I have an XML file that contains an illegal character, I am iterating through the file, removing the character from all of the lines and storing the lines in a list. I now want to write those same lines back into the file and overwrite what is already there.
I tried this:
file = open(filename, "r+")
#do stuff
Which is only appending the results to the end of the file, I would like to overwrite the existing file.
And this:
file = open(filename, "r")
#read from the file
file.close()
file = open(filename, "w")
#write to file
file.close()
This gives me a Bad File Descriptor error.
How can i read and write to the same file?
Thanks
You could re-write the lines list with writelines function.
with open(filename, "r") as f:
lines = f.readlines()
#edit lines here
with open(filename, "w") as f:
f.writelines(lines)
The reason you're appending to the end of the file the whole time is that you need to seek to the beginning of the file to write your lines out.
with open(filename, "r+") as file:
lines = file.readlines()
lines = [line.replace(bad_character, '') for line in lines]
file.seek(0)
file.writelines(lines)
file.truncate() # Will get rid of any excess characters left at the end of the file due to the length of your new file being shorter than the old one, as you've removed characters.
(Decided to just use the context manager syntax myself.)
Related
iam using this code to to pull the first line at text file at threading mod before delete it from the file
with open(r'C:\datanames\names.txt','r') as fin:
name = fin.readline()
with open(r'C:\datanames\names.txt', 'r') as fin:
data = fin.read().splitlines(True)
with open(r'C:\datanames\names.txt', 'w') as fout:
fout.writelines(data[1:])
put it make me lose the data Often
Is there a more efficient and practical way to use it in such a situation? (threading)
I see no reason to use threading for this. It's very straightforward.
To remove the first line from a file do this:
FILENAME = 'foo.txt'
with open(FILENAME, 'r+') as file:
lines = file.readlines()
file.seek(0)
file.writelines(lines[1:])
file.truncate()
I have 1000 files, and the name of these are "numbers", for example, 2323.csv.
I have these name in a file called 1.txt.
Now I want to open these files one by one in python, using 1.txt to open them.
How can I do this?
Why not this?
with open('1.txt', 'r') as listFile:
for line in listFile:
with open(line.rstrip(), 'r') as individualFile:
# do stuff
Roughly and very basic but understandable code (no error handling).
with open('1.txt', 'r') as f:
for line in f.readlines(): # This assumes each line has a number
with open('.'.join([line, 'csv']) as cf:
file_content = cf.readlines()
print(file_content)
I have about 4000 txt files in a directory. I'd like to replace newlines with spaces in each file using a for loop. Actually, the script works for that purpose but when I save the file, it doesn't get saved or it gets saved with newlines again. Here is my script;
import glob
path = "path_to_files/*.txt"
for file in glob.glob(path):
with open(file, "r+") as f:
data = f.read().replace('\n', ' ')
f.write(data)
As I said I'm able to replace the newlines with a space, but at the end, it doesn't get saved. I also don't get any errors.
To further elaborate my comment ("It's almost always a bad idea to open a file in the 'r+' mode (because of the way the current position is handled). Open a file for reading, read the data, replace the newlines, open the same file file for writing, write the data"):
for file in glob.glob(path):
with open(file) as f:
data = f.read().replace('\n', ' ')
with open(file, "w") as f:
f.write(data)
You need to reset file position to 0 with seek and then truncate the leftover with truncate after you finishing writing the replacement string.
import glob
path = "path_to_files/*.txt"
for file in glob.glob(path):
with open(file, "r+") as f:
data = f.read().replace('\n', ' ')
f.seek(0)
f.write(data)
f.truncate()
The context is the following one, I have two text file that I need to edit.
I open the first text file read it line by line and edit it but sometimes when I encounter a specific line in the first text file I need to overwritte content of the the second file.
However, each time I re-open the second text file instead of overwritting its content the below code appends it to the file...
Thanks in advance.
def edit_custom_class(custom_class_path, my_message):
with open(custom_class_path, "r+") as file:
file.seek(0)
for line in file:
if(some_condition):
file.write(mu_message)
def process_file(file_path):
with open(file_path, "r+") as file:
for line in file:
if(some_condition):
edit_custom_class(custom_class_path, my_message)
In my opinion, simultaneously reading and modifying a file is a bad thing to do. Consider using something like this. First read the file, make modifications, and then overwrite the file completely.
def modify(path):
out = []
f = open(path)
for line in f:
if some_condition:
out.append(edited_line) #make sure it has a \n at the end
else:
out.append(original_line)
f.close()
with open(path,'w') as f:
for line in out:
f.write(line)
I am trying to form a quotes file of a specific user name in a log file. How do I remove every line that does not contain the specific user name in it? Or how do I write all the lines which contain this user name to a new file?
with open('input.txt', 'r') as rfp:
with open('output.txt', 'w') as wfp:
for line in rfp:
if ilikethis(line):
wfp.write(line)
with open(logfile) as f_in:
lines = [l for l in f_in if username in l]
with open(outfile, 'w') as f_out:
f_out.writelines(lines)
Or if you don't want to store all the lines in memory
with open(logfile) as f_in:
lines = (l for l in f_in if username in l)
with open(outfile, 'w') as f_out:
f_out.writelines(lines)
I sort of like the first one better but for a large file, it might drag.
Something along this line should suffice:
newfile = open(newfilename, 'w')
for line in file(filename, 'r'):
if name in line:
newfile.write(line)
newfile.close()
See : http://docs.python.org/tutorial/inputoutput.html#methods-of-file-objects
f.readlines() returns a list containing all the lines of data in the file.
An alternative approach to reading lines is to loop over the file object. This is memory efficient, fast, and leads to simpler code
>>> for line in f:
print line
Also you can checkout the use of with keyword. The advantage that the file is properly closed after its suite finishes
>>> with open(filename, 'r') as f:
... read_data = f.read()
>>> f.closed
True
I know you asked for python, but if you're on unix this is a job for grep.
grep name file
If you're not on unix, well... the answer above does the trick :)