time.time（）和file.getmtime（）之間的關係？

Question

我從dkfileutils寫Path.touch測試：

class Path(str): 
    def touch(self, mode=0o666, exist_ok=True): 
     """Create this file with the given access mode, if it doesn't exist. 
      (based on https://github.com/python/cpython/blob/master/Lib/pathlib.py) 
     """ 
     if exist_ok: 
      # First try to bump modification time 
      # Implementation note: GNU touch uses the UTIME_NOW option of 
      # the utimensat()/futimens() functions. 
      try: 
       os.utime(self, None) 
      except OSError: 
       # Avoid exception chaining 
       pass 
      else: 
       return 
     flags = os.O_CREAT | os.O_WRONLY 
     if not exist_ok: 
      flags |= os.O_EXCL 
     fd = os.open(self, flags, mode) 
     os.close(fd) 

我曾嘗試以下的變化..

def test_touch(): 
    before = time.time() 
    with open('a', 'w') as fp: 
     fp.write('a') 
    after = time.time() 

    assert before <= after 

    a = Path('a') 
    a_before_touch = a.getmtime() 
    assert before <= a_before_touch <= after 

    a.touch() 
    after_touch = time.time() 
    a_after_touch = a.getmtime() 

    assert a_before_touch <= a_after_touch 
    assert a_after_touch >= after 
    assert a_after_touch <= after_touch 

但它不停地進行故障（https://travis-ci.org/datakortet/dkfileutils/builds），運行68：

>   assert before <= a_before_touch <= after 
E   assert 1489532961.064958 <= 1489532961.064464 

運行67

>   assert a_after_touch > after 
E   assert 1489532462.412086 > 1489532462.412933 

運行66

>   assert a_after_touch > after 
E   assert 1489532286.6042855 > 1489532286.606766 

我只是在假設了time.time（）和file.getmtime傻（）有關係嗎？

Answer 1

所有文件系統只分配有限數量的位來存儲文件時間戳;在一些較舊的文件系統中，分辨率是一秒或更差。一般來說，它不會像直接讀取時鐘一樣提供相同的分辨率。