PySnooper：非常好用的python代码调试帮助工具！

PySnooper是一个给平民用的调试器，因为它是完全免费的！使用pysnooper可以完整的输出函数每一行代码中的变量的值，供我们去观察。github网址：PySnooper - Never use print for debugging again

1.示例

下面这个函数的功能是，通过返回一个位列表将数字转换为二进制。然后通过添加@pysnooper.snoop() 装饰器来追踪它的每一行的变量的值：

import pysnooper

@pysnooper.snoop()
def number_to_bits(number):
    if number:
        bits = []
        while number:
            number, remainder = divmod(number, 2)
            bits.insert(0, remainder)
        return bits
    else:
        return [0]

number_to_bits(6)

stderr的输出是：

Starting var:.. number = 6
15:29:11.327032 call         4 def number_to_bits(number):
15:29:11.327032 line         5     if number:
15:29:11.327032 line         6         bits = []
New var:....... bits = []
15:29:11.327032 line         7         while number:
15:29:11.327032 line         8             number, remainder = divmod(number, 2)
New var:....... remainder = 0
Modified var:.. number = 3
15:29:11.327032 line         9             bits.insert(0, remainder)
Modified var:.. bits = [0]
15:29:11.327032 line         7         while number:
15:29:11.327032 line         8             number, remainder = divmod(number, 2)
Modified var:.. number = 1
Modified var:.. remainder = 1
15:29:11.327032 line         9             bits.insert(0, remainder)
Modified var:.. bits = [1, 0]
15:29:11.327032 line         7         while number:
15:29:11.327032 line         8             number, remainder = divmod(number, 2)
Modified var:.. number = 0
15:29:11.327032 line         9             bits.insert(0, remainder)
Modified var:.. bits = [1, 1, 0]
15:29:11.327032 line         7         while number:
15:29:11.327032 line        10         return bits
15:29:11.327032 return      10         return bits
Return value:.. [1, 1, 0]

2.指定输出内容：

如果不想跟踪整个函数，可以将自己想要跟踪的内容编写在with块中，如下所示，输出lst列表中的最大值、最小值和中间值：

import pysnooper
import random

def foo():
    lst = []
    for i in range(10):
        lst.append(random.randrange(1, 1000))

    with pysnooper.snoop():
        lower = min(lst)
        upper = max(lst)
        mid = (lower + upper) / 2
        print(lower, mid, upper)

foo()

输出如下：

New var:....... lst = [871, 383, 481, 214, 863, 362, 405, 452, 36, 325]
New var:....... i = 9
New var:....... lst = [681, 267, 74, 832, 284, 678, ...]
09:37:35.881721 line        10         lower = min(lst)
New var:....... lower = 74
09:37:35.882137 line        11         upper = max(lst)
New var:....... upper = 832
09:37:35.882304 line        12         mid = (lower + upper) / 2
74 453.0 832
New var:....... mid = 453.0
09:37:35.882486 line        13         print(lower, mid, upper)
36 453.5 871

3.如果跟踪内容太长，可以将其输出到本地日志文件中

@pysnooper.snoop('/path/to/logfile/file.log')

4.查看一些非局部变量的表达式的值

@pysnooper.snoop(watch=('foo.bar', 'self.x["whatever"]'))

或者查看非局部变量的所有属性列表：

@pysnooper.snoop(watch_explode=('foo', 'self'))

5.跟踪函数中调用的函数

使用depth来设置跟踪的函数调用深度：

@pysnooper.snoop(depth=2)

6.设置一个前缀名，将更容易定位和找到snoop行

@pysnooper.snoop(prefix='ZZZ ')

7.在多线程应用程序上识别哪个线程在输出中被跟踪

@pysnooper.snoop(thread_info=True)

这一项没看懂，有懂的大神，帮忙留言解释一下！

PySnooper：非常好用的python代码调试帮助工具！

相关推荐