Issue #17911: traceback module overhaul
Provide a way to seed the linecache for a PEP-302 module without actually
loading the code.
Provide a new object API for traceback, including the ability to not lookup
lines at all until the traceback is actually rendered, without any trace of the
original objects being kept alive.
diff --git a/Lib/linecache.py b/Lib/linecache.py
index 02a9eb5..33b0af7 100644
--- a/Lib/linecache.py
+++ b/Lib/linecache.py
@@ -5,6 +5,7 @@
that name.
"""
+import functools
import sys
import os
import tokenize
@@ -21,7 +22,9 @@
# The cache
-cache = {} # The cache
+# 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():
@@ -36,6 +39,9 @@
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 updatecache(filename, module_globals)
return cache[filename][2]
else:
return updatecache(filename, module_globals)
@@ -54,7 +60,11 @@
return
for filename in filenames:
- size, mtime, lines, fullname = cache[filename]
+ 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:
@@ -72,7 +82,8 @@
and return an empty list."""
if filename in cache:
- del cache[filename]
+ if len(cache[filename]) != 1:
+ del cache[filename]
if not filename or (filename.startswith('<') and filename.endswith('>')):
return []
@@ -82,27 +93,23 @@
except OSError:
basename = filename
- # Try for a __loader__, if available
- if module_globals and '__loader__' in module_globals:
- name = module_globals.get('__name__')
- loader = module_globals['__loader__']
- get_source = getattr(loader, 'get_source', None)
-
- if name and get_source:
- try:
- data = get_source(name)
- 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]
+ # 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.
@@ -132,3 +139,36 @@
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 cachable
+ 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 '__loader__' in module_globals:
+ name = module_globals.get('__name__')
+ loader = module_globals['__loader__']
+ 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