Source code for osrf_pycommon.process_utils.impl

# Copyright 2014 Open Source Robotics Foundation, Inc.
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# See the License for the specific language governing permissions and
# limitations under the License.

import os
import sys

from .execute_process_nopty import _execute_process_nopty
    from .execute_process_pty import _execute_process_pty
except ImportError:
    # pty doesn't work on Windows, it will fail to import
    # so fallback to non pty implementation
    _execute_process_pty = None

    _basestring = basestring  # Python 2
except NameError:
    _basestring = str  # Python 3

[docs]def execute_process(cmd, cwd=None, env=None, shell=False, emulate_tty=False): """Executes a command with arguments and returns output line by line. All arguments, except ``emulate_tty``, are passed directly to :py:class:`subprocess.Popen`. ``execute_process`` returns a generator which yields the output, line by line, until the subprocess finishes at which point the return code is yielded. This is an example of how this function should be used: .. code-block:: python from __future__ import print_function from osrf_pycommon.process_utils import execute_process cmd = ['ls', '-G'] for line in execute_process(cmd, cwd='/usr'): if isinstance(line, int): # This is a return code, the command has exited print("'{0}' exited with: {1}".format(' '.join(cmd), line)) continue # break would also be appropriate here # In Python 3, it will be a bytes array which needs to be decoded if not isinstance(line, str): line = line.decode('utf-8') # Then print it to the screen print(line, end='') ``stdout`` and ``stderr`` are always captured together and returned line by line through the returned generator. New line characters are preserved in the output, so if re-printing the data take care to use ``end=''`` or first ``rstrip`` the output lines. When ``emulate_tty`` is used on Unix systems, commands will identify that they are on a tty and should output color to the screen as if you were running it on the terminal, and therefore there should not be any need to pass arguments like ``-c color.ui=always`` to commands like ``git``. Additionally, programs might also behave differently in when ``emulate_tty`` is being used, for example, Python will default to unbuffered output when it detects a tty. ``emulate_tty`` works by using psuedo-terminals on Unix machines, and so if you are running this command many times in parallel (like hundreds of times) then you may get one of a few different :py:exc:`OSError`'s. For example, "OSError: [Errno 24] Too many open files: '/dev/ttyp0'" or "OSError: out of pty devices". You should also be aware that you share pty devices with the rest of the system, so even if you are not using a lot, it is possible to get this error. You can catch this error before getting data from the generator, so when using ``emulate_tty`` you might want to do something like this: .. code-block:: python from __future__ import print_function from osrf_pycommon.process_utils import execute_process cmd = ['ls', '-G', '/usr'] try: output = execute_process(cmd, emulate_tty=True) except OSError: output = execute_process(cmd, emulate_tty=False) for line in output: if isinstance(line, int): print("'{0}' exited with: {1}".format(' '.join(cmd), line)) continue # In Python 3, it will be a bytes array which needs to be decoded if not isinstance(line, str): line = line.decode('utf-8') print(line, end='') This way if a pty cannot be opened in order to emulate the tty then you can try again without emulation, and any other :py:exc:`OSError` should raise again with ``emulate_tty`` set to ``False``. Obviously, you only want to do this if emulating the tty is non-critical to your processing, like when you are using it to capture color. Any color information that the command outputs as ANSI escape sequences is captured by this command. That way you can print the output to the screen and preserve the color formatting. If you do not want color to be in the output, then try setting ``emulate_tty`` to ``False``, but that does not guarantee that there is no color in the output, instead it only will cause called processes to identify that they are not being run in a terminal. Most well behaved programs will not output color if they detect that they are not being executed in a terminal, but you shouldn't rely on that. If you want to ensure there is no color in the output from an executed process, then use this function: :py:func:`osrf_pycommon.terminal_color.remove_ansi_escape_senquences` Exceptions can be raised by functions called by the implementation, for example, :py:class:`subprocess.Popen` can raise an :py:exc:`OSError` when the given command is not found. If you want to check for the existence of an executable on the path, see: :py:func:`which`. However, this function itself does not raise any special exceptions. :param list cmd: list of strings with the first item being a command and subsequent items being any arguments to that command; passed directly to :py:class:`subprocess.Popen`. :param str cwd: path in which to run the command, defaults to None which means :py:func:`os.getcwd` is used; passed directly to :py:class:`subprocess.Popen`. :param dict env: environment dictionary to use for executing the command, default is None which uses the :py:obj:`os.environ` environment; passed directly to :py:class:`subprocess.Popen`. :param bool shell: If True the system shell is used to evaluate the command, default is False; passed directly to :py:class:`subprocess.Popen`. :param bool emulate_tty: If True attempts to use a pty to convince subprocess's that they are being run in a terminal. Typically this is useful for capturing colorized output from commands. This does not work on Windows (no pty's), so it is considered False even when True. Defaults to False. :returns: a generator which yields output from the command line by line :rtype: generator which yields strings """ exp_func = _execute_process_nopty if emulate_tty and _execute_process_pty is not None: exp_func = _execute_process_pty for out, err, ret in exp_func(cmd, cwd, env, shell, stderr_to_stdout=True): if ret is None: yield out continue yield ret
[docs]def execute_process_split( cmd, cwd=None, env=None, shell=False, emulate_tty=False ): """:py:func:`execute_process`, except ``stderr`` is returned separately. Instead of yielding output line by line until yielding a return code, this function always a triplet of ``stdout``, ``stderr``, and return code. Each time only one of the three will not be None. Once you receive a non-None return code (type will be int) there will be no more ``stdout`` or ``stderr``. Therefore you can use the command like this: .. code-block:: python from __future__ import print_function import sys from osrf_pycommon.process_utils import execute_process_split cmd = ['time', 'ls', '-G'] for out, err, ret in execute_process_split(cmd, cwd='/usr'): # In Python 3, it will be a bytes array which needs to be decoded out = out.decode('utf-8') if out is not None else None err = err.decode('utf-8') if err is not None else None if ret is not None: # This is a return code, the command has exited print("'{0}' exited with: {1}".format(' '.join(cmd), ret)) break if out is not None: print(out, end='') if err is not None: print(err, end='', file=sys.stderr) When using this, it is possible that the ``stdout`` and ``stderr`` data can be returned in a different order than what would happen on the terminal. This is due to the fact that the subprocess is given different buffers for ``stdout`` and ``stderr`` and so there is a race condition on the subprocess writing to the different buffers and this command reading the buffers. This can be avoided in most scenarios by using ``emulate_tty``, because of the use of ``pty``'s, though the ordering can still not be guaranteed and the number of ``pty``'s is finite as explained in the documentation for :py:func:`execute_process`. For situations where output ordering between ``stdout`` and ``stderr`` are critical, they should not be returned separately and instead should share one buffer, and so :py:func:`execute_process` should be used. For all other parameters and documentation see: :py:func:`execute_process` """ exp_func = _execute_process_nopty if emulate_tty and _execute_process_pty is not None: exp_func = _execute_process_pty return exp_func(cmd, cwd, env, shell, stderr_to_stdout=False)
try: from shutil import which as _which except ImportError: _which = None def _which_backport(cmd, mode=os.F_OK | os.X_OK, path=None): # Check that a given file can be accessed with the correct mode. # Additionally check that `file` is not a directory, as on Windows # directories pass the os.access check. def _access_check(fn, mode): return (os.path.exists(fn) and os.access(fn, mode) and not os.path.isdir(fn)) # If we're given a path with a directory part, look it up directly rather # than referring to PATH directories. This includes checking relative # to the current directory, e.g. ./script if os.path.dirname(cmd): if _access_check(cmd, mode): return cmd return None if path is None: path = os.environ.get("PATH", os.defpath) if not path: return None path = path.split(os.pathsep) if sys.platform == "win32": # The current directory takes precedence on Windows. if os.curdir not in path: path.insert(0, os.curdir) # PATHEXT is necessary to check on Windows. pathext = os.environ.get("PATHEXT", "").split(os.pathsep) # See if the given file matches any of the expected path extensions. # This will allow us to short circuit when given "python.exe". # If it does match, only test that one, otherwise we have to try # others. if any(cmd.lower().endswith(ext.lower()) for ext in pathext): files = [cmd] else: files = [cmd + ext for ext in pathext] else: # On other platforms you don't have things like PATHEXT to tell you # what file suffixes are executable, so just pass on cmd as-is. files = [cmd] seen = set() for directory in path: normdir = os.path.normcase(directory) if normdir not in seen: seen.add(normdir) for thefile in files: name = os.path.join(directory, thefile) if _access_check(name, mode): return name return None
[docs]def which(cmd, mode=os.F_OK | os.X_OK, path=None, **kwargs): """Given a command, mode, and a PATH string, return the path which conforms to the given mode on the PATH, or None if there is no such file. `mode` defaults to ``os.F_OK | os.X_OK``. `path` defaults to the result of ``os.environ.get("PATH")``, or can be overridden with a custom search path. Backported from :py:func:`shutil.which` (`<>`_), available in Python 3.3. """ kwargs.update({'mode': mode, 'path': path}) global _which if _which is not None: return _which(cmd, **kwargs) return _which_backport(cmd, **kwargs)