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thin abstraction on subprocess.run to simplify admin scripts

Project description

easyproc is a wrapper on the subprocess that provides a similar API, but attempts to reduce some of the boilerplate involved in using the module.

It’s been tested with Python 3.4 and newer, though the timeout feature is broken in 3.4.

It can be installed with pip.

$ pip install easyproc

It provides the Popen class and the run class which function similarly to those in subprocess with a few differences:

  • All streams default to strings (subprocess uses bytes).
  • Error checking is turned on by default. Errors should never pass silently. Unless explicitly silenced.
  • If a string is passed as the initial argument instead of an iterable of arguments, it will be passed to shlex.split automatically.
  • stdout and stderr always behave more or less like files. In some cases, they are special objects. More later.

The module also provides a few convenience

Basics (and Popen)

Ok, now for a few examples.

>>> import easyproc as ep
>>> ep.run('ls -lh')
total 28K
drwxr-xr-x 2 ninjaaron users 4.0K Aug 23  2017 easyproc.egg-info
-rw-r--r-- 1 ninjaaron users  11K Aug 24 09:51 easyproc.py
drwxr-xr-x 2 ninjaaron users 4.0K Aug 24 10:58 __pycache__
-rw-r--r-- 1 ninjaaron users  983 Aug 24 10:56 README.rst
-rw-r--r-- 1 ninjaaron users  491 Mar 26 12:53 setup.py
CompletedProcess(args='ls -lh', returncode=0)
>>> # ^ shlex.split the arguments.
...
>>> ep.run('ls foo')
ls: cannot access 'foo': No such file or directory
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/ninjaaron/src/py/easyproc/easyproc.py", line 207, in run
    retcode = mkchecker(cmd, proc, ok_codes)()
  File "/home/ninjaaron/src/py/easyproc/easyproc.py", line 75, in check_code
    output=proc.stdout, stderr=proc.stderr)
easyproc.CalledProcessError: Command 'ls foo' returned non-zero exit status 2.
Command 'ls foo' returned non-zero exit status 2.
>>> # crash when something doesn't work. You can either handle the
>>> # error or set check=False
...
>>> ep.run('ls foo', check=False)
ls: cannot access 'foo': No such file or directory
CompletedProcess(args='ls foo', returncode=None)
>>>
>>> # normal concurrent stuff with Popen also works. Unicode defaults.
>>> proc = ep.Popen('tr a-z A-Z', stdin=ep.PIPE, stdout=ep.PIPE)
>>> proc.communicate('foo')
('FOO', None)
>>> proc.poll()
0

So all that stuff should look pretty standard from subprocess usage. Aside from the differences mentioned above, easyproc.Popen is more or less identical to subprocess.Popen, so consult the API docs for more info.

Output Streams

As seen above, the run function works similarly to the subprocess equivalent. However, when you capture the output, you don’t get text on the .stdout and .strerr attributes. The proper way to think of Unix command output is not blocks of text, but rather streams of lines, like a text file. (These lines may contain fields, but that isn’t the concern of easyproc).

For this reason, process output is a ProcStream instance. If you use str() on it, you get the string of the process output. However, if you iterate on it, you get lines from the file (with trailing newline removed). It also has a context manager, but you won’t need to access it directly if you use either of those forms patterns.

>>> import easyproc as ep
>>> procstream = ep.run("ls -sh", stdout=ep.PIPE).stdout
>>> # ^ PIPE constant has same usage as in subprocess
...
>>> for line in procstream:
...     print(repr(line))
...
'total 48K'
'4.0K easyproc.egg-info'
' 12K easyproc.py'
' 20K LICENSE'
'4.0K __pycache__'
'4.0K README.rst'
'4.0K setup.py'
>>> # the stream is used up after you iterate on it.
...
>>> procstream = ep.run("ls -sh", stdout=ep.PIPE).stdout
>>> print(procstream)
total 52K
4.0K easyproc.egg-info
 12K easyproc.py
 20K LICENSE
4.0K __pycache__
8.0K README.rst
4.0K setup.py
>>> # print calls str() implicitly.

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