
way objects are converted to strings.  The default implementation uses
the internals of the "saferepr()" implementation.

PrettyPrinter.format(object, context, maxlevels, level)

   Returns three values: the formatted version of *object* as a
   string, a flag indicating whether the result is readable, and a
   flag indicating whether recursion was detected.  The first argument
   is the object to be presented.  The second is a dictionary which
   contains the "id()" of objects that are part of the current
   presentation context (direct and indirect containers for *object*
   that are affecting the presentation) as the keys; if an object
   needs to be presented which is already represented in *context*,
   the third return value should be "True".  Recursive calls to the
   "format()" method should add additional entries for containers to
   this dictionary.  The third argument, *maxlevels*, gives the
   requested limit to recursion; this will be "0" if there is no
   requested limit.  This argument should be passed unmodified to
   recursive calls. The fourth argument, *level*, gives the current
   level; recursive calls should be passed a value less than that of
   the current call.


Example
=======

To demonstrate several uses of the "pprint()" function and its
parameters, let's fetch information about a project from PyPI:

   >>> import json
   >>> import pprint
   >>> from urllib.request import urlopen
   >>> with urlopen('https://pypi.org/pypi/sampleproject/json') as resp:
   ...     project_info = json.load(resp)['info']

In its basic form, "pprint()" shows the whole object:

   >>> pprint.pprint(project_info)
   {'author': 'The Python Packaging Authority',
    'author_email': 'pypa-dev@googlegroups.com',
    'bugtrack_url': None,
    'classifiers': ['Development Status :: 3 - Alpha',
                    'Intended Audience :: Developers',
                    'License :: OSI Approved :: MIT License',
                    'Programming Language :: Python :: 2',
                    'Programming Language :: Python :: 2.6',
                    'Programming Language :: Python :: 2.7',
                    'Programming Language :: Python :: 3',
                    'Programming Language :: Python :: 3.2',
                    'Programming Language :: Python :: 3.3',
                    'Programming Language :: Python :: 3.4',
                    'Topic :: Software Development :: Build Tools'],
    'description': 'A sample Python project\n'
                   '=======================\n'
                   '\n'
                   'This is the description file for the project.\n'
                   '\n'
                   'The file should use UTF-8 encoding and be written using '
                   'ReStructured Text. It\n'
                   'will be used to generate the project webpage on PyPI, and '
                   'should be written for\n'
                   'that purpose.\n'
                   '\n'
                   'Typical contents for this file would include an overview of '
                   'the project, basic\n'
                   'usage examples, etc. Generally, including the project '
                   'changelog in here is not\n'
                   'a good idea, although a simple "What\'s New" section for the '
                   'most recent version\n'
                   'may be appropriate.',
    'description_content_type': None,
    'docs_url': None,
    'download_url': 'UNKNOWN',
    'downloads': {'last_day': -1, 'last_month': -1, 'last_week': -1},
    'home_page': 'https://github.com/pypa/sampleproject',
    'keywords': 'sample setuptools development',
    'license': 'MIT',
    'maintainer': None,
    'maintainer_email': None,
    'name': 'sampleproject',
    'package_url': 'https://pypi.org/project/sampleproject/',
    'platform': 'UNKNOWN',
    'project_url': 'https://pypi.org/project/sampleproject/',
    'project_urls': {'Download': 'UNKNOWN',
                     'Homepage': 'https://github.com/pypa/sampleproject'},
    'release_url': 'https://pypi.org/project/sampleproject/1.2.0/',
    'requires_dist': None,
    'requires_python': None,
    'summary': 'A sample Python project',
    'version': '1.2.0'}

The result can be limited to a certain *depth* (ellipsis is used for
deeper contents):

   >>> pprint.pprint(project_info, depth=1)
   {'author': 'The Python Packaging Authority',
    'author_email': 'pypa-dev@googlegroups.com',
    'bugtrack_url': None,
    'classifiers': [...],
    'description': 'A sample Python project\n'
                   '=======================\n'
                   '\n'
                   'This is the description file for the project.\n'
                   '\n'
                   'The file should use UTF-8 encoding and be written using '
                   'ReStructured Text. It\n'
                   'will be used to generate the project webpage on PyPI, and '
                   'should be written for\n'
                   'that purpose.\n'
                   '\n'
                   'Typical contents for this file would include an overview of '
                   'the project, basic\n'
                   'usage examples, etc. Generally, including the project '
                   'changelog in here is not\n'
                   'a good idea, although a simple "What\'s New" section for the '
                   'most recent version\n'
                   'may be appropriate.',
    'description_content_type': None,
    'docs_url': None,
    'download_url': 'UNKNOWN',
    'downloads': {...},
    'home_page': 'https://github.com/pypa/sampleproject',
    'keywords': 'sample setuptools development',
    'license': 'MIT',
    'maintainer': None,
    'maintainer_email': None,
    'name': 'sampleproject',
    'package_url': 'https://pypi.org/project/sampleproject/',
    'platform': 'UNKNOWN',
    'project_url': 'https://pypi.org/project/sampleproject/',
    'project_urls': {...},
    'release_url': 'https://pypi.org/project/sampleproject/1.2.0/',
    'requires_dist': None,
    'requires_python': None,
    'summary': 'A sample Python project',
    'version': '1.2.0'}

Additionally, maximum character *width* can be suggested. If a long
object cannot be split, the specified width will be exceeded:

   >>> pprint.pprint(project_info, depth=1, width=60)
   {'author': 'The Python Packaging Authority',
    'author_email': 'pypa-dev@googlegroups.com',
    'bugtrack_url': None,
    'classifiers': [...],
    'description': 'A sample Python project\n'
                   '=======================\n'
                   '\n'
                   'This is the description file for the '
                   'project.\n'
                   '\n'
                   'The file should use UTF-8 encoding and be '
                   'written using ReStructured Text. It\n'
                   'will be used to generate the project '
                   'webpage on PyPI, and should be written '
                   'for\n'
                   'that purpose.\n'
                   '\n'
                   'Typical contents for this file would '
                   'include an overview of the project, '
                   'basic\n'
                   'usage examples, etc. Generally, including '
                   'the project changelog in here is not\n'
                   'a good idea, although a simple "What\'s '
                   'New" section for the most recent version\n'
                   'may be appropriate.',
    'description_content_type': None,
    'docs_url': None,
    'download_url': 'UNKNOWN',
    'downloads': {...},
    'home_page': 'https://github.com/pypa/sampleproject',
    'keywords': 'sample setuptools development',
    'license': 'MIT',
    'maintainer': None,
    'maintainer_email': None,
    'name': 'sampleproject',
    'package_url': 'https://pypi.org/project/sampleproject/',
    'platform': 'UNKNOWN',
    'project_url': 'https://pypi.org/project/sampleproject/',
    'project_urls': {...},
    'release_url': 'https://pypi.org/project/sampleproject/1.2.0/',
    'requires_dist': None,
    'requires_python': None,
    'summary': 'A sample Python project',
    'version': '1.2.0'}
