"""Cache lines from Python source files.
This is intended to read lines from modules imported -- hence if a filename
is not found, it will look down the module search path for a file by
that name.
"""
import functools
import sys
import os
import tokenize
__all__ = ["getline", "clearcache", "checkcache", "lazycache"]
# The cache. Maps filenames to either a thunk which will provide source code,
# or a tuple (size, mtime, lines, fullname) once loaded.
cache = {}
def clearcache():
"""Clear the cache entirely."""
cache.clear()
def getline(filename, lineno, module_globals=None):
"""Get a line for a Python source file from the cache.
Update the cache if it doesn't contain an entry for this file already."""
lines = getlines(filename, module_globals)
if 1 <= lineno <= len(lines):
return lines[lineno - 1]
return ''
def getlines(filename, module_globals=None):
"""Get the lines for a Python source file from the cache.
Update the cache if it doesn't contain an entry for this file already."""
if filename in cache:
entry = cache[filename]
if len(entry) != 1:
return cache[filename][2]
try:
return updatecache(filename, module_globals)
except MemoryError:
clearcache()
return []
def checkcache(filename=None):
"""Discard cache entries that are out of date.
(This is not checked upon each call!)"""
if filename is None:
filenames = list(cache.keys())
elif filename in cache:
filenames = [filename]
else:
return
for filename in filenames:
entry = cache[filename]
if len(entry) == 1:
# lazy cache entry, leave it lazy.
continue
size, mtime, lines, fullname = entry
if mtime is None:
continue # no-op for files loaded via a __loader__
try:
stat = os.stat(fullname)
except OSError:
cache.pop(filename, None)
continue
if size != stat.st_size or mtime != stat.st_mtime:
cache.pop(filename, None)
def updatecache(filename, module_globals=None):
"""Update a cache entry and return its list of lines.
If something's wrong, print a message, discard the cache entry,
and return an empty list."""
if filename in cache:
if len(cache[filename]) != 1:
cache.pop(filename, None)
if not filename or (filename.startswith('<') and filename.endswith('>')):
return []
fullname = filename
try:
stat = os.stat(fullname)
except OSError:
basename = filename
# Realise a lazy loader based lookup if there is one
# otherwise try to lookup right now.
if lazycache(filename, module_globals):
try:
data = cache[filename][0]()
except (ImportError, OSError):
pass
else:
if data is None:
# No luck, the PEP302 loader cannot find the source
# for this module.
return []
cache[filename] = (
len(data),
None,
[line + '\n' for line in data.splitlines()],
fullname
)
return cache[filename][2]
# Try looking through the module search path, which is only useful
# when handling a relative filename.
if os.path.isabs(filename):
return []
for dirname in sys.path:
try:
fullname = os.path.join(dirname, basename)
except (TypeError, AttributeError):
# Not sufficiently string-like to do anything useful with.
continue
try:
stat = os.stat(fullname)
break
except OSError:
pass
else:
return []
try:
with tokenize.open(fullname) as fp:
lines = fp.readlines()
except (OSError, UnicodeDecodeError, SyntaxError):
return []
if lines and not lines[-1].endswith('\n'):
lines[-1] += '\n'
size, mtime = stat.st_size, stat.st_mtime
cache[filename] = size, mtime, lines, fullname
return lines
def lazycache(filename, module_globals):
"""Seed the cache for filename with module_globals.
The module loader will be asked for the source only when getlines is
called, not immediately.
If there is an entry in the cache already, it is not altered.
:return: True if a lazy load is registered in the cache,
otherwise False. To register such a load a module loader with a
get_source method must be found, the filename must be a cacheable
filename, and the filename must not be already cached.
"""
if filename in cache:
if len(cache[filename]) == 1:
return True
else:
return False
if not filename or (filename.startswith('<') and filename.endswith('>')):
return False
# Try for a __loader__, if available
if module_globals and '__name__' in module_globals:
name = module_globals['__name__']
if (loader := module_globals.get('__loader__')) is None:
if spec := module_globals.get('__spec__'):
try:
loader = spec.loader
except AttributeError:
pass
get_source = getattr(loader, 'get_source', None)
if name and get_source:
get_lines = functools.partial(get_source, name)
cache[filename] = (get_lines,)
return True
return False
