Random small and useful utilities for python

pyutil.py

'''
A collection of small python snippets that help code looking better
'''

class given(object):
    '''
    make a closure with local variables using with statement

    usage example:

        >>> a=10
        >>> with given(a=5, b=4):
        ...     print(a+b)
        9
        >>> a
        10
        >>> b
        Traceback (most recent call last):
          File "<stdin>", line 1, in <module>
        NameError: name 'b' is not defined

    '''
    def __init__(self, **kwargs_):
        self.vals = kwargs_

    def __enter__(self):
        import inspect
        self.loc = inspect.currentframe().f_back.f_locals
        _lockeys = set(self.loc.keys())
        _vals = set(self.vals.keys())
        self.new_vals = _vals.difference(_lockeys)
        self.backup_vals = {k:self.loc[k] for k in _vals.intersection(_lockeys)}
        self.loc.update(self.vals)

    def __exit__(self, excp_type_, excp_val_, traceback_ ):
        if excp_type_:
            raise excp_type_(excp_val_).with_traceback(traceback_)
        for k in self.new_vals:
            del self.loc[k]
        self.loc.update( self.backup_vals )


class Indexer(object):
    '''
    Creates slices using python's builtin slicing grammar

    To use, call from the singleton instance of this class: idx

    example usage:

        >>> idx[5]
        5
        >>> idx[1,2:3,:-2:2,'key']
        (1, slice(2, 3, None), slice(None, -2, 2), 'key')

    '''
    def __getitem__(self,*args_):
        return args_[0]

idx = Indexer()


class refine(object):
    '''
    Apply a serie of filters, yields successively filtered objects

    Args:
        filters_: iterable of (function->bool | None)

        oil_: iterable elements to be refined

    Yields:
        (idx, elem)

        idx: the number of filter function that first returns True on elem

    Examples:
        TODO
    '''
    def __init__(self, filters_, oil_):
        self.filters = filters_
        self.oil = oil_

    def __iter__(self):
        for elem in self.oil:
            for i,f in enumerate(self.filters):
                if f(elem):
                    yield (i,elem)
                    break


def is2n(n_):
    '''returns whether integer n_ is power of 2'''
    return len(set(bin(n_-1)[2:])) == 1