def read_slice():
openfile=open('slicefile1.txt','r')
#savetofile=open('slicefile2.txt','w')
lines = openfile.readlines()
for line in lines:
line.slice(',')[16].split('\t')
print(line)
The file that I want to read and parse ( is that the correct word?) is in the format
['05,21,34,37,38,01,06', '09,16,26,36,39,02,06', '03,10,18,31,37,02,04'].
I want to return ( actually write to another file) in the format
05,21,34,37,38 tab 01,06
09,16,26,36,39 tab 02,06
I am obviously stupid because I still cannot handle lists and strings. The function gives an error method slice not available of string. Please help if you would
Slicing in python strings refers to using the [start:stop:step] notation. In your case, you can simply use:
'\t'.join((line[:14], line[15:]))
to split the line and rejoin it with a tab:
>>> line = '05,21,34,37,38,01,06'
>>> line[:14]
'05,21,34,37,38'
>>> line[15:]
'01,06'
>>> '\t'.join((line[:14], line[15:]))
'05,21,34,37,38\t01,06'
Slightly more complicated that Martijn's answer, but perhaps more flexible if changes to formatting or delimiters etc... occur:
import csv
with open('yourfile') as fin, open('output.csv', 'wb') as fout:
csvin = csv.reader(fin)
csvout = csv.writer(fout, delimiter='\t')
for row in csvin:
csvout.writerow( [','.join(row[:5], ','.join(row[5:])] )
Related
I have a file saved as .csv
"400":0.1,"401":0.2,"402":0.3
Ultimately I want to save the data in a proper format in a csv file for further processing. The problem is that there are no line breaks in the file.
pathname = r"C:\pathtofile\file.csv"
with open(pathname, newline='') as file:
reader = file.read().replace(',', '\n')
print(reader)
with open(r"C:\pathtofile\filenew.csv", 'w') as new_file:
csv_writer = csv.writer(new_file)
csv_writer.writerow(reader)
The print reader output looks exactly how I want (or at least it's a format I can further process).
"400":0.1
"401":0.2
"402":0.3
And now I want to save that to a new csv file. However the output looks like
"""",4,0,0,"""",:,0,.,1,"
","""",4,0,1,"""",:,0,.,2,"
","""",4,0,2,"""",:,0,.,3
I'm sure it would be intelligent to convert the format to
400,0.1
401,0.2
402,0.3
at this stage instead of doing later with another script.
The main problem is that my current code
with open(pathname, newline='') as file:
reader = file.read().replace(',', '\n')
reader = csv.reader(reader,delimiter=':')
x = []
y = []
print(reader)
for row in reader:
x.append( float(row[0]) )
y.append( float(row[1]) )
print(x)
print(y)
works fine for the type of csv files I currently have, but doesn't work for these mentioned above:
y.append( float(row[1]) )
IndexError: list index out of range
So I'm trying to find a way to work with them too. I think I'm missing something obvious as I imagine that it can't be too hard to properly define the linebreak character and delimiter of a file.
with open(pathname, newline=',') as file:
yields
ValueError: illegal newline value: ,
The right way with csv module, without replacing and casting to float:
import csv
with open('file.csv', 'r') as f, open('filenew.csv', 'w', newline='') as out:
reader = csv.reader(f)
writer = csv.writer(out, quotechar=None)
for r in reader:
for i in r:
writer.writerow(i.split(':'))
The resulting filenew.csv contents (according to your "intelligent" condition):
400,0.1
401,0.2
402,0.3
Nuances:
csv.reader and csv.writer objects treat comma , as default delimiter (no need to file.read().replace(',', '\n'))
quotechar=None is specified for csv.writer object to eliminate double quotes around the values being saved
You need to split the values to form a list to represent a row. Presently the code is splitting the string into individual characters to represent the row.
pathname = r"C:\pathtofile\file.csv"
with open(pathname) as old_file:
with open(r"C:\pathtofile\filenew.csv", 'w') as new_file:
csv_writer = csv.writer(new_file, delimiter=',')
text_rows = old_file.read().split(",")
for row in text_rows:
items = row.split(":")
csv_writer.writerow([int(items[0]), items[1])
If you look at the documentation, for write_row, it says:
Write the row parameter to the writer’s file
object, formatted according to the current dialect.
But, you are writing an entire string in your code
csv_writer.writerow(reader)
because reader is a string at this point.
Now, the format you want to use in your CSV file is not clearly mentioned in the question. But as you said, if you can do some preprocessing to create a list of lists and pass each sublist to writerow(), you should be able to produce the required file format.
I have a .csv file with many lines and with the structure:
YYY-MM-DD HH first_name quantity_number second_name first_number second_number third_number
I have a script in python to convert the separator from space to comma, and that working fine.
import csv
with open('file.csv') as infile, open('newfile.dat', 'w') as outfile:
for line in infile:
outfile.write(" ".join(line.split()).replace(' ', ','))
I need change, in the newfile.dat, the position of each value, for example put the HH value in position 6, the second_name value in position 2, etc.
Thanks in advance for your help.
If you're import csv might as well use it
import csv
with open('file.csv', newline='') as infile, open('newfile.dat', 'w+', newline='') as outfile:
read = csv.reader(infile, delimiter=' ')
write = csv.writer(outfile) #defaults to excel format, ie commas
for line in read:
write.writerow(line)
Use newline='' when opening csv files, otherwise you get double spaced files.
This just writes the line as it is in the input. If you want to change it before writing, do it in the for line in read: loop. line is a list of strings, which you can change the order of in any number of ways.
One way to reorder the values is to use operator.itemgetter:
from operator import itemgetter
getter = itemgetter(5,4,3,2,1,0) #This will reverse a six_element list
for line in read:
write.writerow(getter(line))
To reorder the items, a basic way could be as follows:
split_line = line.split(" ")
column_mapping = [9,6,3,7,3,2,1]
reordered = [split_line[c] for c in column_mapping]
joined = ",".join(reordered)
outfile.write(joined)
This splits up the string, reorders it according to column_mapping and then combines it back into one string (comma separated)
(in your code don't include column_mapping in the loop to avoid reinitialising it)
I am receiving a error on this code. It is "TypeError: expected string or buffer". I looked around, and found out that the error is because I am passing re.sub a list, and it does not take lists. However, I wasn't able to figure out how to change my line from the csv file into something that it would read.
I am trying to change all the periods in a csv file into commas. Here is my code:
import csv
import re
in_file = open("/test.csv", "rb")
reader = csv.reader(in_file)
out_file = open("/out.csv", "wb")
writer = csv.writer(out_file)
for row in reader:
newrow = re.sub(r"(\.)+", ",", row)
writer.writerow(newrow)
in_file.close()
out_file.close()
I'm sorry if this has already been answered somewhere. There was certainly a lot of answers regarding this error, but I couldn't make any of them work with my csv file. Also, as a side note, this was originally an .xslb excel file that I converted into csv in order to be able to work with it. Was that necessary?
You could use list comprehension to apply your substitution to each item in row
for row in reader:
newrow = [re.sub(r"(\.)+", ",", item) for item in row]
writer.writerow(newrow)
for row in reader does not return single element to parse it rather it returns list of of elements in that row so you have to unpack that list and parse each item individually, just like #Trii shew you:
[re.sub(r'(\.)+','.',s) for s in row]
In this case, we are using glob to access all the csv files in the directory.
The code below overwrites the source csv file, so there is no need to create an output file.
NOTE:
If you want to get a second file with the parameters provided with re.sub, replace write = open(i, 'w') for write = open('secondFile.csv', 'w')
import re
import glob
for i in glob.glob("*.csv"):
read = open(i, 'r')
reader = read.read()
csvRe = re.sub(re.sub(r"(\.)+", ",", str(reader))
write = open(i, 'w')
write.write(csvRe)
read.close()
write.close()
I'm having some problems with the following file.
Each line has the following content:
foobar 1234.569 7890.125 12356.789 -236.4569 236.9874 -569.9844
What I want to edit in this file, is reverse last three numbers, positive or negative.
The output should be:
foobar 1234.569 7890.125 12356.789 236.4569 -236.9874 569.9844
Or even better:
foobar,1234.569,7890.125,12356.789,236.4569,-236.9874,569.9844
What is the easiest pythonic way to accomplish this?
At first I used the csv.reader, but I found out it's not tab separated, but random (3-5) spaces.
I've read the CSV module and some examples / similar questions here, but my knowledge of python ain't that good and the CSV module seems pretty tough when you want to edit a value of a row.
I can import and edit this in excel with no problem, but I want to use it in a python script, since I have hundreds of these files. VBA in excel is not an option.
Would it be better to just regex each line?
If so, can someone point me in a direction with an example?
You can use str.split() to split your white-space-separated lines into a row:
row = line.split()
then use csv.writer() to create your new file.
str.split() with no arguments, or None as the first argument, splits on arbitrary-width whitespace and ignores leading and trailing whitespace on the line:
>>> 'foobar 1234.569 7890.125 12356.789 -236.4569 236.9874 -569.9844\n'.split()
['foobar', '1234.569', '7890.125', '12356.789', '-236.4569', '236.9874', '-569.9844']
As a complete script:
import csv
with open(inputfilename, 'r') as infile, open(outputcsv, 'wb') as outfile:
writer = csv.writer(outfile)
for line in infile:
row = line.split()
inverted_nums = [-float(val) for val in row[-3:]]
writer.writerow(row[:-3] + inverted_nums)
from operator import neg
with open('file.txt') as f:
for line in f:
line = line.rstrip().split()
last3 = map(str,map(neg,map(float,line[-3:])))
print("{0},{1}".format(line[0],','.join(line[1:-3]+last3)))
Produces:
>>>
foobar,1234.569,7890.125,12356.789,236.4569,-236.9874,569.9844
CSV outputting version:
with open('file.txt') as f, open('ofile.txt','w+') as o:
writer = csv.writer(o)
for line in f:
line = line.rstrip().split()
last3 = map(neg,map(float,line[-3:]))
writer.writerow(line[:-3]+last3)
You could use genfromtxt:
import numpy as np
a=np.genfromtxt('foo.csv', dtype=None)
with open('foo.csv','w') as f:
for el in a[()]:
f.write(str(el)+',')
I'm trying to remove the last row in a csv but I getting an error: _csv.Error: string with NUL byte
This is what I have so far:
dcsv = open('PnL.csv' , 'a+r+b')
cWriter = csv.writer(dcsv, delimiter=' ')
cReader = csv.reader(dcsv)
for row in cReader:
cWriter.writerow(row[:-1])
I cant figure out why I keep getting errors
I would just read in the whole file with readlines(), pop out the last row, and then write that with csv module
import csv
f = open("summary.csv", "r+w")
lines=f.readlines()
lines=lines[:-1]
cWriter = csv.writer(f, delimiter=',')
for line in lines:
cWriter.writerow(line)
This should work
import csv
f = open('Pnl.csv', "r+")
lines = f.readlines()
lines.pop()
f = open('Pnl.csv', "w+")
f.writelines(lines)
I'm not sure what you're doing with the 'a+r+b' file mode and reading and writing to the same file, so won't provide a complete code snippet, but here's a simple method to skip any lines that contains a NUL byte in them in a file you're reading, whether it's the last, first, or one in the middle being read.
The trick is to realize that the docs say the csvfile argument to a csv.writer() "can be any object which supports the iterator protocol and returns a string each time its next() method is called." This means that you can replace the file argument in the call with a simple filter iterator function defined this way:
def filter_nul_byte_lines(a_file):
for line in a_file:
if '\x00' not in line:
yield line
and use it in a way similar to this:
dcsv = open('Pnl.csv', 'rb+')
cReader = csv.reader(filter_nul_byte_lines(dcsv))
for row in cReader:
print row
This will cause any lines with a NUL byte in them to be ignored while reading the file. Also this technique works on-the-fly as each line is read, so it does not require reading the entire file into memory at once or preprocessing it ahead of time.