用 pprint 代替 print 更友好的打印调试信息

一时失言乱红尘 2022-11-22 12:52 134阅读 0赞

## 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：

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**

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。

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**

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**

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**

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 ###

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：[https://docs.python.org/zh-cn/3/library/pprint.html][https_docs.python.org_zh-cn_3_library_pprint.html]

简单的说，pprint() 是 print() 的轻量级替代，简单实用，而且它也是 Python 标准库的一员。

[https_docs.python.org_zh-cn_3_library_pprint.html]: https://link.zhihu.com/?target=https%3A//docs.python.org/zh-cn/3/library/pprint.html