zeroinstall/support/__init__.py

   1 """
   2 Useful support routines (for internal use).
   3
   4 These functions aren't really Zero Install specific; they're things we might
   5 wish were in the standard library.
   6
   7 @since: 0.27
   8 """
   9
  10 # Copyright (C) 2009, Thomas Leonard
  11 # See the README file for details, or visit http://0install.net.
  12
  13 from zeroinstall import _
  14 import os, logging
  15
  16 def find_in_path(prog):
  17         """Search $PATH for prog.
  18         If prog is an absolute path, return it unmodified.
  19         @param prog: name of executable to find
  20         @return: the full path of prog, or None if not found
  21         @since: 0.27
  22         """
  23         if os.path.isabs(prog): return prog
  24         if os.name == "nt":
  25                 prog += '.exe'
  26         for d in os.environ.get('PATH', '/bin:/usr/bin').split(os.pathsep):
  27                 path = os.path.join(d, prog)
  28                 if os.path.isfile(path):
  29                         return path
  30         return None
  31
  32 def read_bytes(fd, nbytes, null_ok = False):
  33         """Read exactly nbytes from fd.
  34         @param fd: file descriptor to read from
  35         @param nbytes: number of bytes to read
  36         @param null_ok: if True, it's OK to receive EOF immediately (we then return None)
  37         @return: the bytes read
  38         @raise Exception: if we received less than nbytes of data
  39         """
  40         data = ''
  41         while nbytes:
  42                 got = os.read(fd, nbytes)
  43                 if not got:
  44                         if null_ok and not data:
  45                                 return None
  46                         raise Exception(_("Unexpected end-of-stream. Data so far %(data)s; expecting %(bytes)d bytes more.")
  47                                         % {'data': repr(data), 'bytes': nbytes})
  48                 data += got
  49                 nbytes -= len(got)
  50         logging.debug(_("Message received: %r"), data)
  51         return data
  52
  53 def pretty_size(size):
  54         """Format a size for printing.
  55         @param size: the size in bytes
  56         @type size: int (or None)
  57         @return: the formatted size
  58         @rtype: str
  59         @since: 0.27"""
  60         if size is None:
  61                 return '?'
  62         if size < 2048:
  63                 return _('%d bytes') % size
  64         size = float(size)
  65         for unit in (_('KB'), _('MB'), _('GB'), _('TB')):
  66                 size /= 1024
  67                 if size < 2048:
  68                         break
  69         return _('%(size).1f %(unit)s') % {'size': size, 'unit': unit}
  70
  71 def ro_rmtree(root):
  72         """Like shutil.rmtree, except that we also delete read-only items.
  73         @param root: the root of the subtree to remove
  74         @type root: str
  75         @since: 0.28"""
  76         import shutil
  77         import platform
  78         if platform.system() == 'Windows':
  79                 for main, dirs, files in os.walk(root):
  80                         for i in files + dirs:
  81                                 os.chmod(os.path.join(main, i), 0o700)
  82                 os.chmod(root, 0o700)
  83         else:
  84                 for main, dirs, files in os.walk(root):
  85                         os.chmod(main, 0o700)
  86         shutil.rmtree(root)
  87
  88 def raise_with_traceback(ex, tb):
  89         """Raise an exception in a way that works on Python 2 and Python 3"""
  90         if hasattr(ex, 'with_traceback'):
  91                 raise ex.with_traceback(tb)                     # Python 3
  92         exec("raise ex, None, tb", {'ex': ex, 'tb': tb})        # Python 2
  93         assert 0
  94
  95 def portable_rename(src, dst):
  96         """Rename 'src' to 'dst', which must be on the same filesystem.
  97         On POSIX systems, this operation is atomic.
  98         On Windows, do the best we can by deleting dst and then renaming.
  99         @since: 1.9"""
 100         if os.name == "nt" and os.path.exists(dst):
 101                 os.unlink(dst)
 102         os.rename(src, dst)