Function round

numpy/_core/fromnumeric.py:3621–3712

Evenly round to the given number of decimals. Parameters ---------- a : array_like Input data. decimals : int, optional Number of decimal places to round to (default: 0). If decimals is negative, it specifies the number of positions to the left

(a, decimals=0, out=None)

@array_function_dispatch(_round_dispatcher)
def round(a, decimals=0, out=None):
    """
    Evenly round to the given number of decimals.

    Parameters
    ----------
    a : array_like
        Input data.
    decimals : int, optional
        Number of decimal places to round to (default: 0).  If
        decimals is negative, it specifies the number of positions to
        the left of the decimal point.
    out : ndarray, optional
        Alternative output array in which to place the result. It must have
        the same shape as the expected output, but the type of the output
        values will be cast if necessary. See :ref:`ufuncs-output-type`
        for more details.

    Returns
    -------
    rounded_array : ndarray
        An array of the same type as `a`, containing the rounded values.
        Unless `out` was specified, a new array is created.  A reference to
        the result is returned.

        The real and imaginary parts of complex numbers are rounded
        separately.  The result of rounding a float is a float.

    See Also
    --------
    ndarray.round : equivalent method
    around : an alias for this function
    ceil, fix, floor, rint, trunc


    Notes
    -----
    For values exactly halfway between rounded decimal values, NumPy
    rounds to the nearest even value. Thus 1.5 and 2.5 round to 2.0,
    -0.5 and 0.5 round to 0.0, etc.

    ``np.round`` uses a fast but sometimes inexact algorithm to round
    floating-point datatypes. For positive `decimals` it is equivalent to
    ``np.true_divide(np.rint(a * 10**decimals), 10**decimals)``, which has
    error due to the inexact representation of decimal fractions in the IEEE
    floating point standard [1]_ and errors introduced when scaling by powers
    of ten. For instance, note the extra "1" in the following:

        >>> np.round(56294995342131.5, 3)
        56294995342131.51

    If your goal is to print such values with a fixed number of decimals, it is
    preferable to use numpy's float printing routines to limit the number of
    printed decimals:

        >>> np.format_float_positional(56294995342131.5, precision=3)
        '56294995342131.5'