# Buggy code
def lfilter(b, a, x, axis=-1, zi=None):
    """
    Filter data along one-dimension with an IIR or FIR filter.

    Filter a data sequence, `x`, using a digital filter.  This works for many
    fundamental data types (including Object type).  The filter is a direct
    form II transposed implementation of the standard difference equation
    (see Notes).

    Parameters
    ----------
    b : array_like
        The numerator coefficient vector in a 1-D sequence.
    a : array_like
        The denominator coefficient vector in a 1-D sequence.  If ``a[0]``
        is not 1, then both `a` and `b` are normalized by ``a[0]``.
    x : array_like
        An N-dimensional input array.
    axis : int, optional
        The axis of the input data array along which to apply the
        linear filter. The filter is applied to each subarray along
        this axis.  Default is -1.
    zi : array_like, optional
        Initial conditions for the filter delays.  It is a vector
        (or array of vectors for an N-dimensional input) of length
        ``max(len(a),len(b))-1``.  If `zi` is None or is not given then
        initial rest is assumed.  See `lfiltic` for more information.

    Returns
    -------
    y : array
        The output of the digital filter.
    zf : array, optional
        If `zi` is None, this is not returned, otherwise, `zf` holds the
        final filter delay values.

    Notes
    -----
    The filter function is implemented as a direct II transposed structure.
    This means that the filter implements::

       a[0]*y[n] = b[0]*x[n] + b[1]*x[n-1] + ... + b[nb]*x[n-nb]
                               - a[1]*y[n-1] - ... - a[na]*y[n-na]

    using the following difference equations::

         y[m] = b[0]*x[m] + z[0,m-1]
         z[0,m] = b[1]*x[m] + z[1,m-1] - a[1]*y[m]
         ...
         z[n-3,m] = b[n-2]*x[m] + z[n-2,m-1] - a[n-2]*y[m]
         z[n-2,m] = b[n-1]*x[m] - a[n-1]*y[m]

    where m is the output sample number and n=max(len(a),len(b)) is the
    model order.

    The rational transfer function describing this filter in the
    z-transform domain is::

                             -1               -nb
                 b[0] + b[1]z  + ... + b[nb] z
         Y(z) = ---------------------------------- X(z)
                             -1               -na
                 a[0] + a[1]z  + ... + a[na] z

    """
    a = np.atleast_1d(a)
    if len(a) == 1:
        # This path only supports types fdgFDGO to mirror _linear_filter below.
        # Any of b, a, x, or zi can set the dtype, but there is no default
        # casting of other types; instead a NotImplementedError is raised.
        b = np.asarray(b)
        a = np.asarray(a)
        if b.ndim != 1 and a.ndim != 1:
            raise ValueError("object of too small depth for desired array")
        x = np.asarray(x)
        inputs = [b, a, x]
        if zi is not None:
            # _linear_filter does not broadcast zi, but does do expansion of singleton dims.
            zi = np.asarray(zi)
            if zi.ndim != x.ndim:
                raise ValueError("object of too small depth for desired array")
            expected_shape = list(x.shape)
            expected_shape[axis] = b.shape[0] - 1
            expected_shape = tuple(expected_shape)
            # check the trivial case where zi is the right shape first
            if zi.shape != expected_shape:
                strides = zi.ndim * [None]
                if axis < 0:
                    axis += zi.ndim
                for k in range(zi.ndim):
                    if k == axis and zi.shape[k] == expected_shape[k]:
                        strides[k] = zi.strides[k]
                    elif k != axis and zi.shape[k] == expected_shape[k]:
                        strides[k] = zi.strides[k]
                    elif k != axis and zi.shape[k] == 1:
                        strides[k] = 0
                    else:
                        raise ValueError(
                            "Unexpected shape for zi: expected "
                            "%s, found %s." % (expected_shape, zi.shape)
                        )
                zi = np.lib.stride_tricks.as_strided(zi, expected_shape, strides)
            inputs.append(zi)
        dtype = np.result_type(*inputs)

        if dtype.char not in "fdgFDGO":
            raise NotImplementedError("input type '%s' not supported" % dtype)

        b = np.array(b, dtype=dtype)
        a = np.array(a, dtype=dtype, copy=False)
        b /= a[0]
        x = np.array(x, dtype=dtype, copy=False)

        out_full = np.apply_along_axis(lambda y: np.convolve(b, y), axis, x)
        ind = out_full.ndim * [slice(None)]
        ind[axis] = slice(out_full.shape[axis] - len(b) + 1)
        out = out_full[ind]
        if zi is None:
            return out
        else:
            ind[axis] = slice(out_full.shape[axis] - len(b) + 1, None)
            zf = out_full[ind]
            ind[axis] = slice(zi.shape[axis])
            out[ind] += zi
            return out, zf
    else:
        if zi is None:
            return sigtools._linear_filter(b, a, x, axis)
        else:
            return sigtools._linear_filter(b, a, x, axis, zi)


# Traceback (ValueError)
Traceback (most recent call last):
File "filter_debug2.py", line 14, in <module>
result = filter_sbs()
File "filter_debug2.py", line 10, in filter_sbs
result[i], z = signal.lfilter(b, 1, [x], zi=z)
File "/usr/local/lib/python3.4/dist-packages/scipy/signal/signaltools.py", line 956, in lfilter
out[ind] += zi
ValueError: non-broadcastable output operand with shape (1,) doesn't match the broadcast shape (149,)

# Fixed code
def lfilter(b, a, x, axis=-1, zi=None):
    """
    Filter data along one-dimension with an IIR or FIR filter.

    Filter a data sequence, `x`, using a digital filter.  This works for many
    fundamental data types (including Object type).  The filter is a direct
    form II transposed implementation of the standard difference equation
    (see Notes).

    Parameters
    ----------
    b : array_like
        The numerator coefficient vector in a 1-D sequence.
    a : array_like
        The denominator coefficient vector in a 1-D sequence.  If ``a[0]``
        is not 1, then both `a` and `b` are normalized by ``a[0]``.
    x : array_like
        An N-dimensional input array.
    axis : int, optional
        The axis of the input data array along which to apply the
        linear filter. The filter is applied to each subarray along
        this axis.  Default is -1.
    zi : array_like, optional
        Initial conditions for the filter delays.  It is a vector
        (or array of vectors for an N-dimensional input) of length
        ``max(len(a),len(b))-1``.  If `zi` is None or is not given then
        initial rest is assumed.  See `lfiltic` for more information.

    Returns
    -------
    y : array
        The output of the digital filter.
    zf : array, optional
        If `zi` is None, this is not returned, otherwise, `zf` holds the
        final filter delay values.

    Notes
    -----
    The filter function is implemented as a direct II transposed structure.
    This means that the filter implements::

       a[0]*y[n] = b[0]*x[n] + b[1]*x[n-1] + ... + b[nb]*x[n-nb]
                               - a[1]*y[n-1] - ... - a[na]*y[n-na]

    using the following difference equations::

         y[m] = b[0]*x[m] + z[0,m-1]
         z[0,m] = b[1]*x[m] + z[1,m-1] - a[1]*y[m]
         ...
         z[n-3,m] = b[n-2]*x[m] + z[n-2,m-1] - a[n-2]*y[m]
         z[n-2,m] = b[n-1]*x[m] - a[n-1]*y[m]

    where m is the output sample number and n=max(len(a),len(b)) is the
    model order.

    The rational transfer function describing this filter in the
    z-transform domain is::

                             -1               -nb
                 b[0] + b[1]z  + ... + b[nb] z
         Y(z) = ---------------------------------- X(z)
                             -1               -na
                 a[0] + a[1]z  + ... + a[na] z

    """
    a = np.atleast_1d(a)
    if len(a) == 1:
        # This path only supports types fdgFDGO to mirror _linear_filter below.
        # Any of b, a, x, or zi can set the dtype, but there is no default
        # casting of other types; instead a NotImplementedError is raised.
        b = np.asarray(b)
        a = np.asarray(a)
        if b.ndim != 1 and a.ndim != 1:
            raise ValueError("object of too small depth for desired array")
        x = np.asarray(x)
        inputs = [b, a, x]
        if zi is not None:
            # _linear_filter does not broadcast zi, but does do expansion of singleton dims.
            zi = np.asarray(zi)
            if zi.ndim != x.ndim:
                raise ValueError("object of too small depth for desired array")
            expected_shape = list(x.shape)
            expected_shape[axis] = b.shape[0] - 1
            expected_shape = tuple(expected_shape)
            # check the trivial case where zi is the right shape first
            if zi.shape != expected_shape:
                strides = zi.ndim * [None]
                if axis < 0:
                    axis += zi.ndim
                for k in range(zi.ndim):
                    if k == axis and zi.shape[k] == expected_shape[k]:
                        strides[k] = zi.strides[k]
                    elif k != axis and zi.shape[k] == expected_shape[k]:
                        strides[k] = zi.strides[k]
                    elif k != axis and zi.shape[k] == 1:
                        strides[k] = 0
                    else:
                        raise ValueError(
                            "Unexpected shape for zi: expected "
                            "%s, found %s." % (expected_shape, zi.shape)
                        )
                zi = np.lib.stride_tricks.as_strided(zi, expected_shape, strides)
            inputs.append(zi)
        dtype = np.result_type(*inputs)

        if dtype.char not in "fdgFDGO":
            raise NotImplementedError("input type '%s' not supported" % dtype)

        b = np.array(b, dtype=dtype)
        a = np.array(a, dtype=dtype, copy=False)
        b /= a[0]
        x = np.array(x, dtype=dtype, copy=False)

        out_full = np.apply_along_axis(lambda y: np.convolve(b, y), axis, x)
        ind = out_full.ndim * [slice(None)]
        if zi is not None:
            ind[axis] = slice(zi.shape[axis])
            out_full[ind] += zi

        ind[axis] = slice(out_full.shape[axis] - len(b) + 1)
        out = out_full[ind]

        if zi is None:
            return out
        else:
            ind[axis] = slice(out_full.shape[axis] - len(b) + 1, None)
            zf = out_full[ind]
            return out, zf
    else:
        if zi is None:
            return sigtools._linear_filter(b, a, x, axis)
        else:
            return sigtools._linear_filter(b, a, x, axis, zi)