Python subprocess shell 编程规范

　　使用subprocess通过shell调用另一个模块组件时，需要对返回的code进行判断。判断结果为执行失败时需要raise Exception，不然调用树过于复杂时，我们很难跟踪到异常发生的位置。sys.exit(1)虽然也可以达到对执行结果进行判断的目的，但是它难于追踪异常发生的位置。

 a.py
 `-- b.py
     `-- ls

a.py

 import sys, subprocess

 def exec_cmd(cmd):
     """Run shell command"""
     p = subprocess.Popen(cmd,stdin = subprocess.PIPE, \
         stdout = subprocess.PIPE,
         stderr = subprocess.STDOUT,
         shell = True)

     log_content = p.communicate()[0]

     return p.returncode, log_content

 def main():
     cmd = "python b.py"
     cmd_code, cmd_log = exec_cmd(cmd)
     if not cmd_code == 0:
         raise Exception(cmd_log)

 if __name__ == '__main__':
     main()

b.py

 import sys, subprocess

 def exec_cmd(cmd):
     """Run shell command"""
     p = subprocess.Popen(cmd,stdin = subprocess.PIPE, \
         stdout = subprocess.PIPE,
         stderr = subprocess.STDOUT,
         shell = True)

     log_content = p.communicate()[0]

     return p.returncode, log_content

 def main():
     cmd = """ls c.py"""
     cmd_code, cmd_log = exec_cmd(cmd)
     if not cmd_code == 0:
         raise Exception(cmd_log)

 if __name__ == '__main__':
     main()

运行结果：

 waterforestdeiMac:pythonCrawler waterforest$ python a.py
 Traceback (most recent call last):
   File "a.py", line 21, in <module>
     main()
   File "a.py", line 18, in main
     raise Exception(cmd_log)
 Exception: Traceback (most recent call last):
   File "b.py", line 21, in <module>
     main()
   File "b.py", line 18, in main
     raise Exception(cmd_log)
 Exception: ls: c.py: No such file or directory

 waterforestdeiMac:pythonCrawler waterforest$