to_unit.py

import re
 
def to_units(value, unit):
    """
    Convert a size string from unit x to unit y.
        
    Input:
        value (str): Size string
        unit  (str): Unit to convert to
    Output:
        r_value (str): Size string
    """
    units = [ 'B', 'K', 'M', 'G', 'T', 'P', 'E' ]
    
    # Confirm provided unit is supported
    unit = unit.upper()
    if unit not in units:
        raise ValueError('invalid unit %s' % unit)
 
    # Match any floating point number followed by an optional unit
    m = re.search(r'^([0-9]*\.?[0-9]+)([%s])?b?$' % ''.join(units), value, re.IGNORECASE)
    if not m:
        raise ValueError('invalid format %s' % value)
    v_num = float(m.group(1))
    if m.group(2):
        v_unit = m.group(2).upper()
    else:
        v_unit = 'B'
    
    # Perform byte calculation
    v_byte = v_num * 1024 ** units.index(v_unit)
    
    # Perform byte to string conversion
    r_num = v_byte / 1024 ** units.index(unit)
    r_value = '%s%sB' % ("{0:.2f}".format(r_num), unit)
    
    return r_value