Python handling newline and tab characters when writing to file

问题

I am writing some text (which includes \n and \t characters) taken from one source file onto a (text) file ; for example:

source file (test.cpp):

/*
 * test.cpp
 *
 *    2013.02.30
 *
 */

is taken from the source file and stored in a string variable like so

test_str = "/*\n test.cpp\n *\n *\n *\n\t2013.02.30\n *\n */\n"

which when I write onto a file using

    with open(test.cpp, 'a') as out:
        print(test_str, file=out)

is being written with the newline and tab characters converted to new lines and tab spaces (exactly like test.cpp had them) whereas I want them to remain \n and \t exactly like the test_str variable holds them in the first place.

Is there a way to achieve that in Python when writing to a file these 'special characters' without them being translated?

回答1:

You can use str.encode:

with open('test.cpp', 'a') as out:
    print(test_str.encode('unicode_escape').decode('utf-8'), file=out)

This'll escape all the Python recognised special escape characters.

Given your example:

>>> test_str = "/*\n test.cpp\n *\n *\n *\n\t2013.02.30\n *\n */\n"
>>> test_str.encode('unicode_escape')
b'/*\\n test.cpp\\n *\\n *\\n *\\n\\t2013.02.30\\n *\\n */\\n'

回答2:

Use replace(). And since you need to use it multiple times, you might want to look at this.

test_str = "/*\n test.cpp\n *\n *\n *\n\t2013.02.30\n *\n */\n"
with open("somefile", "w") as f:
    test_str = test_str.replace('\n','\\n')
    test_str = test_str.replace('\t','\\t')
    f.write(test_str)

回答3:

I want them to remain \n and \t exactly like the test_str variable holds them in the first place.

test_str does NOT contain the backslash \ + t (two characters). It contains a single character ord('\t') == 9 (the same character as in the test.cpp). Backslash is special in Python string literals e.g., u'\U0001f600' is NOT ten characters—it is a single character 😀 Don't confuse a string object in memory during runtime and its text representation as a string literal in Python source code.

JSON could be a better alternative than unicode-escape encoding to store text (more portable) i.e., use:

import json

with open('test.json', 'w') as file:
    json.dump({'test.cpp': test_str}, file)

instead of test_str.encode('unicode_escape').decode('ascii').

To read json back:

with open('test.json') as file:
    test_str = json.load(file)['test.cpp']

来源：https://stackoverflow.com/questions/36971758/python-handling-newline-and-tab-characters-when-writing-to-file

标签

python

python-3.x

newline