"""Cache lines from files.

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This is intended to read lines from modules imported -- hence if a filename

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is not found, it will look down the module search path for a file by

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that name.

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"""

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import sys

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import os

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__all__ = ["getline", "clearcache", "checkcache"]

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def getline(filename, lineno, module_globals=None):

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lines = getlines(filename, module_globals)

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if 1 <= lineno <= len(lines):

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return lines[lineno-1]

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else:

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return ''

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# The cache

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cache = {} # The cache

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def clearcache():

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"""Clear the cache entirely."""

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global cache

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cache = {}

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def getlines(filename, module_globals=None):

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"""Get the lines for a file from the cache.

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Update the cache if it doesn't contain an entry for this file already."""

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if filename in cache:

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return cache[filename][2]

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try:

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return updatecache(filename, module_globals)

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except MemoryError:

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clearcache()

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return []

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def checkcache(filename=None):

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"""Discard cache entries that are out of date.

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(This is not checked upon each call!)"""

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if filename is None:

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filenames = cache.keys()

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else:

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if filename in cache:

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filenames = [filename]

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else:

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return

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for filename in filenames:

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size, mtime, lines, fullname = cache[filename]

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if mtime is None:

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continue # no-op for files loaded via a __loader__

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try:

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stat = os.stat(fullname)

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except os.error:

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del cache[filename]

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continue

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if size != stat.st_size or mtime != stat.st_mtime:

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del cache[filename]

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def updatecache(filename, module_globals=None):

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"""Update a cache entry and return its list of lines.

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If something's wrong, print a message, discard the cache entry,

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and return an empty list."""

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if filename in cache:

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del cache[filename]

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if not filename or (filename.startswith('<') and filename.endswith('>')):

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return []

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fullname = filename

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try:

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stat = os.stat(fullname)

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except OSError:

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basename = filename

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# Try for a __loader__, if available

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if module_globals and '__loader__' in module_globals:

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name = module_globals.get('__name__')

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loader = module_globals['__loader__']

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get_source = getattr(loader, 'get_source', None)

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if name and get_source:

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try:

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data = get_source(name)

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except (ImportError, IOError):

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pass

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else:

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if data is None:

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# No luck, the PEP302 loader cannot find the source

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# for this module.

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return []

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cache[filename] = (

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len(data), None,

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[line+'\n' for line in data.splitlines()], fullname

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)

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return cache[filename][2]

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# Try looking through the module search path, which is only useful

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# when handling a relative filename.

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if os.path.isabs(filename):

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return []

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for dirname in sys.path:

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# When using imputil, sys.path may contain things other than

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# strings; ignore them when it happens.

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try:

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fullname = os.path.join(dirname, basename)

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except (TypeError, AttributeError):

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# Not sufficiently string-like to do anything useful with.

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continue

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try:

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stat = os.stat(fullname)

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break

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except os.error:

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pass

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else:

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return []

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try:

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with open(fullname, 'rU') as fp:

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lines = fp.readlines()

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except IOError:

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return []

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if lines and not lines[-1].endswith('\n'):

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lines[-1] += '\n'

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size, mtime = stat.st_size, stat.st_mtime

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cache[filename] = size, mtime, lines, fullname

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return lines

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