to read line from file without getting “\n” appended at the end [duplicate]

问题

My file is "xml.txt" with following contents:

books.xml 
news.xml
mix.xml

if I use readline() function it appends "\n" at the name of all the files which is an error because I want to open the files contained within the xml.txt. I wrote this:

fo = open("xml.tx","r")
for i in range(count.__len__()): #here count is one of may arrays that i'm using
    file = fo.readline()
    find_root(file) # here find_root is my own created function not displayed here

error encountered on running this code:

IOError: [Errno 2] No such file or directory: 'books.xml\n'

回答1:

To remove just the newline at the end:

line = line.rstrip('\n')

The reason readline keeps the newline character is so you can distinguish between an empty line (has the newline) and the end of the file (empty string).

回答2:

From Best method for reading newline delimited files in Python and discarding the newlines?

lines = open(filename).read().splitlines()

回答3:

You could use the .rstrip() method of string objects to get a version with trailing whitespace (including newlines) removed.

E.g.:

find_root(file.rstrip())

回答4:

I timed it just for curiosity. Below are the results for a vary large file.

tldr; File read then split seems to be the fastest approach on a large file.

with open(FILENAME, "r") as file:
    lines = file.read().split("\n")

However, if you need to loop through the lines anyway then you probably want:

with open(FILENAME, "r") as file:
    for line in file:
        line = line.rstrip("\n")

Python 3.4.2

import timeit


FILENAME = "mylargefile.csv"
DELIMITER = "\n"


def splitlines_read():
    """Read the file then split the lines from the splitlines builtin method.

    Returns:
        lines (list): List of file lines.
    """
    with open(FILENAME, "r") as file:
        lines = file.read().splitlines()
    return lines
# end splitlines_read

def split_read():
    """Read the file then split the lines.

    This method will return empty strings for blank lines (Same as the other methods).
    This method may also have an extra additional element as an empty string (compared to
    splitlines_read).

    Returns:
        lines (list): List of file lines.
    """
    with open(FILENAME, "r") as file:
        lines = file.read().split(DELIMITER)
    return lines
# end split_read

def strip_read():
    """Loop through the file and create a new list of lines and removes any "\n" by rstrip

    Returns:
        lines (list): List of file lines.
    """
    with open(FILENAME, "r") as file:
        lines = [line.rstrip(DELIMITER) for line in file]
    return lines
# end strip_readline

def strip_readlines():
    """Loop through the file's read lines and create a new list of lines and removes any "\n" by
    rstrip. ... will probably be slower than the strip_read, but might as well test everything.

    Returns:
        lines (list): List of file lines.
    """
    with open(FILENAME, "r") as file:
        lines = [line.rstrip(DELIMITER) for line in file.readlines()]
    return lines
# end strip_readline

def compare_times():
    run = 100
    splitlines_t = timeit.timeit(splitlines_read, number=run)
    print("Splitlines Read:", splitlines_t)

    split_t = timeit.timeit(split_read, number=run)
    print("Split Read:", split_t)

    strip_t = timeit.timeit(strip_read, number=run)
    print("Strip Read:", strip_t)

    striplines_t = timeit.timeit(strip_readlines, number=run)
    print("Strip Readlines:", striplines_t)
# end compare_times

def compare_values():
    """Compare the values of the file.

    Note: split_read fails, because has an extra empty string in the list of lines. That's the only
    reason why it fails.
    """
    splr = splitlines_read()
    sprl = split_read()
    strr = strip_read()
    strl = strip_readlines()

    print("splitlines_read")
    print(repr(splr[:10]))

    print("split_read", splr == sprl)
    print(repr(sprl[:10]))

    print("strip_read", splr == strr)
    print(repr(strr[:10]))

    print("strip_readline", splr == strl)
    print(repr(strl[:10]))
# end compare_values

if __name__ == "__main__":
    compare_values()
    compare_times()

Results:

run = 1000
Splitlines Read: 201.02846901328783
Split Read: 137.51448011841822
Strip Read: 156.18040391519133
Strip Readline: 172.12281272950372

run = 100
Splitlines Read: 19.956802833188124
Split Read: 13.657361738959867
Strip Read: 15.731161020969516
Strip Readlines: 17.434831199281092

run = 100
Splitlines Read: 20.01516321280158
Split Read: 13.786344555543899
Strip Read: 16.02410587620824
Strip Readlines: 17.09326775703279

File read then split seems to be the fastest approach on a large file.

Note: read then split("\n") will have an extra empty string at the end of the list.

Note: read then splitlines() checks for more then just "\n" possibly "\r\n".

回答5:

It's better style to use a context manager for the file, and len() instead of calling .__len__()

with open("xml.tx","r") as fo:
    for i in range(len(count)): #here count is one of may arrays that i'm using
        file = next(fo).rstrip("\n")
        find_root(file) # here find_root is my own created function not displayed here

回答6:

To remove the newline character fro the end you could also use something like this:

for line in file:
   print line[:-1]

回答7:

A use case with @Lars Wirzenius's answer:

with open("list.txt", "r") as myfile:
    for lines in myfile:
        lines = lines.rstrip('\n')    # the trick
        try:
            with open(lines) as myFile:
                print "ok"
        except IOError as e:
            print "files does not exist"

回答8:

# mode : 'r', 'w', 'a'
f = open("ur_filename", "mode")
for t in f:
    if(t):
        fn.write(t.rstrip("\n"))

"If" condition will check whether the line has string or not, if yes next line will strip the "\n" at the end and write to a file. Code Tested. ;)

来源：https://stackoverflow.com/questions/11280282/to-read-line-from-file-without-getting-n-appended-at-the-end

标签

python

Linux

file-io

ubuntu-10.04