请注意在例 8.1 “使用版本库层”中，代码可以非常容易使用svn_fs_commit_txn()提交事务。但是文件系统的API对版本库库的钩子一无所知，如果你希望你的Subversion版本库在每次提交一个事务时自动执行一些非Subversion的任务(例如，给开发者邮件组发送一个描述事务修改的邮件)，你需要使用libsvn_repos包裹的功能版本—这个功能会实际上首先运行一个如果存在的pre-commit钩子脚本，然后提交事务，最后会运行一个post-commit钩子脚本。钩子提供了一种特别的报告机制，不是真的属于核心文件系统库本身。(关于Subversion版本库钩子的更多信息，见“实现版本库钩子”一节。)
现在我们转换一下语言，例 8.2 “使用 Python 处理版本库层”使用Subversion SWIG的Python绑定实现了从版本库取得最新的版本，并且打印了取出时访问的目录。
例 8.2. 使用 Python 处理版本库层
#!/usr/bin/python """Crawl a repository, printing versioned object path names.""" import sys import os.path import svn.fs, svn.core, svn.repos def crawl_filesystem_dir(root, directory): """Recursively crawl DIRECTORY under ROOT in the filesystem, and return a list of all the paths at or below DIRECTORY.""" # Print the name of this path. print directory + "/" # Get the directory entries for DIRECTORY. entries = svn.fs.svn_fs_dir_entries(root, directory) # Loop over the entries. names = entries.keys() for name in names: # Calculate the entry's full path. full_path = directory + '/' + name # If the entry is a directory, recurse. The recursion will return # a list with the entry and all its children, which we will add to # our running list of paths. if svn.fs.svn_fs_is_dir(root, full_path): crawl_filesystem_dir(root, full_path) else: # Else it's a file, so print its path here. print full_path def crawl_youngest(repos_path): """Open the repository at REPOS_PATH, and recursively crawl its youngest revision.""" # Open the repository at REPOS_PATH, and get a reference to its # versioning filesystem. repos_obj = svn.repos.svn_repos_open(repos_path) fs_obj = svn.repos.svn_repos_fs(repos_obj) # Query the current youngest revision. youngest_rev = svn.fs.svn_fs_youngest_rev(fs_obj) # Open a root object representing the youngest (HEAD) revision. root_obj = svn.fs.svn_fs_revision_root(fs_obj, youngest_rev) # Do the recursive crawl. crawl_filesystem_dir(root_obj, "") if __name__ == "__main__": # Check for sane usage. if len(sys.argv) != 2: sys.stderr.write("Usage: %s REPOS_PATH\n" % (os.path.basename(sys.argv[0]))) sys.exit(1) # Canonicalize the repository path. repos_path = svn.core.svn_path_canonicalize(sys.argv[1]) # Do the real work. crawl_youngest(repos_path)
同样的C程序需要处理APR内存池系统，但是Python自己处理内存，Subversion的Python绑定也遵循这种习惯。在C语言中，为表示路径和条目的hash需要处理自定义的数据类型(例如APR提供的库)，但是Python有hash(叫做“dictionaries”)，并且是内置数据类型，而且还提供了一系列操作这些类型的函数，所以SWIG(通过Subversion的语言绑定层的自定义帮助)要小心的将这些自定义数据类型映射到目标语言的数据类型，这为目标语言的用户提供了一个更加直观的接口。
Subversion的Python绑定也可以用来进行工作拷贝的操作，在本章前面的小节中，我们提到过libsvn_client接口，它存在的目的就是简化编写Subversion客户端的难度，例 8.3 “一个Python状态爬虫”是一个例子，讲的是如何使用SWIG绑定创建一个扩展版本的svn status命令。
例 8.3. 一个Python状态爬虫
#!/usr/bin/env python """Crawl a working copy directory, printing status information.""" import sys import os.path import getopt import svn.core, svn.client, svn.wc def generate_status_code(status): """Translate a status value into a single-character status code, using the same logic as the Subversion command-line client.""" code_map = { svn.wc.svn_wc_status_none : ' ', svn.wc.svn_wc_status_normal : ' ', svn.wc.svn_wc_status_added : 'A', svn.wc.svn_wc_status_missing : '!', svn.wc.svn_wc_status_incomplete : '!', svn.wc.svn_wc_status_deleted : 'D', svn.wc.svn_wc_status_replaced : 'R', svn.wc.svn_wc_status_modified : 'M', svn.wc.svn_wc_status_merged : 'G', svn.wc.svn_wc_status_conflicted : 'C', svn.wc.svn_wc_status_obstructed : '~', svn.wc.svn_wc_status_ignored : 'I', svn.wc.svn_wc_status_external : 'X', svn.wc.svn_wc_status_unversioned : '?', } return code_map.get(status, '?') def do_status(wc_path, verbose): # Calculate the length of the input working copy path. wc_path_len = len(wc_path) # Build a client context baton. ctx = svn.client.svn_client_ctx_t() def _status_callback(path, status, root_path_len=wc_path_len): """A callback function for svn_client_status.""" # Print the path, minus the bit that overlaps with the root of # the status crawl text_status = generate_status_code(status.text_status) prop_status = generate_status_code(status.prop_status) print '%s%s %s' % (text_status, prop_status, path[wc_path_len + 1:]) # Do the status crawl, using _status_callback() as our callback function. svn.client.svn_client_status(wc_path, None, _status_callback, 1, verbose, 0, 0, ctx) def usage_and_exit(errorcode): """Print usage message, and exit with ERRORCODE.""" stream = errorcode and sys.stderr or sys.stdout stream.write("""Usage: %s OPTIONS WC-PATH Options: --help, -h : Show this usage message --verbose, -v : Show all statuses, even uninteresting ones """ % (os.path.basename(sys.argv[0]))) sys.exit(errorcode) if __name__ == '__main__': # Parse command-line options. try: opts, args = getopt.getopt(sys.argv[1:], "hv", ["help", "verbose"]) except getopt.GetoptError: usage_and_exit(1) verbose = 0 for opt, arg in opts: if opt in ("-h", "--help"): usage_and_exit(0) if opt in ("-v", "--verbose"): verbose = 1 if len(args) != 1: usage_and_exit(2) # Canonicalize the repository path. wc_path = svn.core.svn_path_canonicalize(args[0]) # Do the real work. try: do_status(wc_path, verbose) except svn.core.SubversionException, e: sys.stderr.write("Error (%d): %s\n" % (e[1], e[0])) sys.exit(1)