Programming-Python

本文作为 programming python(4th edition) 的读书笔记。

system programming:#

here is the nav of the following 5 chapters:

  • In this chapter, I’ll introduce the main system-related modules in overview fashion. We’ll meet some of the most commonly used system tools here for the first time.
  • In Chapter 3, we continue exploring the basic system interfaces by studying their role in core system programming concepts: streams, command-line arguments, environment variables, and so on.
  • Chapter 4 focuses on the tools Python provides for processing files, directories, and directory trees.
  • In Chapter 5, we’ll move on to cover Python’s standard tools for parallel processing—processes, threads, queues, pipes, signals, and more.
  • Chapter 6 wraps up by presenting a collection of complete system-oriented programs. The examples here are larger and more realistic, and they use the tools introduced in the prior four chapters to perform real, pratical tasks. This collection includes both general system scripts, as well as scripts for processing directories of files.

system scripting overview:#

Most system-level interfaces in python are shipped in two modules: sys and os. There are also some other modules belonging to this domain too. Such as glob(for filename expansion),socket(for network connections and Inter-Process Communication),threading+_thread+queue(for running and synchronizing concurrent threads),time+timeit(for accessing system time details),subprocess+multiprocessing(for lauching and controlling parallel processes)…

Some built-in functions, such as the open function, serve as interfaces to the underlying system (e.g., the file system). When we want to learn about these functions or modules, Python provides tools to interactively fetch their attributes and documentation strings. Here is a clarification:

1
2
3
>>> import sys
>>> dir(sys)
['__breakpointhook__', '__displayhook__', '__doc__', '__excepthook__', '__interactivehook__', '__loader__', '__name__', '__package__', '__spec__', '__stderr__', '__stdin__', '__stdout__', '__unraisablehook__', '_base_executable', '_clear_type_cache', '_current_frames', '_debugmallocstats', '_enablelegacywindowsfsencoding', '_framework', '_getframe', '_git', '_home', '_xoptions', 'addaudithook', 'api_version', 'argv', 'audit', 'base_exec_prefix', 'base_prefix', 'breakpointhook', 'builtin_module_names', 'byteorder', 'call_tracing', 'copyright', 'displayhook', 'dllhandle', 'dont_write_bytecode', 'exc_info', 'excepthook', 'exec_prefix', 'executable', 'exit', 'flags', 'float_info', 'float_repr_style', 'get_asyncgen_hooks', 'get_coroutine_origin_tracking_depth', 'getallocatedblocks', 'getdefaultencoding', 'getfilesystemencodeerrors', 'getfilesystemencoding', 'getprofile', 'getrecursionlimit', 'getrefcount', 'getsizeof', 'getswitchinterval', 'gettrace', 'getwindowsversion', 'hash_info', 'hexversion', 'implementation', 'int_info', 'intern', 'is_finalizing', 'maxsize', 'maxunicode', 'meta_path', 'modules', 'path', 'path_hooks', 'path_importer_cache', 'platform', 'platlibdir', 'prefix', 'ps1', 'ps2', 'pycache_prefix', 'set_asyncgen_hooks', 'set_coroutine_origin_tracking_depth', 'setprofile', 'setrecursionlimit', 'setswitchinterval', 'settrace', 'stderr', 'stdin', 'stdout', 'thread_info', 'unraisablehook', 'version', 'version_info', 'warnoptions', 'winver']

The __doc__ built-in attribute contains the documentation of a modules. And help() function is also useful to learn new modules.

In system programming, string methods are widely used. For example,

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
"""
split and interactively page a string or file of text
"""

def more(text,numlines=15):
    lines=text.splitlines()
    while(lines):
        chunk=lines[:numlines]
        lines=lines[numslines:]
        for line in chunk: print(line)
        if line and input('More?') not in ['y','Y']:break

if __name__ == '__main__':
    import sys
    more(open(sys.argv[1]).read(),10)

We use splitlines() to split text by line. It is very similar when compared with split('\n').