linecache

3 files changed, 183 insertions, 4 deletions

diff --git a/modules/language/python/exceptions.scm b/modules/language/python/exceptions.scm
index 80d1e7d..9425fea 100644
--- a/modules/language/python/exceptions.scm
+++ b/modules/language/python/exceptions.scm
@@ -14,7 +14,7 @@
 			  OverflowError RecursionError
 			  Warning DeprecationWarning BytesWarning
                           UnicodeDecodeError LookupError IndentationError
-                          KeyboardInterrupt))
+                          KeyboardInterrupt MemoryError))
 
 (define-syntax-rule (aif it p x y) (let ((it p)) (if it x y)))
 
@@ -67,6 +67,7 @@
 (define StopIteration           'StopIteration)
 (define GeneratorExit           'GeneratorExit)
 
+(define-er MemoryError          'MemoryError)
 (define-er UnicodeDecodeError   'UnicodeDecodeError)
 (define-er LookupError          'LookupError)
 (define-er IndentationError     'IndentationError)
diff --git a/modules/language/python/module/linecache.py b/modules/language/python/module/linecache.py
new file mode 100644
index 0000000..94ea0e1
--- /dev/null
+++ b/modules/language/python/module/linecache.py
@@ -0,0 +1,178 @@
+module(linecache)
+"""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"]
+
+def getline(filename, lineno, module_globals=None):
+    lines = getlines(filename, module_globals)
+    if 1 <= lineno <= len(lines):
+        return lines[lineno-1]
+    else:
+        return ''
+
+
+# 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():
+    """Clear the cache entirely."""
+
+    global cache
+    cache = {}
+
+
+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+    """Discard cache entries that are out of date.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())
+    else:
+        if 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:
+            del cache[filename]
+            continue
+        if size != stat.st_size or mtime != stat.st_mtime:
+            del cache[filename]
+
+
+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:
+            del cache[filename]
+    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:
+        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 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
diff --git a/modules/language/python/module/sys.scm b/modules/language/python/module/sys.scm
index aa4a166..d4d25b9 100644
--- a/modules/language/python/module/sys.scm
+++ b/modules/language/python/module/sys.scm
@@ -12,9 +12,9 @@
 		     stdin     stdout     stderr
 		   __stdin__ __stdout__ __stderr__
 		   exit version_info version api_version
-                   warnoptions winver _xoption
+                   warnoptions winver _xoption 
                    tarcebacklimit platform maxsize hash_info
-                   base_prefix))
+                   base_prefix path))
 
 (define-syntax stdin_
   (lambda (x)
@@ -156,7 +156,7 @@
 
 (define meta_path '())
 (define modules (@ (language python module) modules))
-(define path '())
+(define path %load-path)
 (define path_hooks '())
 (define path_importer_cache (make-hash-table))