在寫算法的時候，總是要每行每個變量一個個的 debug，有時候還要多寫幾個 print，一道算法題要花好長時間才能理解。pysnooper 模塊可以把在運行中變量值都給打印出來。

模塊安裝

1. pip3 install pysnooper

簡單例子

下面是道簡單的力扣算法題作為一個簡單的例子

1. import pysnooper
3. @pysnooper.snoop()
4. def longestCommonPrefix(strs):
5. res = ''
6. for i in zip(*strs):
7. print(i)
8. if len(set(i)) == 1:
9. res += i[0]
10. else
11. break
12. return res
14. if __name__ == 'main':
15. longestCommonPrefix(["flower","flow","flight"])

結(jié)果：

1. 3:38:25.863579 call 4 def longestCommonPrefix(strs):
2. 23:38:25.864474 line 5 res = ''
3. New var:....... res = ''
4. 23:38:25.864474 line 6 for i in zip(*strs):
5. New var:....... i = ('f', 'f', 'f')
6. 23:38:25.865479 line 7 print(i)
7. ('f', 'f', 'f')
8. 23:38:25.866471 line 8 if len(set(i))==1:
9. 23:38:25.866471 line 9 res+=i[0]
10. Modified var:.. res = 'f'
11. 23:38:25.866471 line 6 for i in zip(*strs):
12. Modified var:.. i = ('l', 'l', 'l')
13. 23:38:25.866471 line 7 print(i)
14. ('l', 'l', 'l')
15. 23:38:25.867468 line 8 if len(set(i))==1:
16. 23:38:25.867468 line 9 res+=i[0]
17. Modified var:.. res = 'fl'
18. 23:38:25.868476 line 6 for i in zip(*strs):
19. Modified var:.. i = ('o', 'o', 'i')
20. 23:38:25.868476 line 7 print(i)
21. ('o', 'o', 'i')
22. 23:38:25.869463 line 8 if len(set(i))==1:
23. 23:38:25.869463 line 11 break
24. 23:38:25.869463 line 12 return res
25. 23:38:25.869463 return 12 return res
26. Return value:.. 'fl'
27. Elapsed time: 00:00:00.008201

我們可以看到 pysnooper 把整個執(zhí)行程序都記錄了下來，其中包括行號， 行內(nèi)容，變量的結(jié)果等情況，我們很容易的就看懂了這個算法的真實情況。并且不需要再使用 debug 和 print 調(diào)試代碼。很是省時省力，只需要在方法上面加一行 @pysnooper.snoop()。

復(fù)雜使用

pysnooper 包含了多個參數(shù)，一起來看看吧

output

output 默認(rèn)輸出到控制臺，設(shè)置后輸出到文件，在服務(wù)器中運行的時候，特定的時間出現(xiàn)代碼問題就很容易定位錯誤了，不然容易抓瞎。小編在實際中已經(jīng)被這種問題困擾了好幾次，每次都掉好多頭發(fā)。

1. @pysnooper.snoop('D:\pysnooper.log')
2. def longestCommonPrefix(strs):

示例結(jié)果:

watch 和 watch_explode

watch 用來設(shè)置跟蹤的非局部變量，watch_explode 表示設(shè)置的變量都不監(jiān)控，只監(jiān)控沒設(shè)置的變量，正好和 watch 相反。

1. index = 1
2. @pysnooper.snoop(watch=('index'))
3. def longestCommonPrefix(strs):

示例結(jié)果

沒有加 watch 參數(shù)

1. Starting var:.. strs = ['flower', 'flow', 'flight']
2. 00:12:33.715367 call 5 def longestCommonPrefix(strs):
3. 00:12:33.717324 line 7 res = ''
4. New var:....... res = ''

加了watch 參數(shù)，就會有一個 Starting var:.. index

1. Starting var:.. strs = ['flower', 'flow', 'flight']
2. Starting var:.. index = 1
3. 00:10:35.151036 call 5 def longestCommonPrefix(strs):
4. 00:10:35.151288 line 7 res = ''
5. New var:....... res = ''

depth

depth 監(jiān)控函數(shù)的深度

1. @pysnooper.snoop(depth=2)
2. def longestCommonPrefix(strs):
3. otherMethod()

示例結(jié)果

1. Starting var:.. strs = ['flower', 'flow', 'flight']
2. 00:20:54.059803 call 5 def longestCommonPrefix(strs):
3. 00:20:54.059803 line 6 otherMethod()
4. 00:20:54.060785 call 16 def otherMethod():
5. 00:20:54.060785 line 17 x = 1
6. New var:....... x = 1
7. 00:20:54.060785 line 18 x = x + 1
8. Modified var:.. x = 2
9. 00:20:54.060785 return 18 x = x + 1
10. Return value:.. None
11. 00:20:54.061782 line 7 res = ''

監(jiān)控的結(jié)果顯示，當(dāng)監(jiān)控到調(diào)用的函數(shù)的時候，記錄上會加上縮進，并將它的局部變量和返回值打印處理。

prefix

prefix 輸出內(nèi)容的前綴

1. @pysnooper.snoop(prefix='-------------')
2. def longestCommonPrefix(strs):

示例結(jié)果

1. -------------Starting var:.. strs = ['flower', 'flow', 'flight']
2. -------------00:39:13.986741 call 5 def longestCommonPrefix(strs):
3. -------------00:39:13.987218 line 6 res = ''

relative_time

relative_time 代碼運行的時間

1. @pysnooper.snoop(relative_time=True)
2. def longestCommonPrefix(strs):

示例結(jié)果

1. Starting var:.. strs = ['flower', 'flow', 'flight']
2. 00:00:00.000000 call 5 def longestCommonPrefix(strs):
3. 00:00:00.001998 line 6 res = ''
4. New var:....... res = ''
5. 00:00:00.001998 line 7 for i in zip(*strs):

max_variable_length

max_variable_length 輸出的變量和異常的最大長度，默認(rèn)是 100 個字符，超過 100 個字符就會被截斷，可以設(shè)置為 max_variable_length=None 不截斷輸出

1. @pysnooper.snoop(max_variable_length=5)
2. def longestCommonPrefix(strs):

示例結(jié)果

1. Starting var:.. strs = [...]
2. 00:56:44.343639 call 5 def longestCommonPrefix(strs):
3. 00:56:44.344696 line 6 res = ''
4. New var:....... res = ''
5. 00:56:44.344696 line 7 for i in zip(*strs):
6. New var:....... i = (...)

總結(jié)

本文介紹了怎么使用 pysnooper 工具，pysnooper 不僅可以少一些 debug 和 print，更能幫助理解算法題。

原文鏈接：https://mp.weixin.qq.com/s/rTuxElffIw24GQj_-lAdcw