Reading a text file line by line, if the line contains a specific string I want to add that entire l-CodePudding

Reading a text file line by line, if the line contains a specific string I want to add that entire line a separate text file

# read in the file
file = open("/home/jimmy/python/test.txt", "r")

# create an empty list to hold the good lines
good_lines = []

# check each line of the file and filter which to keep

for num, line in file:
        if " A" in line:
            num = str(num)
            good_lines.append(num)

f = open("goodline.txt", "w")
f.write(str(good_lines))
f.close()


'''

Not sure what is wrong. I am also not totally sure how to use that specific type of for loop with the comma.

Error I'm getting is the for loop line

ValueError: too many values to unpack (expected 2)

CodePudding user response：

That is a lot of code for one task in which Python can be quite expressive.

In particular one can pass to a call to "writelines" in the output file a generator expression - a very handy nice construct which allows for mapping and filtering in a stream in a simple expression (and we don't even need mapping in this case).

open("output file.txt", "wt").writelines(
    line for line in open("input file.txt") 
        if " A" in line)
)

(Yes, that is all the code you need for this task, and will run as is: just replace the file names as needed)

CodePudding user response：

In testing out your code and doing some tweaks, you might try out this code snippet.

# read in the file
test_file = open("test.txt", "r")   # You might change this to have an absolute path

# create an empty list to hold the good lines
good_lines = []

# check each line of the file and filter which to keep

for test_line in test_file:
    if " A" in test_line:
        good_lines.append(test_line)

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

for item in good_lines:
    f.write(str(item))
    
f.close()

The following was the text in the test file.

 A good line
 Another good line
Not a good line
Also not a good line

And this was the data in the created output file.

 A good line
 Another good line

Give that a try and see if it meets the spirit of your project.

CodePudding user response：

You can try the code below to see if it gets the correct output.

# read in the file
file = open("/home/jimmy/python/test.txt", "r")

# parses the lines in the text file
lines = file.readlines()

# create an empty list to hold the good lines
good_lines = []

# check each line of the file and filter which to keep

for line in lines:
        if " A" in line:
            num = str(line)
            good_lines.append(num)

f = open("goodline.txt", "w")
f.write(str(good_lines))
f.close()