How to delete specific lines from a text file in python

Question

This is the text written in a text file. I want to delete specific lines for example from line no. 2 to 4 and write the rest as it is on the txt file.

Q.A ladder placed against a wall such that it reaches the top of the wall of height 6 m and the ladder is inclined at an angle of 60 degree. Find how far the ladder is from the foot of the wall. Ans.3.464 m Ans.exp.: We will use trigonmetry to solve the problem easily and quickly. Here AB represents height of the wall, BC represents the distance between the wall and the foot of the ladder and AC represents the length of the ladder. In the right triangle ABC, the side which is opposite to angle 60 degree is known as opposite side (AB), the side which is opposite to 90 degree is called hypotenuse side (AC) and remaining side is called adjacent side (BC). Now, we need to find the distance between foot of the ladder and the wall. That is, we have to find the length of BC.

I have opened the file in python and assigned the lines as follows:

 with open('Maths.txt') as f:

        lines = f.read().split('\n')

How should I proceeed further?

See e.g https://stackoverflow.com/questions/4710067/using-python-for-deleting-a-specific-line-in-a-file — Fredrik Pihl, Aug 21 '20 at 09:46
When you think about lines you think about sentences or do you think about actual lines (with newline character)? — Alex Baranowski, Aug 21 '20 at 09:48
as explained in the linked answer. Open the file, read the lines, then write back the desired ones. using enumerate for line-numbers or using `in` if matching a string — Fredrik Pihl, Aug 21 '20 at 09:53

score 0 · Answer 1 · answered Aug 21 '20 at 09:51

0

You'd better use readlines() in that purpose. Because read() method returns your text as a single big string, so you can't distinguish your lines. Using readlines() method, you'll get a list of lines.

You'll then just have to delete the unwanted lines in your list, then send the lines to another text file with f.writelines().

answered Aug 21 '20 at 09:51

S_Crespo

305
1
9

How can I delete a list of unwanted lines in a range for example line no.3 to 5? – Anubhab Das Aug 21 '20 at 09:54

score 0 · Answer 2 · answered Aug 21 '20 at 10:31

0

Maybe you can do something like this:

first_lines=f.read().split('\n')[:1]
last_lines=f.read().split('\n')[3:]

print(first_lines + last_lines)

I don't know if there is a way to do it directly.

answered Aug 21 '20 at 10:31

Kev Rob

322
2
7

How to delete specific lines from a text file in python

2 Answers2