再也不用Print函数调试啦--神级Python代码调试工具PySnooper的介绍和使用

PySnooper

PySnooper是一款适合菜鸟用的代码调试工具。
如果Python代码哪儿输出不对劲了，之前一般都是利用print函数结合pdb.setTrace()来找问题，如果使用pysnooper的话，那事情就变得简单了！
你可以通过使用这个工具，清楚的看见每一行代码的执行结果以及所有的局部变量的值。只要在函数上添加一个装饰行(类似于装饰器的使用)，就可以打印出该函数每一行执行的结果，支持将结果输出到日志或者命令行。
pysnooper的强大之处在于只需添加decorator就可以，不用加到处加print函数，调试完之后还得一个个删除。那么我们开始吧！
首先安装：

• pip:

pip install pysnooper

• conda with conda-forge channel

conda install -c conda-forge pysnooper

其大致使用方法如下面代码示例

import pysnooper

将函数运行过程写到日志

@pysnooper.snoop("test.log")
def main():
    a = 1
    b = 5
    while a < b:
        a += 1

if __name__ == '__main__':
    main()

将函数运行过程输出到控制台

@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)

Source path:... 
Starting var:.. number = 6
22:17:12.013064 call         2 def number_to_bits(number):
22:17:12.013569 line         3     if number:
22:17:12.013658 line         4         bits = []
New var:....... bits = []
22:17:12.013749 line         5         while number:
22:17:12.013862 line         6             number, remainder = divmod(number, 2)
Modified var:.. number = 3
New var:....... remainder = 0
22:17:12.013948 line         7             bits.insert(0, remainder)
Modified var:.. bits = [0]
22:17:12.014084 line         5         while number:
22:17:12.014198 line         6             number, remainder = divmod(number, 2)
Modified var:.. number = 1
Modified var:.. remainder = 1
22:17:12.014282 line         7             bits.insert(0, remainder)
Modified var:.. bits = [1, 0]
22:17:12.014412 line         5         while number:
22:17:12.014519 line         6             number, remainder = divmod(number, 2)
Modified var:.. number = 0
22:17:12.014669 line         7             bits.insert(0, remainder)
Modified var:.. bits = [1, 1, 0]
22:17:12.014791 line         5         while number:
22:17:12.014900 line         8         return bits
22:17:12.014982 return       8         return bits
Return value:.. [1, 1, 0]





[1, 1, 0]

用with来控制trace的范围，只对with代码块内的代码进行debug信息打印

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()

1 422.0 843



Source path:... 
New var:....... lst = [787, 799, 1, 458, 375, 75, 496, 843, 726, 570]
New var:....... i = 9
22:18:51.357818 line        10         lower = min(lst)
New var:....... lower = 1
22:18:51.358333 line        11         upper = max(lst)
New var:....... upper = 843
22:18:51.358460 line        12         mid = (lower + upper) / 2
New var:....... mid = 422.0
22:18:51.358582 line        13         print(lower, mid, upper)

## 查看某些非局部变量

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

#查看对象的所有属性
@pysnooper.snoop(watch_explode=('foo', 'self'))

##展示我们函数中调用函数的 snoop 行：
@pysnooper.snoop(depth=2)

##将所有用snoop的代码行加前缀，更好找
@pysnooper.snoop(prefix='ZZZ ')

##在多线程下查看实际的线程id
@pysnooper.snoop(thread_info=True)