Subprocess.Popen() 使用问题解决方案

from subprocess import Popen,PIPE

1.光标处于闪烁等待状态，不能实时输出测试cmd界面.

[原因]：使用communicate()函数，需要等脚本执行完才返回。

def communicate(self, input=None):

    """Interact with process: Send data to stdin.  Read data from stdout and stderr, until end-of-file is reached.  Wait for process to terminate.  
    The optional input argument should be a string to be sent to the child process, or None, if no data should be sent to the child.

    communicate() returns a tuple (stdout, stderr).
    """

[方案]：用subprocess.poll()函数替代, 程序运行完毕后返回1. 否则为None/0.

def poll(self):
    """Check if child process has terminated. Set and return returncode attribute."""
    return self._internal_poll()

2. 输出结果没有换行,一大坨...
[原因]: 未使用
[方案]： 使用while 循环结合readline + poll() 函数, 出来一行打印一行.... stdout.readline() 


Fail 代码：

        p1 = Popen(['bash.exe', 'run_all_tests.sh', 'win32'], stdout=PIPE, shell=True)
        print repr(p1.communicate()[0])  #communicate 函数

 PASS 代码：

#  
1         p1 = Popen(['bash.exe', 'run_all_tests.sh', 'win32'], stdout=subprocess.PIPE, shell=True)
2         while p1.poll() is None:
3             data = p1.stdout.readline()
4             print data
5         #print repr(p1.communicate()[0])

''' # 下面多了层循环，为一个个字符打印 xxx
 3         while p1.poll() is None:
 4             for line in p1.stdout.readline():
 5                 print line
 6         '''

3.传递系统变量env path 的两种方式.

3.1 模仿命令行，windows 用 set 去设置

3.2 [推荐] 不适用set 命令行，直接传递my_env 参数到subpross.Popen()类初始化. 这样可以有效避免字符串转义符号的问题

查看Popen 类帮助文档如下

class Popen(object):
    """ Execute a child program in a new process.

    For a complete description of the arguments see the Python documentation.

    Arguments:
      args: A string, or a sequence of program arguments.

      bufsize: supplied as the buffering argument to the open() function when
          creating the stdin/stdout/stderr pipe file objects

      executable: A replacement program to execute.

      stdin, stdout and stderr: These specify the executed programs' standard
          input, standard output and standard error file handles, respectively.

      preexec_fn: (POSIX only) An object to be called in the child process
          just before the child is executed.

      close_fds: Controls closing or inheriting of file descriptors.

      shell: If true, the command will be executed through the shell.

      cwd: Sets the current directory before the child is executed.

      env: Defines the environment variables for the new process.

      universal_newlines: If true, use universal line endings for file
          objects stdin, stdout and stderr.

      startupinfo and creationflags (Windows only)

    Attributes:
        stdin, stdout, stderr, pid, returncode
    """
    _child_created = False  # Set here since __del__ checks it

    def __init__(self, args, bufsize=0, executable=None,
                 stdin=None, stdout=None, stderr=None,
                 preexec_fn=None, close_fds=False, shell=False,
                 cwd=None, env=None, universal_newlines=False,
                 startupinfo=None, creationflags=0):
        """Create new Popen instance."""

 所以代码加入参数即可：

p1 = Popen(['bash.exe', 'run_all_tests.sh', 'win32'], stdout=PIPE, shell=True, env=my_env)

4. subprocess.call(), Popen() 中shell=False 与shell=True的区别？

如下：但注意这种情况下，此cmd 执行完毕后就关闭. 

所以最好用3.2 的方法设置env.

#默认shell= False时,Fail
subprocess.call(['set', 'CUDA_VISIBLE_DEVICES=%s ', % self.gpuid])

#默认shell=True时,PASS
subprocess.call(['set', 'CUDA_VISIBLE_DEVICES=%s ', % self.gpuid],shell=True)

参考： https://blog.csdn.net/xiaoyaozizai017/article/details/72794469