摘要：就像這樣以下將一些典型舉例說明特別說明，下面的所有操作，均是進入到如下的目錄中進行的。上面的操作發(fā)現(xiàn)這個文件在當前目錄下是不存在的，但是，用能夠返回一個絕對路徑并帶有這個不存在的文件的文件名。返回首頁上一講私有和專有

python在安裝的時候，就自帶了很多模塊，我們把這些模塊稱之為標準庫，其中，有一個是使用頻率比較高的，就是 os 。這個庫中方法和屬性眾多，有興趣的看官可以參考官方文檔：https://docs.python.org/2/library/os.html，或者在交互模式中，用dir(os)看一看。

>>> import os   #這個動作很重要，不能缺少
>>> dir(os)
["EX_CANTCREAT", "EX_CONFIG", "EX_DATAERR", "EX_IOERR", "EX_NOHOST", "EX_NOINPUT", "EX_NOPERM", "EX_NOUSER", "EX_OK", "EX_OSERR", "EX_OSFILE", "EX_PROTOCOL", "EX_SOFTWARE", "EX_TEMPFAIL", "EX_UNAVAILABLE", "EX_USAGE", "F_OK", "NGROUPS_MAX", "O_APPEND", "O_ASYNC", "O_CREAT", "O_DIRECT", "O_DIRECTORY", "O_DSYNC", "O_EXCL", "O_LARGEFILE", "O_NDELAY", "O_NOATIME", "O_NOCTTY", "O_NOFOLLOW", "O_NONBLOCK", "O_RDONLY", "O_RDWR", "O_RSYNC", "O_SYNC", "O_TRUNC", "O_WRONLY", "P_NOWAIT", "P_NOWAITO", "P_WAIT", "R_OK", "SEEK_CUR", "SEEK_END", "SEEK_SET", "TMP_MAX", "UserDict", "WCONTINUED", "WCOREDUMP", "WEXITSTATUS", "WIFCONTINUED", "WIFEXITED", "WIFSIGNALED", "WIFSTOPPED", "WNOHANG", "WSTOPSIG", "WTERMSIG", "WUNTRACED", "W_OK", "X_OK", "_Environ", "__all__", "__builtins__", "__doc__", "__file__", "__name__", "__package__", "_copy_reg", "_execvpe", "_exists", "_exit", "_get_exports_list", "_make_stat_result", "_make_statvfs_result", "_pickle_stat_result", "_pickle_statvfs_result", "_spawnvef", "abort", "access", "altsep", "chdir", "chmod", "chown", "chroot", "close", "closerange", "confstr", "confstr_names", "ctermid", "curdir", "defpath", "devnull", "dup", "dup2", "environ", "errno", "error", "execl", "execle", "execlp", "execlpe", "execv", "execve", "execvp", "execvpe", "extsep", "fchdir", "fchmod", "fchown", "fdatasync", "fdopen", "fork", "forkpty", "fpathconf", "fstat", "fstatvfs", "fsync", "ftruncate", "getcwd", "getcwdu", "getegid", "getenv", "geteuid", "getgid", "getgroups", "getloadavg", "getlogin", "getpgid", "getpgrp", "getpid", "getppid", "getresgid", "getresuid", "getsid", "getuid", "initgroups", "isatty", "kill", "killpg", "lchown", "linesep", "link", "listdir", "lseek", "lstat", "major", "makedev", "makedirs", "minor", "mkdir", "mkfifo", "mknod", "name", "nice", "open", "openpty", "pardir", "path", "pathconf", "pathconf_names", "pathsep", "pipe", "popen", "popen2", "popen3", "popen4", "putenv", "read", "readlink", "remove", "removedirs", "rename", "renames", "rmdir", "sep", "setegid", "seteuid", "setgid", "setgroups", "setpgid", "setpgrp", "setregid", "setresgid", "setresuid", "setreuid", "setsid", "setuid", "spawnl", "spawnle", "spawnlp", "spawnlpe", "spawnv", "spawnve", "spawnvp", "spawnvpe", "stat", "stat_float_times", "stat_result", "statvfs", "statvfs_result", "strerror", "symlink", "sys", "sysconf", "sysconf_names", "system", "tcgetpgrp", "tcsetpgrp", "tempnam", "times", "tmpfile", "tmpnam", "ttyname", "umask", "uname", "unlink", "unsetenv", "urandom", "utime", "wait", "wait3", "wait4", "waitpid", "walk", "write"]

在這么多的東西中，本講只關(guān)注os.path，真所謂“弱水三千，只取一瓢”，為什么這么偏愛它呢？因為它和前面已經(jīng)講過的文件操作進行配合，就能夠隨心所欲操作各個地方的文件了（關(guān)于文件，請參考：不要紅頭文件(1)、不要紅頭文件(2)）

關(guān)于os.path的屬性也不少，依然可以用dir(os.path)查看：

>>> dir(os.path)
["__all__", "__builtins__", "__doc__", "__file__", "__name__", "__package__", "_joinrealpath", "_unicode", "_varprog", "abspath", "altsep", "basename", "commonprefix", "curdir", "defpath", "devnull", "dirname", "exists", "expanduser", "expandvars", "extsep", "genericpath", "getatime", "getctime", "getmtime", "getsize", "isabs", "isdir", "isfile", "islink", "ismount", "join", "lexists", "normcase", "normpath", "os", "pardir", "pathsep", "realpath", "relpath", "samefile", "sameopenfile", "samestat", "sep", "split", "splitdrive", "splitext", "stat", "supports_unicode_filenames", "sys", "walk", "warnings"]

這么多屬性，看官可以用help()逐個查看有關(guān)信息，并了解其使用方法。下面列出常見的幾個使用方法，為看官減輕一點閱讀英文的障礙，不過，如果看官英語足夠好，請直接看原文檔。就像這樣：

>>> help(os.path.split)

split(p)
    Split a pathname.  Returns tuple "(head, tail)" where "tail" is
    everything after the final slash.  Either part may be empty.

以下將一些典型舉例說明：

特別說明，下面的所有操作，均是進入到如下的目錄中進行的。

qw@qw-Latitude-E4300:~/Documents/ITArticles/BasicPython/codes$ pwd
/home/qw/Documents/ITArticles/BasicPython/codes         #當前目錄

qw@qw-Latitude-E4300:~/Documents/ITArticles/BasicPython/codes$ python

Python 2.7.6 (default, Nov 13 2013, 19:24:16) 
[GCC 4.6.3] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> 

>>> import os.path
>>> os.path.abspath("225.py")
"/home/qw/Documents/ITArticles/BasicPython/codes/225.py"

文件 225.py 是真實存在上述路徑中的，得到了該文件的絕對路徑。但是，如果隨便提供一個不在這個目錄中的文件，又如何？

>>> os.path.isfile("225.py")
True

>>> os.path.isfile("2222.py")
False
>>> os.path.abspath("2222.py")
"/home/qw/Documents/ITArticles/BasicPython/codes/2222.py"

os.path.isfile(path)，可以判斷path中是否是文件，其實是判斷在該路徑中，是否存在那個文件，如果存在則返回True，否則False。上面的操作發(fā)現(xiàn) 2222.py 這個文件在當前目錄下是不存在的，但是，用os.path.abspaht("2222.py")能夠返回一個絕對路徑并帶有這個不存在的文件的文件名。這里不妨理解為，如果要建立這個文件，它即將被放在那個位置。

按照這樣理解，還可：

>>> os.path.abspath("/home/qw/kkkkkkkk.kk")
"/home/qw/kkkkkkkk.kk"

>>> pn = os.path.abspath("225.py")
>>> pn
"/home/qw/Documents/ITArticles/BasicPython/codes/225.py"

>>> os.path.split(pn)
("/home/qw/Documents/ITArticles/BasicPython/codes", "225.py")
>>> path, filename = os.path.split(pn)[0], os.path.split(pn)[1]
>>> path
"/home/qw/Documents/ITArticles/BasicPython/codes"
>>> filename
"225.py"

os.paht.split(),參數(shù)是目錄加文件名，就可以將路徑和文件名分開。其實，我看這個功能不是很智能，你看這樣

>>> os.path.split("/home/qw")
("/home", "qw")

>>> os.path.split("/home/qw/")
("/home/qw", "")

它就是將最后一組認為是文件名了，即最后一個/后面的就是文件名，所以第二個實驗中，文件名是空了。是不是有點傻呢？

同樣，參數(shù)中的文件或者目錄，不一定是你的電腦中真實存在的，請看：

>>> os.path.split("/foo/python/qiwsir/git.git")
("/foo/python/qiwsir", "git.git")

只要符合目錄書寫結(jié)構(gòu)，就可以分解了。

有另外兩個屬性，是os.path.split()的分別執(zhí)行，即可以分別獲得路徑和文件名，這樣讓操作更簡單了。

>>> os.path.dirname("/foo/python/qiwsir/git.git")
"/foo/python/qiwsir"
>>> os.path.basename("foo/python/qiwsir/git.git")
"git.git"

前面稍微提到了os.path.isfile()可以用來判斷一個文件是否存在，那么判斷目錄路徑是否存在，可否？可：

>>> os.path.exists("/foo/python/qiwsir")  
False
>>> os.path.exists("/home/qw/Documents")
True

判斷相關(guān)的屬性還有：

os.path.isabs(path)：判斷path是否為絕對路徑

os.paht.isdir(path)：判斷path是否為存在的目錄

將兩個或多個對象組合起來，是常見的事情，那么如何將多個路徑組合呢？如下：

>>> os.path.join("/home/python","/BasicsPython","226.md")
"/BasicsPython/226.md"

特別提醒，這個屬性的返回值中，將第一個絕對路徑忽略。

>>> os.path.join("/","/home/qw","learnpython.md")
"/home/qw/learnpython.md"

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