多行字符串连接并写入文本文件

Question

I am using the os library of python to help me do the following:

1. Ask the user for a path.
2. Print all the directories and files included in it.
3. Save the information in a text file.

this is my code:

import os
text = 'List:'
def print_tree(dir_path,text1):
    for name in os.listdir(dir_path):
        full_path = os.path.join(dir_path, name)        

        x = name.find('.')
        if x!= -1:
            print name #replace with full path if needed
            text1 = text1 + name
        else:
            print '------------------------------------'
            text1 = text1 + '------------------------------------' 
            print name
            text1 = text1 + name 

        if os.path.isdir(full_path):
            os.path.split(name)
            print '------------------------------------'
            text1 = text1 + '------------------------------------'
            print_tree(full_path,text1)

path = raw_input('give me a dir path')
print_tree(path,text)
myfile = open('text.txt','w')
myfile.write(text)

I have two problems. First, although there's no error whatsoever, the only thing that actually exists in the text file after running this is 'List:'. Also i don't know how to use string concatenation in order to put each file name on a different line. What am i missing? How can i accomplish this?

Answer 1

Strings are immutable in Python, and the += operator on them is just an illusion. You can concatenate a string all you want in the function, but unless you return it, the string outside the function will not change: text1 = text1 + 'blah' creates a new string, and assigns its reference to text1 . The string outside the function has not changed. The solution is to build up a string and then return it:

import os
text = 'List:' + os.linesep
def print_tree(dir_path,text1):
    for name in os.listdir(dir_path):
        full_path = os.path.join(dir_path, name)        

        x = name.find('.')
        if x!= -1:
            print name #replace with full path if needed
            text1 = text1 + name + os.linesep
        else:
            print '------------------------------------'
            text1 = text1 + '------------------------------------' + os.linesep
            print name
            text1 = text1 + name + os.linesep

        if os.path.isdir(full_path):
            os.path.split(name)
            print '------------------------------------'
            text1 = text1 + '------------------------------------' + os.linesep
            text1 = print_tree(full_path,text1)
    return text1

path = raw_input('give me a dir path')
text = print_tree(path,text)
myfile = open('text.txt','w')
myfile.write(text)

I have also take the liberty of appending os.linesep to your concatenated strings. This is done by default by print , so if you want things to look the same, it is a good idea.