Lib/linecache.py

   1 """Cache lines from files.
   2
   3 This is intended to read lines from modules imported -- hence if a filename
   4 is not found, it will look down the module search path for a file by
   5 that name.
   6 """
   7
   8 import sys
   9 import os
  10 import tokenize
  11
  12 __all__ = ["getline", "clearcache", "checkcache"]
  13
  14 def getline(filename, lineno, module_globals=None):
  15     lines = getlines(filename, module_globals)
  16     if 1 <= lineno <= len(lines):
  17         return lines[lineno-1]
  18     else:
  19         return ''
  20
  21
  22 # The cache
  23
  24 cache = {} # The cache
  25
  26
  27 def clearcache():
  28     """Clear the cache entirely."""
  29
  30     global cache
  31     cache = {}
  32
  33
  34 def getlines(filename, module_globals=None):
  35     """Get the lines for a file from the cache.
  36     Update the cache if it doesn't contain an entry for this file already."""
  37
  38     if filename in cache:
  39         return cache[filename][2]
  40     else:
  41         return updatecache(filename, module_globals)
  42
  43
  44 def checkcache(filename=None):
  45     """Discard cache entries that are out of date.
  46     (This is not checked upon each call!)"""
  47
  48     if filename is None:
  49         filenames = list(cache.keys())
  50     else:
  51         if filename in cache:
  52             filenames = [filename]
  53         else:
  54             return
  55
  56     for filename in filenames:
  57         size, mtime, lines, fullname = cache[filename]
  58         if mtime is None:
  59             continue   # no-op for files loaded via a __loader__
  60         try:
  61             stat = os.stat(fullname)
  62         except os.error:
  63             del cache[filename]
  64             continue
  65         if size != stat.st_size or mtime != stat.st_mtime:
  66             del cache[filename]
  67
  68
  69 def updatecache(filename, module_globals=None):
  70     """Update a cache entry and return its list of lines.
  71     If something's wrong, print a message, discard the cache entry,
  72     and return an empty list."""
  73
  74     if filename in cache:
  75         del cache[filename]
  76     if not filename or (filename.startswith('<') and filename.endswith('>')):
  77         return []
  78
  79     fullname = filename
  80     try:
  81         stat = os.stat(fullname)
  82     except OSError:
  83         basename = filename
  84
  85         # Try for a __loader__, if available
  86         if module_globals and '__loader__' in module_globals:
  87             name = module_globals.get('__name__')
  88             loader = module_globals['__loader__']
  89             get_source = getattr(loader, 'get_source', None)
  90
  91             if name and get_source:
  92                 try:
  93                     data = get_source(name)
  94                 except (ImportError, IOError):
  95                     pass
  96                 else:
  97                     if data is None:
  98                         # No luck, the PEP302 loader cannot find the source
  99                         # for this module.
 100                         return []
 101                     cache[filename] = (
 102                         len(data), None,
 103                         [line+'\n' for line in data.splitlines()], fullname
 104                     )
 105                     return cache[filename][2]
 106
 107         # Try looking through the module search path, which is only useful
 108         # when handling a relative filename.
 109         if os.path.isabs(filename):
 110             return []
 111
 112         for dirname in sys.path:
 113             try:
 114                 fullname = os.path.join(dirname, basename)
 115             except (TypeError, AttributeError):
 116                 # Not sufficiently string-like to do anything useful with.
 117                 continue
 118             try:
 119                 stat = os.stat(fullname)
 120                 break
 121             except os.error:
 122                 pass
 123         else:
 124             return []
 125     try:
 126         with open(fullname, 'rb') as fp:
 127             coding, line = tokenize.detect_encoding(fp.readline)
 128         with open(fullname, 'r', encoding=coding) as fp:
 129             lines = fp.readlines()
 130     except IOError:
 131         pass
 132     if lines and not lines[-1].endswith('\n'):
 133         lines[-1] += '\n'
 134     size, mtime = stat.st_size, stat.st_mtime
 135     cache[filename] = size, mtime, lines, fullname
 136     return lines