CODEWITHSUNDEEP
python
gdogg371
gdogg371

Reputation: 4122

IOError: File not open for writing - Python

I am opening a file and if a particular condition is met, opening another file and transferring the records from the first file to the second, then deleting them from the first. The code below works, except for the line f.truncate(), which is causing the error in this post's title. Can anyone tell me what I need to amend to make this work?

f = open(filename,"r")
d = f.readlines()
f.seek(0)
for i in d:
    e = i.split(',')
    if len(e) > 28:
        with open(filename2, "a") as text_file:
            text_file.write(i.encode('cp1252'))
        text_file.close
f.truncate()        
f.close()

Upvotes: 1

Views: 5433

Answers (2)

alexis
alexis

Reputation: 50180

Think of it as reading file1, splitting it in two, and writing the parts to file1 and file2. I wouldn't even bother with truncate() since opening a file for writing truncates it:

with open(filename1) as file1:
    data = file1.readlines()

lines1 = []
lines2 = []
for line in data:
    if len(line.split(",")) > 28:
        lines2.append(line)
    else:
        lines1.append(line)

with open(filename1, "w", encoding='cp1252') as outfile:   # Wipes out old contents
    outfile.writelines(lines1)

with open(filename2, "w", encoding='cp1252') as outfile: 
    outfile.writelines(lines2)

Upvotes: 0

Bharel
Bharel

Reputation: 26901

You have to open the first file as "r+" in order to read and write, like so:

f = open(filename,"r+")
for line in f:
    e = line.split(',')
    if len(e) > 28:
        with open(filename2, "a") as text_file:
            text_file.write(line.encode('cp1252'))
f.seek(0)
f.truncate()        
f.close()

I have also made the code more efficient as it should iterate over the lines instead of copying them to the side. An even more efficient approach would be this:

with open(filename,"r+") as file1, open(filename2, "a") as file2:
    for line in f:
        if line.count(',') > 27:
            file2.write(line.encode('cp1252'))
    file1.truncate(0)

That way you don't reopen the file every iteration, and since you're not using the split values, you can just count the commas (,) and compare to 27 instead of 28.

Removing only the copied lines

If you wish to remove only the copied lines and not empty the file, you have no way other than copying the entire file to the memory or using a tempfile.

That's the way to do it by copying to memory:

with open(filename,"r+") as file1, open(filename2, "a") as file2:
    file_lines = file1.readlines()
    file1.seek(0)
    file1.truncate()
    for line in file_lines:
        if line.count(',') > 27:
            file2.write(line.encode('cp1252'))
        else:
            file1.write(line)

Please make sure to specify an encoding if you're using Python 3.X.

Upvotes: 4

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