下面是一个使用while的选项:

def number_format(n):
   n2, n3 = n, 0
   while n2 >= 1e3:
      n2 /= 1e3
      n3 += 1
   return '%.3f' % n2 + ('', ' k', ' M', ' G')[n3]

s = number_format(9012345678)
print(s == '9.012 G')

https://docs.python.org/reference/compound_stmts.html#while

参考Sridhar Ratnakumar的回答，更新为:

def formatSize(sizeInBytes, decimalNum=1, isUnitWithI=False, sizeUnitSeperator=""):
  """format size to human readable string"""
  # https://en.wikipedia.org/wiki/Binary_prefix#Specific_units_of_IEC_60027-2_A.2_and_ISO.2FIEC_80000
  # K=kilo, M=mega, G=giga, T=tera, P=peta, E=exa, Z=zetta, Y=yotta
  sizeUnitList = ['','K','M','G','T','P','E','Z']
  largestUnit = 'Y'

  if isUnitWithI:
    sizeUnitListWithI = []
    for curIdx, eachUnit in enumerate(sizeUnitList):
      unitWithI = eachUnit
      if curIdx >= 1:
        unitWithI += 'i'
      sizeUnitListWithI.append(unitWithI)

    # sizeUnitListWithI = ['','Ki','Mi','Gi','Ti','Pi','Ei','Zi']
    sizeUnitList = sizeUnitListWithI

    largestUnit += 'i'

  suffix = "B"
  decimalFormat = "." + str(decimalNum) + "f" # ".1f"
  finalFormat = "%" + decimalFormat + sizeUnitSeperator + "%s%s" # "%.1f%s%s"
  sizeNum = sizeInBytes
  for sizeUnit in sizeUnitList:
      if abs(sizeNum) < 1024.0:
        return finalFormat % (sizeNum, sizeUnit, suffix)
      sizeNum /= 1024.0
  return finalFormat % (sizeNum, largestUnit, suffix)

示例输出如下:

def testKb():
  kbSize = 3746
  kbStr = formatSize(kbSize)
  print("%s -> %s" % (kbSize, kbStr))

def testI():
  iSize = 87533
  iStr = formatSize(iSize, isUnitWithI=True)
  print("%s -> %s" % (iSize, iStr))

def testSeparator():
  seperatorSize = 98654
  seperatorStr = formatSize(seperatorSize, sizeUnitSeperator=" ")
  print("%s -> %s" % (seperatorSize, seperatorStr))

def testBytes():
  bytesSize = 352
  bytesStr = formatSize(bytesSize)
  print("%s -> %s" % (bytesSize, bytesStr))

def testMb():
  mbSize = 76383285
  mbStr = formatSize(mbSize, decimalNum=2)
  print("%s -> %s" % (mbSize, mbStr))

def testTb():
  tbSize = 763832854988542
  tbStr = formatSize(tbSize, decimalNum=2)
  print("%s -> %s" % (tbSize, tbStr))

def testPb():
  pbSize = 763832854988542665
  pbStr = formatSize(pbSize, decimalNum=4)
  print("%s -> %s" % (pbSize, pbStr))


def demoFormatSize():
  testKb()
  testI()
  testSeparator()
  testBytes()
  testMb()
  testTb()
  testPb()

  # 3746 -> 3.7KB
  # 87533 -> 85.5KiB
  # 98654 -> 96.3 KB
  # 352 -> 352.0B
  # 76383285 -> 72.84MB
  # 763832854988542 -> 694.70TB
  # 763832854988542665 -> 678.4199PB

现代Django有自模板标签filesizeformat:

将值格式化为人类可读的文件大小(即:“13 KB”，“4.1 MB”，“102字节”等)。

例如:

{{ value|filesizeformat }}

如果值是123456789，输出将是117.7 MB。

更多信息:https://docs.djangoproject.com/en/1.10/ref/templates/builtins/#filesizeformat

我最近提出了一个避免循环的版本，使用log2来确定大小顺序，作为后缀列表的移位和索引:

from math import log2

_suffixes = ['bytes', 'KiB', 'MiB', 'GiB', 'TiB', 'PiB', 'EiB', 'ZiB', 'YiB']

def file_size(size):
    # determine binary order in steps of size 10 
    # (coerce to int, // still returns a float)
    order = int(log2(size) / 10) if size else 0
    # format file size
    # (.4g results in rounded numbers for exact matches and max 3 decimals, 
    # should never resort to exponent values)
    return '{:.4g} {}'.format(size / (1 << (order * 10)), _suffixes[order])

不过，它的可读性很可能被认为是非python化的。

如果你安装了Django，你也可以试试filesizeformat:

from django.template.defaultfilters import filesizeformat
filesizeformat(1073741824)

=>

"1.0 GB"

这个解决方案可能也会吸引你，这取决于你的思维方式:

from pathlib import Path    

def get_size(path = Path('.')):
    """ Gets file size, or total directory size """
    if path.is_file():
        size = path.stat().st_size
    elif path.is_dir():
        size = sum(file.stat().st_size for file in path.glob('*.*'))
    return size

def format_size(path, unit="MB"):
    """ Converts integers to common size units used in computing """
    bit_shift = {"B": 0,
            "kb": 7,
            "KB": 10,
            "mb": 17,
            "MB": 20,
            "gb": 27,
            "GB": 30,
            "TB": 40,}
    return "{:,.0f}".format(get_size(path) / float(1 << bit_shift[unit])) + " " + unit

# Tests and test results
>>> get_size("d:\\media\\bags of fun.avi")
'38 MB'
>>> get_size("d:\\media\\bags of fun.avi","KB")
'38,763 KB'
>>> get_size("d:\\media\\bags of fun.avi","kb")
'310,104 kb'