Python基础知识 - 为什么不是我的文件打印的内容？

Question

I'm running this from eclipse, the file name I'm working with is ex16_text.txt (yes I type it in correctly. It writes to the file correctly (the input appears), but the "print txt.read()" doesn't seem to do anything (prints a blank line), see the output after the code:

filename = raw_input("What's the file name we'll be working with?")

print "we're going to erase %s" % filename

print "opening the file"
target = open(filename, 'w')

print "erasing the file"
target.truncate()

print "give me 3 lines to replace file contents:"

line1 = raw_input("line 1: ")
line2 = raw_input("line 2: ")
line3 = raw_input("line 3: ")

print "writing lines to file"

target.write(line1+"\n")
target.write(line2+"\n")
target.write(line3)

#file read
txt = open(filename)

print "here are the contents of the %s file:" % filename
print txt.read()

target.close()

Output:

What's the file name we'll be working with?ex16_text.txt we're going to erase ex16_text.txt opening the file erasing the file give me 3 lines to replace file contents: line 1: three line 2: two line 3: one writing lines to file here are the contents of the ex16_text.txt file:

Answer 1

You should flush the file after you have written to it to ensure that the bytes have been written. Also read the warning:

Note: flush() does not necessarily write the file's data to disk. Use flush() followed by os.fsync() to ensure this behavior.

You should also close the file if you have finished writing to it and want to open it again with read only access. Note that closing the file also flushes - if you close it then you don't need to flush first.

In Python 2.6 or newer you can use the with statement to automatically close the file:

with open(filename, 'w') as target:
    target.write('foo')
    # etc...

# The file is closed when the control flow leaves the "with" block

with open(filename, 'r') as txt:
    print txt.read()

Answer 2

target.write(line2+"\n")
target.write(line3)
target.close() #<------- You need to close the file when you're done writing.
#file read
txt = open(filename)