Writing to a file which is open in read and write mode altering the structure

问题

I have a text file, which has the following, contents:

joe satriani is god 
steve vai is god
steve morse is god
steve lukather is god

I wanted to write a code in python, which will change the file lines like:

joe satriani is god ,absolutely man ..
steve vai is god,absolutely man ..
steve morse is god,absolutely man ..
steve lukather is god,absolutely man ..

I had tried doing such earlier once and I had not gotten the desired outcome. So, first I tried writing a code, which would just append "absolutely man" at the end of only the first line.

So, the following is my code:

jj = open('readwrite.txt', 'r+')

jj.seek(1)
n = jj.read()
print(" yiuiuiuoioio \n") #just for debugging
print(n)

f = n.split("\n" , n.count("\n")) #to see what I am getting
print(f)   #As it turns out read returns the whole content as a string
print(len(f[0])) # just for debugging
jj.seek(len(f[0])) #take it to the end of first line
posy = jj.tell() # to see if it actually takes it 
print(posy)
jj.write(" Absolutely ..man ")

But on executing the code, my file changes to the following:

joe satriani is god Absolutely ..man d
steve morse is god
steve lukather is god

The second line is being overwritten. How to append to one string at the end of one line?

I thought of opening the file in read and append mode but it would overwrite the existing file. I do not want to read strings from this file and write the into another file by appending. How to append or alter the lines of a file?

Is there any way to do it without any packages?

回答1:

this is the solution if you want to write to the same file

  file_lines = []
    with open('test.txt', 'r') as file:
        for line in file.read().split('\n'):
            file_lines.append(line+ ", absolutely man ..")
    with open('test.txt', 'w') as file:
        for i in file_lines:
            file.write(i+'\n')

this is the solution if you want to write into a different file

with open('test.txt', 'r') as file:
    for line in file.read().split('\n'):
        with open('test2.txt', 'a') as second_file:
            second_file.write(line+ ", absolutely man ..\n")

回答2:

given_str = 'absolutely man ..'
text = ''.join([x[:-1]+given_str+x[-1] for x in open('file.txt')])
with open('file.txt', 'w') as file:
    file.write(text)

回答3:

tried to write something with seek. you were just rewriting instead of inserting, so you'll have to copy the end of the file after writing your text

jj = open('readwrite.txt', 'r+')
data = jj.read()

r_ptr = 0
w_ptr = 0
append_text = " Absolutely ..man \n"
len_append = len(append_text)
for line in data.split("\n"): #to see what I am getting
    r_ptr += len(line)+1
    w_ptr += len(line)
    jj.seek(w_ptr)
    jj.write(append_text+data[r_ptr:])
    w_ptr += len_append

来源：https://stackoverflow.com/questions/51009492/writing-to-a-file-which-is-open-in-read-and-write-mode-altering-the-structure

标签

python

file