无论谁写的程序，必定会存在bug，解决bug需要我们去调试程序。于是乎，在Python中，就会好几种调试手段，如print、assert、logging、pdb、pdb.set_trace()
一、使用print()函数直接打印
>>> def foo(s):... n = int(s)... print(n)... return 10 / n...>>> def main():... foo('0')...>>> main()0Traceback (most recent call last): File " ", line 1, in File " ", line 2, in main File " ", line 4, in fooZeroDivisionError: division by zero 我们可以在认为可能出错的地方打印变量，但这有很大的弊端，因为打印的代码没有实际功能，都是垃圾信息。而且print最后还得删除，所以第二种方法是用assert替代print
二、使用断言assert
>>> def foo(s):... n = int(s)... assert n != 0,'n的值是0!'... return 10 / n...>>> def main():... foo('0')...>>> main()Traceback (most recent call last): File " ", line 1, in File " ", line 2, in main File " ", line 3, in fooAssertionError: n的值是0! assert的意思，当后面的表达式为False时，就会抛出AssertionError，如果为True，什么都不做，直接到下一行。assert有一大特性：在启动python解释器的时候可以使用-O参数来关闭assert（大写的o）
PS E:\Python3.6.3\workspace> python -O err_assert.pyTraceback (most recent call last): File "err_assert.py", line 9, inmain() File "err_assert.py", line 7, in main foo('0') File "err_assert.py", line 4, in foo return 10 / nZeroDivisionError: division by zer
三、使用logging
import logginglogging.basicConfig(level=logging.INFO)s = '0'n = int(s)logging.info('n=%d' % n)print(10/n)#执行结果PS E:\Python3.6.3\workspace> python err_logginginfo.pyINFO:root:n=0Traceback (most recent call last): File "err_logginginfo.py", line 6, in print(10/n)ZeroDivisionError: division by zero 使用logging不会抛出错误，直接输出到文件中。logging可以允许你指定记录信息的级别，级别由低到高分别是debug、info、warning、error、CRITICAL等级别，当定义高级别的时候，低级别的信息不会输出，这是把日志信息输出到控制台console，我们还可以通过设置把日志输出到文件中
四、使用python的调试器pdb
可以让程序以单步方式执行，方便我们随时查看运行状态
新建程序err_pdb.py
s = '0'n = int(s)print(10 / n)
然后以pdb模式启动
PS E:\Python3.6.3\workspace> python -m pdb err_pdb.py> e:\python3.6.3\workspace\err_pdb.py(1)()-> s = '0'(Pdb) l 1 -> s = '0' 2 n = int(s) 3 print(10 / n)[EOF](Pdb) n> e:\python3.6.3\workspace\err_pdb.py(2) ()-> n = int(s)(Pdb) p s'0'(Pdb) p n*** NameError: name 'n' is not defined(Pdb) n> e:\python3.6.3\workspace\err_pdb.py(3) ()-> print(10 / n)(Pdb) p n0(Pdb) p s'0'(Pdb) nZeroDivisionError: division by zero> e:\python3.6.3\workspace\err_pdb.py(3) ()-> print(10 / n)(Pdb) n--Return--> e:\python3.6.3\workspace\err_pdb.py(3) ()->None-> print(10 / n)(Pdb) nZeroDivisionError: division by zero> (1) ()->None(Pdb) n--Return--> (1) ()->None(Pdb) nTraceback (most recent call last): File "E:\Python3.6.3\lib\pdb.py", line 1667, in main pdb._runscript(mainpyfile) File "E:\Python3.6.3\lib\pdb.py", line 1548, in _runscript self.run(statement) File "E:\Python3.6.3\lib\bdb.py", line 431, in run exec(cmd, globals, locals) File " ", line 1, in File "e:\python3.6.3\workspace\err_pdb.py", line 3, in print(10 / n)ZeroDivisionError: division by zeroUncaught exception. Entering post mortem debuggingRunning 'cont' or 'step' will restart the program> e:\python3.6.3\workspace\err_pdb.py(3) ()->None-> print(10 / n)(Pdb) qPost mortem debugger finished. The err_pdb.py will be restarted> e:\python3.6.3\workspace\err_pdb.py(1) ()-> s = '0'(Pdb) n> e:\python3.6.3\workspace\err_pdb.py(2) ()-> n = int(s)(Pdb) qPS E:\Python3.6.3\workspace>
小写字母l，可以列出所有要执行的代码；n 命令表示单步执行代码；p 后面加上变量名，可以随时查看变量的值；在pdb模式中，对于还没有单步执行到的代码，相关的变量的变更是无效的；q 命令退出当前调试，进入重新从头开始调试，再次输入q，就会推出调试程序。这种方式的调试，有一个弊端，就是只能一步一步的执行下去，如果程序有很多行，岂不是累死。
五、使用pdb.set_trace()
#err_pdb.pyimport pdbs = '0'n = int(s)pdb.set_trace() #程序运行到这里会自动停止，等待命令print(10 / n)
我们可以使用l、c、n、p、q等命令来控制和查看程序
PS E:\Python3.6.3\workspace> python err_pdb.py> e:\python3.6.3\workspace\err_pdb.py(7)()-> print(10 / n)(Pdb) p s'0'(Pdb) l 2 import pdb 3 4 s = '0' 5 n = int(s) 6 pdb.set_trace() #程序运行到这里会自动停止，等待命令 7 -> print(10 / n)[EOF](Pdb) nZeroDivisionError: division by zero> e:\python3.6.3\workspace\err_pdb.py(7) ()-> print(10 / n)(Pdb) cTraceback (most recent call last): File "err_pdb.py", line 7, in print(10 / n)ZeroDivisionError: division by zero