def is_number(str):
    """
    Checks wether a string is a number or not.
    
    :param str: String.
    :type str: string
    :returns: True if `str` can be converted to a float.
    :rtype: bool
    
    :Example:
    
    >>> is_number('10')
    True
    """
    
    try:
        float(str)
        return True
    except ValueError:
        return False