如何删除 python 中的最后一行以将其保持在 10 行

Question

I have a text file that already prepends until it has 10 lines

    Line 10
    Line 9
    Line 8
    Line 7
    Line 6
    Line 5
    Line 4
    Line 3
    Line 2
    Line 1

Now if I prepend more line into this text file. It'll become 11 Line

    Line 11
    Line 10
    Line 9
    Line 8
    Line 7
    Line 6
    Line 5
    Line 4
    Line 3
    Line 2
    Line 1

And now, I want to remove the Line 1 from the file to keep it only 10 lines long. How do I do that in python?

Answer 1

Once you have read your lines, you can use slicing before writing them again with:

lines = lines[:10]  # Keep 10 first lines

Answer 2

At first I wrote the code which is Do the writing in file and then I changed it to What you've asked:

For example this is the Code that do the writing:

f = open("test.txt", "w")

lines = ["line 1 ","line 2","line 3","line 4","line 5","line 6","line 7","line 8","line 9","line 10"]
i = len(lines)-1
while( i >= 0):

    f.write(lines[i]+"\n")
    i -= 1
f.close()

output:

line 10
line 9
line 8
line 7
line 6
line 5
line 4
line 3
line 2
line 1 

Now I wanna change this to what you've asked (to delete last line):

f = open("test.txt", "w")

lines = ["line 1 ","line 2","line 3","line 4","line 5","line 6","line 7","line 8","line 9","line 10"]

#first of all you have to append new line to you list
lines.append("line 11")
lines = lines[-10:] # this is how you Select 10 last elements

i = len(lines)-1
while( i >= 0):

    f.write(lines[i]+"\n")
    i -= 1


f.close()

Output:

line 11
line 10
line 9
line 8
line 7
line 6
line 5
line 4
line 3
line 2

So as a result for selecting N last elements of list you can use this Option:

anyList = anyList[-N:]