Readline feature in Directory Lister class

问题

The below class is a dynamic attribute generating directory walker by Anurag.

import os

class DirLister(object):
    def __init__(self, root):
        self.root = root
        self._list = None

    def __getattr__(self, name):
        try:
            var = super(DirLister).__getattr__(self, name)
            return var
        except AttributeError:
            return DirLister(os.path.join(self.root, name))

    def __str__(self):
        self._load()
        return str(self._list)

    def _load(self):
        """
        load once when needed
        """
        if self._list is not None:
            return
        self._list = os.listdir(self.root) # list root someway

root = DirLister("/")
print root.etc.apache

Is there a way to add other complex functions to the DirLister by Anurag above? So when it gets to a file say testdir/j/p, it prints out the first line of file p.

[IN] print testdir.j.p
[OUT] First Line of p

I have made a class for printing out the first line of the file:

class File:
    def __init__(self, path):
        """Read the first line in desired path"""
        self.path = path
        f = open(path, 'r')
        self.first_line = f.readline()
        f.close()

    def __repr__(self):
        """Display the first line"""
        return self.first_line

Just need to know how to incorporate it in the class below. Thank you.

回答1:

You should be able to accomplish this by checking to see if self.root is a file or a directory in _load(). Read the first line if it is a file and do os.listdir() if it is a directory. Try the following:

import os

class DirLister(object):
    def __init__(self, root):
        self.root = root
        self._data = None

    def __getattr__(self, name):
        try:
            var = super(DirLister).__getattr__(self, name)
            return var
        except AttributeError:
            return DirLister(os.path.join(self.root, name))

    def __str__(self):
        self._load()
        return str(self._data)

    def _load(self):
        """
        load once when needed
        """
        if self._data is not None:
            return
        if os.path.isfile(self.root):
            f = File(self.data)
            self._data = f.first_line
        else:
            self._data = os.listdir(self.root) # list root someway

I used your File class, but you could also just put the code for getting the first line in _load() instead of having a separate class to do it. Note that I also renamed _list to _data, since it will not always represent a list of files anymore.

来源：https://stackoverflow.com/questions/8524311/readline-feature-in-directory-lister-class