内容表

  • pprint — 数据美化打印机
    • 函数
    • PrettyPrinter 对象
    • 范例

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pprint — 数据美化打印机 ¶

源代码： Lib/pprint.py

The pprint 模块提供可以用作解释器输入形式的 pretty-print (美化打印) 任意 Python 数据结构的能力。若格式化的结构包括非基础 Python 类型的对象，表示可能无法被加载。若是包括文件、套接字或类的对象及许多无法表示成 Python 文字的其它对象，可能属于此情况。

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, adjustable by the width parameter defaulting to 80 characters.

字典按键排序在计算显示之前。

3.9 版改变： 添加支持为美化打印 types.SimpleNamespace .

3.10 版改变： 添加支持为美化打印 dataclasses.dataclass .

函数 ¶

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

打印格式化表示 object followed by a newline. If sort_dicts is false (the default), dictionaries will be displayed with their keys in insertion order, otherwise the dict keys will be sorted. args and kwargs 将被传递给 pprint() as formatting parameters. 

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

Added in version 3.8.

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

打印格式化表示 object on stream , followed by a newline. If stream is None , sys.stdout is used. This may be used in the interactive interpreter instead of the print() function for inspecting values (you can even reassign print = pprint.pprint for use within a scope).

The configuration parameters stream , indent , width , depth , compact , sort_dicts and underscore_numbers 被传递给 PrettyPrinter constructor and their meanings are as described in its documentation below.

注意， sort_dicts is True by default and you might want to use pp() instead where it is False 在默认情况下。

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

返回格式化表示 object 以字符串形式。 indent , width , depth , compact , sort_dicts and underscore_numbers 被传递给 PrettyPrinter constructor as formatting parameters and their meanings are as described in its documentation below.

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. This function is subject to the same limitations as noted in saferepr() below and may raise an RecursionError if it fails to detect a recursive object.

pprint. saferepr ( object ) ¶

返回字符串表示为 object , protected against recursion in some common data structures, namely instances of dict , list and tuple or subclasses whose __repr__ has not been overridden. 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 对象 ¶

This module defines one class:

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

构造 PrettyPrinter instance. This constructor understands several keyword parameters.

stream (默认 sys.stdout ) is a 像文件对象 to which the output will be written by calling its write() method. If both stream and sys.stdout are None ，那么 pprint() silently returns.

Other values configure the manner in which nesting of complex data structures is displayed.

indent (default 1) specifies the amount of indentation added for each nesting level.

depth controls the number of nesting levels which may be printed; if the data structure being printed is too deep, the next contained level is replaced by ... . By default, there is no constraint on the depth of the objects being formatted.

width (default 80) specifies the desired maximum number of characters per line in the output. If a structure cannot be formatted within the width constraint, a best effort will be made.

compact impacts the way that long sequences (lists, tuples, sets, etc) are formatted. If compact is false (the default) then each item of a sequence will be formatted on a separate line. If compact 为 True，将拟合尽可能多的项按 width will be formatted on each output line.

若 sort_dicts 为 True (默认)，字典将按其键次序被格式化，否则字典将按其键插入次序显示。

若 underscore_numbers is true, integers will be formatted with the _ character for a thousands separator, otherwise underscores are not displayed (the default).

3.4 版改变： 添加 compact 参数。

3.8 版改变： 添加 sort_dicts 参数。

3.10 版改变： 添加 underscore_numbers 参数。

3.11 版改变： No longer attempts to write to sys.stdout if it is None . 

>>> 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', (...)))))))

PrettyPrinter 实例具有下列方法：

PrettyPrinter. pformat ( object ) ¶

返回格式化表示 object . This takes into account the options passed to the PrettyPrinter 构造函数。

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 参数为 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() 实现。

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.

范例 ¶

To demonstrate several uses of the pp() 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, pp() shows the whole object: 

>>> pprint.pp(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.pp(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.pp(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'}

内容表

  • pprint — 数据美化打印机
    • 函数
    • PrettyPrinter 对象
    • 范例

上一话题

copy — 浅拷贝和深拷贝操作

下一话题

reprlib — 替代 repr() 实现

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  9. pprint — 数据美化打印机

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