|
Original |
Translation |
|
91
|
Jython relies on the Java runtime so the JVM's garbage collector is used. This difference can cause some subtle porting problems if your Python code depends on the behavior of the reference counting implementation.
|
|
|
92
|
In the absence of circularities, Python programs do not need to manage memory explicitly.
|
|
|
93
|
Why doesn't Python use a more traditional garbage collection scheme? For one thing, this is not a C standard feature and hence it's not portable. (Yes, we know about the Boehm GC library. It has bits of assembler code for *most* common platforms, not for all of them, and although it is mostly transparent, it isn't completely transparent; patches are required to get Python to work with it.)
|
|
|
94
|
Traditional GC also becomes a problem when Python is embedded into other applications. While in a standalone Python it's fine to replace the standard malloc() and free() with versions provided by the GC library, an application embedding Python may want to have its *own* substitute for malloc() and free(), and may not want Python's. Right now, Python works with anything that implements malloc() and free() properly.
|
|
|
95
|
|
96
|
for file in very_long_list_of_files: f = open(file) c = f.read(1)
|
|
|
97
|
Using the current reference counting and destructor scheme, each new assignment to f closes the previous file. Using GC, this is not guaranteed. If you want to write code that will work with any Python implementation, you should explicitly close the file or use the :keyword:`with` statement; this will work regardless of GC::
|
|
|
98
|
for file in very_long_list_of_files: with open(file) as f: c = f.read(1)
|
|
|
99
|
Why isn't all memory freed when Python exits?
|
|
|
100
|
Objects referenced from the global namespaces of Python modules are not always deallocated when Python exits. This may happen if there are circular references. There are also certain bits of memory that are allocated by the C library that are impossible to free (e.g. a tool like Purify will complain about these). Python is, however, aggressive about cleaning up memory on exit and does try to destroy every single object.
|
|