Remove substring from a string in python

Question

I have got a file in python with filenames. I want to delete some lines and some substirng of the filename using python code. My file format is the above:

img/1.jpg
img/10.jpg
img/100.jpg 0 143 84 227
...

I want to delete the img/substring from all the file and the lines where the coordinates are missing. For the second task I did the following:

for con in content:
  if ".jpg\n" in con:
        content.remove(con)

for con in content:
    print con

However content didn't change.

Answer 1

You're attempting to modify the list content while iterating over it. This will very quickly bite you in the knees.

Instead, in python you generate a new list:

>>> content = [fn for fn in content if not fn.endswith(".jpg\n")]
>>> 

After this you can overwrite the file you read from with the contents from... contents . The above example assumes there is no whitespace to accomodate for in between the filename and the newline.

Answer 2

The error in your current method is because you are iterating through each line by letter , for l in somestring: will go letter by letter. Obviously, a ".jpg\\n" won't be in a single letter, so you never hit content.remove(con) .

I would suggest a slightly different approach:

with open("fileofdata.txt", 'r') as f:
    content = [line for line in f.readlines() if len(line.split()) > 1]

Using len(line.split()) is more robust than line.endswith() because it allows for withspace between .jpg and \\n .