Develop Reference

How to iterate through a directory of text files, pull specific lines, and write to a csv

Extremely novice coder here so please excuse my syntax errors.
My goal with this script is to:
Iterate through a directory of text files (text files are all the same format)
Pull values from specific lines in the text file (a subset of characters in the line)
Write these values to a common csv
My code is below. I'm having trouble getting this code to execute properly. I've tried to break it down into it's individual components to test, but I'm not having much luck. I'm having particular trouble trying to handle the nested indices to look at for ex/ line 41 and characters 3:6 of that line.
def main():
get_project_location()
get_file_variables()
for filename in path_txt_files:
with open(filename, 'r') as file:
for line in file.readlines():
with open('csv_output.csv', 'w+') as csv_output:
csv_writer = csv.writer(csv_output, delimiter=',')
csv_writer.writerow(line[41[3:6]])
csv_writer.writerow(line[121[3:6]])
close(filename)
def get_project_location():
return os.path.dirname(os.path.abspath(__file__))
def get_file_variables():
path_txt_files = os.path.join(
get_project_location(),
'txt_file_directory')

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.

Loop that will iterate a certain number of times through a CSV in Python

I have a large CSV file (~250000 rows) and before I work on fully parsing and sorting it I was trying to display only a part of it by writing it to a text file.
csvfile = open(file_path, "rb")
rows = csvfile.readlines()
text_file = open("output.txt", "w")
row_num = 0
while row_num < 20:
text_file.write(", ".join(row[row_num]))
row_num += 1
text_file.close()
I want to iterate through the CSV file and write only a small section of it to a text file so I can look at how it does this and see if it would be of any use to me. Currently the text file ends up empty.
A way I thought might do this would be to iterate through the file with a for loop that exits after a certain number of iteration but I could be wrong and I'm not sure how to do this, any ideas?

There's nothing specifically wrong with what you're doing, but it's not particularly Pythonic. In particular reading the whole file into memory with readlines() at the start seems pointless if you're only using 20 lines.
Instead you could use a for loop with enumerate and break when necessary.
csvfile = open(file_path, "rb")
text_file = open("output.txt", "w")
for i, row in enumerate(csvfile):
text_file.write(row)
if row_num >= 20:
break
text_file.close()
You could further improve this by using with blocks to open the files, rather than closing them explicitly. For example:
with open(file_path, "rb") as csvfile:
#your code here involving csvfile
#now the csvfile is closed!
Also note that Python might not be the best tool for this - you could do it directly from Bash, for example, with just head -n20 csvfile.csv > output.txt.

A simple solution would be to just do :
#!/usr/bin/python
# -*- encoding: utf-8 -*-
file_path = './test.csv'
with open(file_path, 'rb') as csvfile:
with open('output.txt', 'wb') as textfile:
for i, row in enumerate(csvfile):
textfile.write(row)
if i >= 20:
break
Explanation :
with open(file_path, 'rb') as csvfile:
with open('output.txt', 'wb') as textfile:
Instead of using open and close, it is recommended to use this line instead. Just write the lines that you want to execute when your file is opened into a new level of indentation.
'rb' and 'wb' are the keywords you need to open a file in respectively 'reading' and 'writing' in 'binary mode'
for i, row in enumerate(csvfile):
This line allows you to read line by line your CSV file, and using a tuple (i, row) gives you both the content of the row and its index. That's one of the awesome built-in functions from Python : check out here for more about it.
Hope this helps !
EDIT : Note that Python has a CSV package that can do that without enumerate :
# -*- encoding: utf-8 -*-
import csv
file_path = './test.csv'
with open(file_path, 'rb') as csvfile:
reader = csv.reader(csvfile)
with open('output.txt', 'wb') as textfile:
writer = csv.writer(textfile)
i = 0
while i<20:
row = next(reader)
writer.writerow(row)
i += 1
All we need to use is its reader and writer. They have functions next (that reads one line) and writerow (that writes one). Note that here, the variable row is not a string, but a list of strings, because the function does the split job by itself. It might be faster than the previous solution.
Also, this has the major advantage of allowing you to look anywhere you want in the file, no necessarily from the beginning (just change the bounds for i)

How to import data from a CSV file and store it in a variable?

I am extremely new to python 3 and I am learning as I go here. I figured someone could help me with a basic question: how to store text from a CSV file as a variable to be used later in the code. So the idea here would be to import a CSV file into the python interpreter:
import csv
with open('some.csv', 'rb') as f:
reader = csv.reader(f)
for row in reader:
...
and then extract the text from that file and store it as a variable (i.e. w = ["csv file text"]) to then be used later in the code to create permutations:
print (list(itertools.permutations(["w"], 2)))
If someone could please help and explain the process, it would be very much appreciated as I am really trying to learn. Please let me know if any more explanation is needed!

itertools.permutations() wants an iterable (e.g. a list) and a length as its arguments, so your data structure needs to reflect that, but you also need to define what you are trying to achieve here. For example, if you wanted to read a CSV file and produce permutations on every individual CSV field you could try this:
import csv
with open('some.csv', newline='') as f:
reader = csv.reader(f)
w = []
for row in reader:
w.extend(row)
print(list(itertools.permutations(w, 2)))
The key thing here is to create a flat list that can be passed to itertools.permutations() - this is done by intialising w to an empty list, and then extending its elements with the elements/fields from each row of the CSV file.
Note: As pointed out by #martineau, for the reasons explained here, the file should be opened with newline='' when used with the Python 3 csv module.

If you want to use Python 3 (as you state in the question) and to process the CSV file using the standard csv module, you should be careful about how to open the file. So far, your code and the answers use the Python 2 way of opening the CSV file. The things has changed in Python 3.
As shengy wrote, the CSV file is just a text file, and the csv module gets the elements as strings. Strings in Python 3 are unicode strings. Because of that, you should open the file in the text mode, and you should supply the encoding. Because of the nature of CSV file processing, you should also use the newline='' when opening the file.
Now extending the explanation of Burhan Khalid... When reading the CSV file, you get the rows as lists of strings. If you want to read all content of the CSV file into memory and store it in a variable, you probably want to use the list of rows (i.e. list of lists where the nested lists are the rows). The for loop iterates through the rows. The same way the list() function iterates through the sequence (here through the sequence of rows) and build the list of the items. To combine that with the wish to store everything in the content variable, you can write:
import csv
with open('some.csv', newline='', encoding='utf_8') as f:
reader = csv.reader(f)
content = list(reader)
Now you can do your permutation as you wish. The itertools is the correct way to do the permutations.

import csv
data = csv.DictReader(open('FileName.csv', 'r'))
print data.fieldnames
output = []
for each_row in data:
row = {}
try:
p = dict((k.strip(), v) for k, v in p.iteritems() if v.lower() != 'null')
except AttributeError, e:
print e
print p
raise Exception()
//based on the number of column
if p.get('col1'):
row['col1'] = p['col1']
if p.get('col2'):
row['col2'] = p['col2']
output.append(row)
Finally all data stored in output variable

Is this what you need?
import csv
with open('some.csv', 'rb') as f:
reader = csv.reader(f, delimiter=',')
rows = list(reader)
print('The csv file had {} rows'.format(len(rows)))
for row in rows:
do_stuff(row)
do_stuff_to_all_rows(rows)
The interesting line is rows = list(reader), which converts each row from the csv file (which will be a list), into another list rows, in effect giving you a list of lists.
If you had a csv file with three rows, rows would be a list with three elements, each element a row representing each line in the original csv file.

If all you care about is to read the raw text in the file (csv or not) then:
with open('some.csv') as f:
w = f.read()
will be a simple solution to having w="csv, file, text\nwithout, caring, about columns\n"

You should try pandas, which work both with Python 2.7 and Python 3.2+ :
import pandas as pd
csv = pd.read_csv("your_file.csv")
Then you can handle you data easily.
More fun here

First, a csv file is a text file too, so everything you can do with a file, you can do it with a csv file. That means f.read(), f.readline(), f.readlines() can all be used. see detailed information of these functions here.
But, as your file is a csv file, you can utilize the csv module.
# input.csv
# 1,david,enterprise
# 2,jeff,personal
import csv
with open('input.csv') as f:
reader = csv.reader(f)
for serial, name, version in reader:
# The csv module already extracts the information for you
print serial, name, version
More details about the csv module is here.

Python automating text data files into csv

I am trying to automate a process where in a specific folder, there are multiple text files following the same data format/structure. In the text files, the data is separated by a comma. I want to be able to output all of these text files into one cumulative csv file. This is what I currently have, and seem to be stuck where I am because of my lack of python knowledge.
from collections import defaultdict
import glob
def get_site_files():
sites = defaultdict(list)
for fname in glob.glob('*.txt'):
csv_out = csv.writer(open('out.csv', 'w'), delimiter=',')
f = open('myfile.txt')
for line in f:
vals = line.split(',')
csv_out.writerow()
f.close()
EDIT: bringing up comments: I want to make sure that all of the text files are read, not just only myfile.txt.
Also, if I could combine them all into one large .txt file and then I could make those into a csv that would be great too, I just am not sure the exact way to do this.

Just a little bit of reordering of your code.
import csv
import glob
def get_site_files():
with open('out.csv', 'w') as out_file:
csv_out = csv.writer(out_file, delimiter=',')
for fname in glob.glob('*.txt'):
with open(fname) as f:
for line in f:
vals = line.split(',')
csv_out.writerow(vals)
get_site_files()
But since they are all in the same format you can just concatenate them:
import glob
with ('out.csv', 'w') as fout:
for fname in glob.glob('*.txt'):
with open(fname, 'r') as fin:
fout.write(fin.read())

You could also try a different way:
I used os.listdir() once. That gives you a List of all the files in your directory. In combination with os.path.join you can manage all *.csv files in a certain directory.
Some additional Information can be found in the reference: os and os.path
So I would just loop through all the files in the directory (searching for them ending on ".csv"), for each of them, store each line in a list as a string, separate the strings by the colums delimiter, make "," to "." in the left strings and concatenate the strings again. Afterwards push each line of the list to the outputfile you wish to use
I highly recommend the python standard library for information about the total functionality of python to newbies ;)
Hope that helps ;)

I adapted the code above to covert text files to csv and get working code to convert all csv files in a folder to one text files appending all csv files. Works great.
import glob
import csv
def get_site_files():
with open('out.txt', 'w') as out_file:
csv_out = csv.writer(out_file, delimiter=',')
for fname in glob.glob('*.csv'):
with open(fname) as f:
for line in f:
vals = line.split(',')
csv_out.writerow(vals)enter code here