I am trying to write to a csv file that has been saved with another program (excel and others).
However when I open the file to write to it, the first line written is added to last cell of the last line.
file.csv
['1','2','3']
['1','2','3']
import csv
fields=['A','B','C']
with open('file.csv', 'a', newline='') as f:
writer = csv.writer(f)
writer.writerow(fields)
Expected results:
['1','2','3']
['1','2','3']
['A','B','C']
Actual results:
['1','2','3']
['1','2','3A','B','C']
If I just write to file then write to it again without viewing it, there's no issue, but if I open the file, and save it inside the program the next line written is added to the previous line instead of becoming it's own line.
I assume there is a formatting issue with how the program saves the file, but I am at a loss as to how to fix it.
Lines in CSV files should always be terminated with a "\r\n" sequence, even if its the last line in the file. In the grand tradition of CSV programming, this is often ignored. The fix is to write a program that peeks at the file and fixes it as needed before use. And write a bug against the "other" program that wrote the nonconforming CSV in the first place.
import csv
def csv_delimiter_fixer(filename):
with open(filename, 'a+b') as fileobj:
fileobj.seek(-1, 2)
if fileobj.read(1) != b"\n":
fileobj.write(b"\r\n")
fields=['A','B','C']
filename = 'file.csv'
csv_delimiter_fixer(filename)
with open('file.csv', 'a', newline='') as f:
writer = csv.writer(f)
writer.writerow(fields)
Related
I wanted to read some input from the csv file and then modify the input and replace it with the new value. For this purpose, I first read the value but then I'm stuck at this point as I want to modify all the values present in the file.
So is it possible to open the file in r mode in one for loop and then immediately in w mode in another loop to enter the modified data?
If there is a simpler way to do this please help me out
Thank you.
Yes, you can open the same file in different modes in the same program. Just be sure not to do it at the same time. For example, this is perfectly valid:
with open("data.csv") as f:
# read data into a data structure (list, dictionary, etc.)
# process lines here if you can do it line by line
# process data here as needed (replacing your values etc.)
# now open the same filename again for writing
# the main thing is that the file has been previously closed
# (after the previous `with` block finishes, python will auto close the file)
with open("data.csv", "w") as f:
# write to f here
As others have pointed out in the comments, reading and writing on the same file handle at the same time is generally a bad idea and won't work as you expect (unless for some very specific use case).
You can do open("data.csv", "rw"), this allows you to read and write at the same time.
Just like others have mentioned, modifying the same file as both input and output without any backup method is such a terrible idea, especially in a condensed file like most .csv files, which is normally more complicated than a single .Txt based file, but if you insisted you can do with the following:
import csv
file path = 'some.csv'
with open('some.csv', 'rw', newline='') as csvfile:
read_file = csv.reader(csvfile)
write_file = csv.writer(csvfile)
Note that code above will trigger an error with a message ValueError: must have exactly one of create/read/write/append mode.
For safety, I preferred to split it into two different files
import csv
in_path = 'some.csv'
out_path = 'Out.csv'
with open(in_path, 'r', newline='') as inputFile, open(out_path, 'w', newline='') as writerFile:
read_file = csv.reader(inputFile)
write_file = csv.writer(writerFile, delimiter=' ', quotechar='|', quoting=csv.QUOTE_MINIMAL)
for row in read_file:
# your modifying input data code here
........
i need to read a csv file and translate it in uppercase and store it in another csv file with python
I have this code:
import csv
with open('data_csv.csv', 'rb') as f:
header = next(f).strip().split(',')
reader = csv.DictReader((l.upper() for l in f), fieldnames=header)
for line in reader:
print line
with open('test.csv', 'r') as f:
for line in f:
print line
but I can not find the right result
You don't need to read the header separately. If you don't provide a fieldnames argument to DictReader(), the header is read automatically. Next, don't print your lines, you have now read the whole file and dropped all the lines.
Open both the input and output files in the same with statement, you can then write lines directly to the output. There is no need to use the csv module here, because you don't need to parse out the rows, then form the rows into lines again.
Just loop over the file, uppercase the lines, and write out the result:
with open('data_csv.csv', 'r') as input, open('test.csv', 'w') as output:
output.writelines(line.upper() for line in input)
My situation is, I have csv file and here is its code.
user_file = Path(str(message.author.id) + '.cvs')
if user_file.exists():
with open('test.csv', 'a') as fp:
writer = csv.writer(fp, delimiter=',')
writer.writerows(data)
else:
with open(user_file, 'w') as fp:
data = [('xp', 0)]
writer = csv.writer(fp, delimiter=',')
writer.writerows(data)
I'm wanting a csv file that keeps track of how many times they type a message so i need a way of editing the csv file and adding 1 to what it already has. But i have no idea how to do that! please help!<3
test.csv:
4
Python:
# Replace test.csv with the file you wish to open. Keep "w+"
with open("test.csv", "w+") as dat:
# Assumes the text in the file is an int
n = int(dat.read())
dat.write(str(n+1))
Result in test.csv:
5
This way it opens the file as write and read, reads the number, then writes it back as a string. Note that write() will override any text in the current file, so you don't need to remove the text
P.S if that if else statement is to check the file actually exists, it's unnecessary. If you try to open() a file which doesn't exist, python will create it for you.
I'm attempting to rewrite specific cells in a csv file using Python.
However, whenever I try to modify an aspect of the csv file, the csv file ends up being emptied (the file contents becomes blank).
Minimal code example:
import csv
ReadFile = open("./Resources/File.csv", "rt", encoding = "utf-8-sig")
Reader = csv.reader(ReadFile)
WriteFile = open("./Resources/File.csv", "wt", encoding = "utf-8-sig")
Writer = csv.writer(WriteFile)
for row in Reader:
row[3] = 4
Writer.writerow(row)
ReadFile.close()
WriteFile.close()
'File.csv' looks like this:
1,2,3,FOUR,5
1,2,3,FOUR,5
1,2,3,FOUR,5
1,2,3,FOUR,5
1,2,3,FOUR,5
In this example, I'm attempting to change 'FOUR' to '4'.
Upon running this code, the csv file becomes empty instead.
So far, the only other question related to this that I've managed to find is this one, which does not seem to be dealing with rewriting specific cells in a csv file but instead deals with writing new rows to a csv file.
I'd be very grateful for any help anyone reading this could provide.
The following should work:
import csv
with open("./Resources/File.csv", "rt", encoding = "utf-8-sig") as ReadFile:
lines = list(csv.reader(ReadFile))
with open("./Resources/File.csv", "wt", encoding = "utf-8-sig") as WriteFile:
Writer = csv.writer(WriteFile)
for line in lines:
line[3] = 4
Writer.writerow(line)
When you open a writer with w option, it will delete the contents and start writing the file anew. The file is therefore, at the point when you start to read, empty.
Try writing to another file (like FileTemp.csv) and at the end of the program renaming FileTemp.csv to File.csv.
I'm new to python.
I have a list with 19188 rows that I want to save as a csv.
When I write the list's rows to the csv, it does not have the last rows (it stops at 19112).
Do you have any idea what might cause this?
Here is how I write to the csv:
mycsvfile = open('file.csv', 'w')
thedatawriter = csv.writer(mycsvfile, lineterminator = '\n')
list = []
#list creation code
thedatawriter.writerows(list)
Each row of list has 4 string elements.
Another piece of information:
If I create a list that contains only the last elements that are missing and add them to the csv file, it kind of works (it is added, but twice...).
mycsvfile = open('file.csv', 'w')
thedatawriter = csv.writer(mycsvfile, lineterminator = '\n')
list = []
#list creation code
thedatawriter.writerows(list)
list_end = []
#list_end creation code
thedatawriter.writerows(list_end)
If I try to add the list_end alone, it doesn't seem to be working. I'm thinking there might be a csv writing parameter that I got wrong.
Another piece of information:
If I open the file adding ", newline=''", then it write more rows to it (though not all)
mycsvfile = open('file.csv', 'w', newline='')
There must be a simple mistake in the way I open or write to the csv (or in the dialect?)
Thanks for your help!
I found my answer! I was not closing the filehandle before script end which left unwritten rows.
Here is the fix:
with open('file.csv', 'w', newline='') as mycsvfile:
thedatawriter = csv.writer(mycsvfile, lineterminator = '\n')
thedatawriter.writerows(list)
See: Writing to CSV from list, write.row seems to stop in a strange place
Close the filehandle before the script ends. Closing the filehandle
will also flush any strings waiting to be written. If you don't flush
and the script ends, some output may never get written.
Using the with open(...) as f syntax is useful because it will close
the file for you when Python leaves the with-suite. With with, you'll
never omit closing a file again.