# `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'}