How to create fabric2 tasks decorators?

Question

Let's start by considering some unrefactored working piece of code that uses fabric2:

import traceback import inspect


from fabric2.tasks import task 
from fabric2 import Config, Connection


def get_function_name():
    return traceback.extract_stack(None, 2)[0][2]


def get_function_parameters_and_values():
    frame = inspect.currentframe().f_back
    args, _, _, values = inspect.getargvalues(frame)
    return ", ".join([str(i) for i in args])


@task def foo1(c, arg1):
    print(f'<{get_function_name()} {get_function_parameters_and_values()}>')

    def _inner():
        if int(arg1) < 5:
            print('arg1 is not big enough')
            return
        print('doing foo1 stuff')
    res = _inner()
    print(f'</{get_function_name}')
    return res


@task def foo2(c, arg1, arg2):
    print(f'<{get_function_name()} {get_function_parameters_and_values()}>')

    def _inner():
        if int(arg1) < 5 and int(arg2) < 5:
            print('arg1 & arg2 are not big enough')
            return
        print('doing foo2 stuff')
    res = _inner()
    print(f'</{get_function_name}')
    return res

Now, as you can see above, there is some code duplication I'd like to factor out in the way of a wrapper/decorator... Problem comes if I try something like this:

def wrap(func):
    def wrapped(*args, **kwargs):
        print('begin')
        res = func(*args, **kwargs)
        print('end')
    return wrapped


@task
@wrap
def foo3(c, arg1):
    if int(arg1) < 5:
        print('arg1 is not big enough')
        return
    print('doing foo3 stuff')


@wrap
@task
def foo4(c, arg1):
    if int(arg1) < 5:
        print('arg1 is not big enough')
        return
    print('doing foo4 stuff')

And I run either of these tasks I'll get exceptions with both such as:

(py364_32) D:\sources\personal\python\bplfab\examples>fab2 foo3 --arg1=3
Traceback (most recent call last):
  File "d:\virtual_envs\py364_32\lib\site-packages\invoke\tasks.py", line 160, in argspec
    context_arg = arg_names.pop(0)
IndexError: pop from empty list

During handling of the above exception, another exception occurred:

    Traceback (most recent call last):
      File "d:\software\python364_32\Lib\runpy.py", line 193, in _run_module_as_main
        "__main__", mod_spec)
      File "d:\software\python364_32\Lib\runpy.py", line 85, in _run_code
        exec(code, run_globals)
      File "D:\virtual_envs\py364_32\Scripts\fab2.exe\__main__.py", line 7, in <module>
      File "d:\virtual_envs\py364_32\lib\site-packages\invoke\program.py", line 352, in run
        self.parse_collection()
      File "d:\virtual_envs\py364_32\lib\site-packages\invoke\program.py", line 444, in parse_collection
        self.load_collection()
      File "d:\virtual_envs\py364_32\lib\site-packages\fabric2\main.py", line 87, in load_collection
        super(Fab, self).load_collection()
      File "d:\virtual_envs\py364_32\lib\site-packages\invoke\program.py", line 661, in load_collection
        module, parent = loader.load(coll_name)
      File "d:\virtual_envs\py364_32\lib\site-packages\invoke\loader.py", line 76, in load
        module = imp.load_module(name, fd, path, desc)
      File "d:\virtual_envs\py364_32\lib\imp.py", line 235, in load_module
        return load_source(name, filename, file)
      File "d:\virtual_envs\py364_32\lib\imp.py", line 172, in load_source
        module = _load(spec)
      File "<frozen importlib._bootstrap>", line 684, in _load
      File "<frozen importlib._bootstrap>", line 665, in _load_unlocked
      File "<frozen importlib._bootstrap_external>", line 678, in exec_module
      File "<frozen importlib._bootstrap>", line 219, in _call_with_frames_removed
      File "D:\sources\personal\python\bplfab\examples\fabfile.py", line 59, in <module>
        @wrap
      File "d:\virtual_envs\py364_32\lib\site-packages\fabric2\tasks.py", line 71, in task
        return invoke.task(*args, **kwargs)
      File "d:\virtual_envs\py364_32\lib\site-packages\invoke\tasks.py", line 313, in task
        return klass(args[0], **kwargs)
      File "d:\virtual_envs\py364_32\lib\site-packages\fabric2\tasks.py", line 21, in __init__
        super(Task, self).__init__(*args, **kwargs)
      File "d:\virtual_envs\py364_32\lib\site-packages\invoke\tasks.py", line 77, in __init__
        self.positional = self.fill_implicit_positionals(positional)
      File "d:\virtual_envs\py364_32\lib\site-packages\invoke\tasks.py", line 168, in fill_implicit_positionals
        args, spec_dict = self.argspec(self.body)
      File "d:\virtual_envs\py364_32\lib\site-packages\invoke\tasks.py", line 163, in argspec
        raise TypeError("Tasks must have an initial Context argument!")
    TypeError: Tasks must have an initial Context argument!

    (py364_32) D:\sources\personal\python\bplfab\examples>fab2 foo4 --arg1=3
    Traceback (most recent call last):
      File "d:\virtual_envs\py364_32\lib\site-packages\invoke\tasks.py", line 160, in argspec
        context_arg = arg_names.pop(0)
    IndexError: pop from empty list

    During handling of the above exception, another exception occurred:

    Traceback (most recent call last):
      File "d:\software\python364_32\Lib\runpy.py", line 193, in _run_module_as_main
        "__main__", mod_spec)
      File "d:\software\python364_32\Lib\runpy.py", line 85, in _run_code
        exec(code, run_globals)
      File "D:\virtual_envs\py364_32\Scripts\fab2.exe\__main__.py", line 7, in <module>
      File "d:\virtual_envs\py364_32\lib\site-packages\invoke\program.py", line 352, in run
        self.parse_collection()
      File "d:\virtual_envs\py364_32\lib\site-packages\invoke\program.py", line 444, in parse_collection
        self.load_collection()
      File "d:\virtual_envs\py364_32\lib\site-packages\fabric2\main.py", line 87, in load_collection
        super(Fab, self).load_collection()
      File "d:\virtual_envs\py364_32\lib\site-packages\invoke\program.py", line 661, in load_collection
        module, parent = loader.load(coll_name)
      File "d:\virtual_envs\py364_32\lib\site-packages\invoke\loader.py", line 76, in load
        module = imp.load_module(name, fd, path, desc)
      File "d:\virtual_envs\py364_32\lib\imp.py", line 235, in load_module
        return load_source(name, filename, file)
      File "d:\virtual_envs\py364_32\lib\imp.py", line 172, in load_source
        module = _load(spec)
      File "<frozen importlib._bootstrap>", line 684, in _load
      File "<frozen importlib._bootstrap>", line 665, in _load_unlocked
      File "<frozen importlib._bootstrap_external>", line 678, in exec_module
      File "<frozen importlib._bootstrap>", line 219, in _call_with_frames_removed
      File "D:\sources\personal\python\bplfab\examples\fabfile.py", line 59, in <module>
        @wrap
      File "d:\virtual_envs\py364_32\lib\site-packages\fabric2\tasks.py", line 71, in task
        return invoke.task(*args, **kwargs)
      File "d:\virtual_envs\py364_32\lib\site-packages\invoke\tasks.py", line 313, in task
        return klass(args[0], **kwargs)
      File "d:\virtual_envs\py364_32\lib\site-packages\fabric2\tasks.py", line 21, in __init__
        super(Task, self).__init__(*args, **kwargs)
      File "d:\virtual_envs\py364_32\lib\site-packages\invoke\tasks.py", line 77, in __init__
        self.positional = self.fill_implicit_positionals(positional)
      File "d:\virtual_envs\py364_32\lib\site-packages\invoke\tasks.py", line 168, in fill_implicit_positionals
        args, spec_dict = self.argspec(self.body)
      File "d:\virtual_envs\py364_32\lib\site-packages\invoke\tasks.py", line 163, in argspec
        raise TypeError("Tasks must have an initial Context argument!")
    TypeError: Tasks must have an initial Context argument!

It seems there is already an opened issue related somehow to this https://github.com/pyinvoke/invoke/issues/555 but so far I haven't been able to find a workaround for this.

Could you explain me what I'm doing wrong here? But the most important, could you provide a way to workaround this fabric2 "limitation" and being able to create a decorator that allows me to use inspect to capture the task's name as well as the arguments passed in the command line?

Thanks in advance.

why don't you put duplicated code in separated function and run it as normal function. — furas, Jan 03 '20 at 15:06
you can get fabric2's source code and see how they created decorator `task`. You could find source code using `print(fabric2.__file__)` — furas, Jan 03 '20 at 15:11

score 1 · Answer 1 · answered Oct 24 '20 at 21:16

Custom decorators must have a fixed initial context argument as the exception says, so func(c, *args, **kwargs) works while func(*args, **kwargs) doesn't:

def trace(func):
    @functools.wraps(func)
    def wrapper(c, *args, **kwargs):
        print(f'Begin {func.__name__}')
        func(c, *args, **kwargs)
        print(f'End {func.__name__}')
    return wrapper

@task
@trace
def uname(c):
    c.run('uname -a')

How to create fabric2 tasks decorators?

1 Answers1