Attempt of a DSL to extract parts from several files

slicer.py

from collections import deque
import io
import re
import sys

__version__ = '0.0.1'

def noop(arg):
    pass

class FilePointer:
    def __init__(self, fp, lineno=1):
        self.fifo = deque()
        self.fp = iter(fp)
        self.lineno = lineno
        
    def __iter__(self):
        return self
    
    def __next__(self):
        if self.fifo:
            line = self.fifo.popleft()
        else:
            line = next(self.fp)
        self.lineno += 1
        return line
    
    def pushback(self, line):
        self.fifo.appendleft(line)
        self.lineno -= 1
        
    def close(self):
        self.fp.close()

class Processor:
    def __init__(self, ofile):
        self.files = {'-': sys.stdin }
        self.src = '-'
        self.output = ofile
        
    def switch(self, filekey):
        if filekey not in self.files:
            if isinstance(filekey, str):
                fp = open(filekey, 'r')
                self.files[filekey] = FilePointer(fp)
            elif hasattr(filekey, 'read'):
                self.files[filekey] = FilePointer(filekey)
            else:
                raise ValueError('Unexpected file key', filekey)
        self.src = filekey
    
    @property
    def _fp(self):
        return self.files[self.src]

    def __enter__(self):
        return self
    
    def __exit__(self, exc_type, exc_value, traceback):
        for k, f in self.files.items():
            if k != '-':
                f.close()

    def _action(self, name, kwargs):
        sgn = [(x, type(y)) for x, y in kwargs.items()]
        if sgn not in [
            [('count', int)],
            [('lineno', int)],
            [('string', str)], 
            [('regex', str)]]:
            raise ValueError('Invalid kwargs for', name, ':', kwargs)
        kw, val = kwargs.popitem()
        send = self.output.write if name == 'take' else noop
        if kw == 'count':
            for i in range(val):
                send(next(self._fp))
        elif kw == 'lineno':
            if self._fp.lineno > val:
                raise ValueError('Already a previous line')
            while self._fp.lineno < val:
                send(next(self._fp))
        elif kw == 'string':
            while True:
                line = next(self._fp)
                if val not in line:
                    send(line)
                else:
                    self._fp.pushback(line)
                    break
        elif kw == 'regex':
            while True:
                line = next(self._fp)
                if not re.search(val, line):
                    send(line)
                else:
                    self._fp.pushback(line)
                    break

    def take(self, **kwargs):
        self._action('take', kwargs)

    def drop(self, **kwargs):
        self._action('drop', kwargs)

def main():
    print("<<<<<<<<<<<<<<<<<RESTART>>>>>>>>>>>>>>>>>>>>")
    a = io.StringIO(TEXT_A)
    b = io.StringIO(TEXT_B)
    with Processor(sys.stdout) as p:
        p.switch(a)
        p.take(count=4)
        p.drop(count=3)
        p.take(count=2)
        p.switch(b)
        p.take(regex=r"each")
        p.take(count=1)
        p.switch(a)
        p.drop(lineno=14)
        p.take(lineno=17)
        p.switch(b)
        p.drop(regex=r"^Till")
        p.take(count=3)
        p.switch(a)
        p.drop(string="et.")
        p.take(regex=r"offi[^\s]{4}")
        p.take(count=1)

TEXT_A = """\
Et sed fuga ullam et nostrum. Quas enim hic harum.
Vel eum est ab ea mollitia. A provident deserunt
necessitatibus nisi totam omnis exercitationem iure.
Recusandae sed enim eius laborum. Alias fugit corrupti
minus quo repellendus iure maxime.

Et totam adipisci incidunt cum deserunt totam. Quia
laudantium non laboriosam accusamus in ut autem laudantium.
Eos exea quibusdam dolorem omnis eaque ex. Voluptate
in inventore architecto cumque.

Neque nostrum nemo inventore. Odit nihil voluptatem
necessitatibus ut consequatur hic sint. Provident
ea fugiat ex libero beatae praesentium. Ea sapiente
perferendis maiores quisquam veniam quibusdam nam.

Voluptatem distinctio ut id reiciendis qui enim
aut. Qui tempora id ut dolor aut voluptatibus et. Vel
dolores dolores eos officiis repudiandae. Similique
fugit totam aut numquam necessitatibus officiis ducimus
alias.

Dicta deleniti veritatis et sapiente nobis et blanditiis iste.
In officiis ea nulla nemo saepe sequi nostrum suscipit. Sit nobis
rerum consequatur non alias quidem.
"""

TEXT_B = """\
The stream is shrunk -- the pool is dry,
And we be comrades, thou and I;
With fevered jowl and dusty flank
Each jostling each along the bank;
And, by one drouthy fear made still,
Forgoing thought of quest or kill.
Now 'neath his dam the fawn may see,
The lean Pack-wolf as cowed as he,
And the tall buck, unflinching, note
The fangs that tore his father's throat.
The pools are shrunk -- the streams are dry,
And we be playmates, thou and I,
Till yonder cloud -- Good Hunting! -- loose
The rain that breaks our Water Truce.
        How Fear Came.

What of the hunting, hunter bold?
Brother, the watch was long and cold.
What of the quarry ye went to kill?
    Brother, he crops in the jungle still.
Where is the power that made your pride?
    Brother, it ebbs from my  flank and side.
Where is the haste that ye hurry by?
    Brother, I go to my lair to die!
        "Tiger-Tiger!"
"""

if __name__ == '__main__':
    main()