Develop Reference

Python changing Comma Delimitation CSV

NEWBIE USING PYTHON (2.7.9)- When I export a gzipped file to a csv using:
myData = gzip.open('file.gz.DONE', 'rb')
myFile = open('output.csv', 'wb') with myFile:
writer = csv.writer(myFile)
writer.writerows(myData)
print("Writing complete")
It is printing in the csv with a comma deliminated in every character. eg.
S,V,R,","2,1,4,0,",",2,0,1,6,1,1,3,8,0,4,",",5,0,5,0,1,3,4,2,0,6,4,7,3,6,4,",",",",2,0,0,0,5,6,5,9,2,9,6,7,4,",",2,0,0,7,2,4,5,2,3,5,",",0,0,0,2,","
I,V,E,",",",",",",E,N,",",N,/,A,",",0,4,2,1,4,4,9,3,7,0,",":,I,R,_,",",N,/,A,",",U,N,A,N,S,W,",",",",",",",","
"
S,V,R,",",4,7,3,3,5,5,",",2,0,5,7,",",5,0,5,0,1,4,5,0,1,6,4,8,6,3,7,",",",",2,0,0,0,5,5,3,9,2,9,2,8,0,",",2,0,4,4,1,0,8,3,7,8,",",0,0,0,2,","
I,V,E,",",",",",",E,N,",",N,/,A,",",0,4,4,7,3,3,5,4,5,5,",",,:,I,R,_,",",N,/,A,",",U,N,A,N,S,W,",",",",",",",","
How do I get rid of the comma so that it is exported with the correct fields? eg.
SVR,2144370,20161804,50501342364,,565929674,2007245235,0002,1,PPDAP,PPLUS,DEACTIVE,,,EN,N/A,214370,:IR_,N/A,,,,,
SVR,473455,208082557,14501648637,,2000553929280,2044108378,0002,1,3G,CODAP,INACTIVE,,,EN,N/A,35455,:IR_,N/A,,,,,

You are only opening the gzip file. I think you are expecting the opened file to act automatically like an iterator. Which it does. However each line is a text string. The writerows expects an iterator with each item being an array of values to write with comma separation. Thus given an iterator with each item being a sting, and given that a string is an array of characters you get the result you found.
Since you didn't mention what the gzip data lines really contain I can't guess how to parse the lines into an array of reasonable chunks. But assuming a function called 'split_line' appropriate to that data you could do
with gzip.open('file.gz.Done', 'rb') as gzip_f:
data = [split_line(l) for l in gzip_f]
with open('output.csv', 'wb') as myFile:
writer = csv.writer(myFile)
writer.writerows(data)
print("Writing complete")
Of course at this point doing row by row and putting the with lines together makes sense.
See https://docs.python.org/2/library/csv.html

I think it's simply because gzip.open() will give you a file-like object but csvwriter.writerows() needs a list of lists of strings to do its work.
But I don't understand why you want to use the csv module. You look like you only want to extract the content of the gzip file and save it in a output file uncompressed. You could do that like that:
import gzip
input_file_name = 'file.gz.DONE'
output_file_name = 'output.csv'
with gzip.open(input_file_name, 'rt') as input_file:
with open('output.csv', 'wt') as output_file:
for line in input_file:
output_file.write(line)
print("Writing complete")
If you want to use the csv module because you're not sure your input data is properly formatted (and you want an error message right away) you could then do:
import gzip
import csv
input_file_name = 'file.gz.DONE'
output_file_name = 'output.csv'
with gzip.open(input_file_name, 'rt', newline='') as input_file:
reader_csv = csv.reader(input_file)
with open('output.csv', 'wt', newline='') as output_file:
writer_csv = csv.writer(output_file)
writer_csv.writerows(reader_csv)
print("Writing complete")
Is that what you were trying to do ? It's difficult to guess because we don't have the input file to understand.
If it's not what you want, could you care to clarify what you want?

Since I now have information the gzipped file is itself comma, separated values it simplifies thus..
with gzip.open('file.gz.DONE', 'rb') as gzip_f, open('output.csv', 'wb') as myFile:
myfile.write(gzip_f.read())
In other words it is just a round about gunzip to another file.

Appending characters to each line in a txt file with python

I wrote the following python code snippet to append a lower p character to each line of a txt file:
f = open('helloworld.txt','r')
for line in f:
line+='p'
print(f.read())
f.close()
However, when I execute this python program, it returns nothing but an empty blank:
zhiwei#zhiwei-Lenovo-Rescuer-15ISK:~/Documents/1001/ass5$ python3 helloworld.py
Can anyone tell me what's wrong with my codes?

Currently, you are only reading each line and not writing to the file. reopen the file in write mode and write your full string to it, like so:
newf=""
with open('helloworld.txt','r') as f:
for line in f:
newf+=line.strip()+"p\n"
f.close()
with open('helloworld.txt','w') as f:
f.write(newf)
f.close()

well, type help(f) in shell, you can get "Character and line based layer over a BufferedIOBase object, buffer."
it's meaning：if you reading first buffer,you can get content, but again. it's empty。
so like this:
with open(oldfile, 'r') as f1, open(newfile, 'w') as f2:
newline = ''
for line in f1:
newline+=line.strip()+"p\n"
f2.write(newline)

open(filePath, openMode) takes two arguments, the first one is the path to your file, the second one is the mode it will be opened it. When you use 'r' as second argument, you are actually telling Python to open it as an only reading file.
If you want to write on it, you need to open it in writing mode, using 'w' as second argument. You can find more about how to read/write files in Python in its official documentation.
If you want to read and write at the same time, you have to open the file in both reading and writing modes. You can do this simply by using 'r+' mode.

It seems that your for loop has already read the file to the end, so f.read() return empty string.
If you just need to print the lines in the file, you could move the print into for loop just like print(line). And it is better to move the f.read() before for loop:
f = open("filename", "r")
lines = f.readlines()
for line in lines:
line += "p"
print(line)
f.close()
If you need to modify the file, you need to create another file obj and open it in mode of "w", and use f.write(line) to write the modified lines into the new file.
Besides, it is more better to use with clause in python instead of open(), it is more pythonic.
with open("filename", "r") as f:
lines = f.readlines()
for line in lines:
line += "p"
print(line)
When using with clause, you have no need to close file, this is more simple.

How to read file first line and write from the second

I have a file and I would like to read the first line and write from the second.
with open(file_path, 'r+') as f:
f.readline()
for values in my_array:
f.write("%s=%s" % (str(values[0]), str(values[1])))
Any suggestion?

You can't write on a file while reading it.
Two solutions :
Have a second file where you rewrite your first line and then write the second one :
with open(file_path, 'r+') as f:
line = f.readline()
with open('another_file.txt', 'w') as outfile:
outfile.write(line)
outfile.write(...) # Whatever you want on your second line
Store everything you want to write in memory and then write over your previous file (Which I don't recommend, if something happens midway and your file is stil overwritten, all previous data will be lost).

Store and recall a variable in a text file Python

How would i store the variable x on a specific line (the first)in a text file and recover it as the program opens.
Also how would i store data in a text file on a specific line

You should take a look at the open() built-in.
#To write to a file:
with open("file.txt", "w") as f:
f.write("Data!")
#To read from a file:
with open("file.txt", "r") as f:
print(f.read())
Next time, you should check for duplicates:
easy save/load of data in python, Writing a Top Score to a data file.

Replace a word in a file

I am new to Python programming...
I have a .txt file....... It looks like..
0,Salary,14000
0,Bonus,5000
0,gift,6000
I want to to replace the first '0' value to '1' in each line. How can I do this? Any one can help me.... With sample code..
Thanks in advance.
Nimmyliji

I know that you're asking about Python, but forgive me for suggesting that perhaps a different tool is better for the job. :) It's a one-liner via sed:
sed 's/^0,/1,/' yourtextfile.txt > output.txt
This applies the regex /^0,/ (which matches any 0, that occurs at the beginning of a line) to each line and replaces the matched text with 1, instead. The output is directed into the file output.txt specified.

inFile = open("old.txt", "r")
outFile = open("new.txt", "w")
for line in inFile:
outFile.write(",".join(["1"] + (line.split(","))[1:]))
inFile.close()
outFile.close()
If you would like something more general, take a look to Python csv module. It contains utilities for processing comma-separated values (abbreviated as csv) in files. But it can work with arbitrary delimiter, not only comma. So as you sample is obviously a csv file, you can use it as follows:
import csv
reader = csv.reader(open("old.txt"))
writer = csv.writer(open("new.txt", "w"))
writer.writerows(["1"] + line[1:] for line in reader)
To overwrite original file with new one:
import os
os.remove("old.txt")
os.rename("new.txt", "old.txt")
I think that writing to new file and then renaming it is more fault-tolerant and less likely corrupt your data than direct overwriting of source file. Imagine, that your program raised an exception while source file was already read to memory and reopened for writing. So you would lose original data and your new data wouldn't be saved because of program crash. In my case, I only lose new data while preserving original.

o=open("output.txt","w")
for line in open("file"):
s=line.split(",")
s[0]="1"
o.write(','.join(s))
o.close()
Or you can use fileinput with in place edit
import fileinput
for line in fileinput.FileInput("file",inplace=1):
s=line.split(",")
s[0]="1"
print ','.join(s)

f = open(filepath,'r')
data = f.readlines()
f.close()
edited = []
for line in data:
edited.append( '1'+line[1:] )
f = open(filepath,'w')
f.writelines(edited)
f.flush()
f.close()
Or in Python 2.5+:
with open(filepath,'r') as f:
data = f.readlines()
with open(outfilepath, 'w') as f:
for line in data:
f.write( '1' + line[1:] )
This should do it. I wouldn't recommend it for a truly big file though ;-)
What is going on (ex 1):
1: Open the file in read mode
2,3: Read all the lines into a list (each line is a separate index) and close the file.
4,5,6: Iterate over the list constructing a new list where each line has the first character replaced by a 1. The line[1:] slices the string from index 1 onward. We concatenate the 1 with the truncated list.
7,8,9: Reopen the file in write mode, write the list to the file (overwrite), flush the buffer, and close the file handle.
In Ex. 2:
I use the with statement that lets the file handle closing itself, but do essentially the same thing.