好程序员Python培训技术分享用pprint代替print更友好的打印调试信息

　　pprint 是 “pretty printer” 的简写，“pretty” 的含义是 “漂亮的、美观的”，因此 pprint 的含义便是：漂亮的打印。

这是个相当简单却有用的模块，主要用于打印复杂的数据结构对象，例如多层嵌套的列表、元组和字典等。

先看看 print() 打印的一个例子：

python

mylist = ["Beautiful is better than ugly.", "Explicit is better than implicit.", "Simple is better than complex.", "Complex is better than complicated."]

print(mylist)

['Beautiful is better than ugly.', 'Explicit is better than implicit.', 'Simple is better than complex.', 'Complex is better than complicated.']

这是一个简单的例子，全部打印在一行里。如果对象中的元素是多层嵌套的内容（例如复杂的 字典 数据），再打印出那肯定是一团糟的，不好阅读。

使用 pprint 模块的 pprint() 替代 print()，可以解决如下痛点：

- **设置合适的行宽度，作适当的换行**

- **设置打印的缩进、层级，进行格式化打印**

- **判断对象中是否有无限循环，并优化打印内容**

基本使用

python

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

默认的行宽度参数为 80，当打印的字符小于 80 时，pprint() 基本上等同于内置函数 print()，当字符超出时，它会作美化，进行格式化输出。

python

import pprint

mylist = ["Beautiful is better than ugly.", "Explicit is better than implicit.", "Simple is better than complex.", "Complex is better than complicated."]

pprint.pprint(mylist)

超出80字符，打印的元素是换行的

['Beautiful is better than ugly.',

 'Explicit is better than implicit.',

 'Simple is better than complex.',

 'Complex is better than complicated.']

设置缩进

python

pprint.pprint(mylist, indent=4)

[   'Beautiful is better than ugly.',

    'Explicit is better than implicit.',

    'Simple is better than complex.',

    'Complex is better than complicated.']

设置打印行宽

python

  mydict = {'students': [{'name':'Tom', 'age': 18},{'name':'Jerry', 'age': 19}]}

  pprint.pprint(mydict)

  正常打印

  {'students': [{'age': 18, 'name': 'Tom'}, {'age': 19, 'name': 'Jerry'}]}

  pprint.pprint(mydict, width=20)

  行宽为 20

  {'students': [{'age': 18,

                 'name': 'Tom'},

                {'age': 19,

                 'name': 'Jerry'}]}

  pprint.pprint(mydict, width=70)

  行宽为 70

  {'students': [{'age': 18, 'name': 'Tom'},

                {'age': 19, 'name': 'Jerry'}]}

  ```

设置打印层级

python

newlist = [1, [2, [3, [4, [5]]]]]

pprint.pprint(newlist, depth=3)

超出的层级会用 ... 表示

[1, [2, [3, [...]]]]

用 pprint 替换 print

python

import pprint

print = pprint.pprint

mylist = ["Beautiful is better than ugly.", "Explicit is better than implicit.", "Simple is better than complex.", "Complex is better than complicated."]

print(mylist)

['Beautiful is better than ugly.',

 'Explicit is better than implicit.',

 'Simple is better than complex.',

 'Complex is better than complicated.']

更多用法请查看官方文档

总体而言，pprint() 是 print() 的轻量级替代，简单实用，非常方便，而且还是 Python 标准库。

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