Create a .csv file with values from a Python list

Question

I am trying to create a .csv file with the values from a Python list. When I print the values in the list they are all unicode (?), i.e. they look something like this

[u'value 1', u'value 2', ...]

If I iterate through the values in the list i.e. for v in mylist: print v they appear to be plain text.

And I can put a , between each with print ','.join(mylist)

And I can output to a file, i.e.

myfile = open(...)
print >>myfile, ','.join(mylist)

But I want to output to a CSV and have delimiters around the values in the list e.g.

"value 1", "value 2", ... 

I can't find an easy way to include the delimiters in the formatting, e.g. I have tried through the join statement. How can I do this?

Answer 1

import csv

with open(..., 'wb') as myfile:
    wr = csv.writer(myfile, quoting=csv.QUOTE_ALL)
    wr.writerow(mylist)

Edit: this only works with python 2.x.

To make it work with python 3.x replace wb with w (see this SO answer)

with open(..., 'w', newline='') as myfile:
     wr = csv.writer(myfile, quoting=csv.QUOTE_ALL)
     wr.writerow(mylist)

Answer 2

Here is a secure version of Alex Martelli's:

import csv

with open('filename', 'wb') as myfile:
    wr = csv.writer(myfile, quoting=csv.QUOTE_ALL)
    wr.writerow(mylist)

Answer 3

The best option I've found was using the savetxt from the numpy module:

import numpy as np
np.savetxt("file_name.csv", data1, delimiter=",", fmt='%s', header=header)

In case you have multiple lists that need to be stacked

np.savetxt("file_name.csv", np.column_stack((data1, data2)), delimiter=",", fmt='%s', header=header)

Answer 4

For another approach, you can use DataFrame in pandas: And it can easily dump the data to csv just like the code below:

import pandas
df = pandas.DataFrame(data={"col1": list_1, "col2": list_2})
df.to_csv("./file.csv", sep=',',index=False)

Answer 5

Use python's csv module for reading and writing comma or tab-delimited files. The csv module is preferred because it gives you good control over quoting.

For example, here is the worked example for you:

import csv
data = ["value %d" % i for i in range(1,4)]

out = csv.writer(open("myfile.csv","w"), delimiter=',',quoting=csv.QUOTE_ALL)
out.writerow(data)

Produces:

"value 1","value 2","value 3"

Answer 6

You could use the string.join method in this case.

Split over a few of lines for clarity - here's an interactive session

>>> a = ['a','b','c']
>>> first = '", "'.join(a)
>>> second = '"%s"' % first
>>> print second
"a", "b", "c"

Or as a single line

>>> print ('"%s"') % '", "'.join(a)
"a", "b", "c"

However, you may have a problem is your strings have got embedded quotes. If this is the case you'll need to decide how to escape them.

The CSV module can take care of all of this for you, allowing you to choose between various quoting options (all fields, only fields with quotes and seperators, only non numeric fields, etc) and how to esacpe control charecters (double quotes, or escaped strings). If your values are simple, string.join will probably be OK but if you're having to manage lots of edge cases, use the module available.

Answer 7

Jupyter notebook

Lets say that your list is A

Then you can code the following ad you will have it as a csv file (columns only!)

R="\n".join(A)
f = open('Columns.csv','w')
f.write(R)
f.close()

Answer 8

you should use the CSV module for sure , but the chances are , you need to write unicode . For those Who need to write unicode , this is the class from example page , that you can use as a util module:

import csv, codecs, cStringIO

class UTF8Recoder:
    """
    Iterator that reads an encoded stream and reencodes the input to UTF-8
    """
    def __init__(self, f, encoding):
        self.reader = codecs.getreader(encoding)(f)

def __iter__(self):
    return self

def next(self):
    return self.reader.next().encode("utf-8")

class UnicodeReader:
    """
    A CSV reader which will iterate over lines in the CSV file "f",
    which is encoded in the given encoding.
    """

def __init__(self, f, dialect=csv.excel, encoding="utf-8", **kwds):
    f = UTF8Recoder(f, encoding)
    self.reader = csv.reader(f, dialect=dialect, **kwds)

def next(self):
    row = self.reader.next()
    return [unicode(s, "utf-8") for s in row]

def __iter__(self):
    return self

class UnicodeWriter:
    """
    A CSV writer which will write rows to CSV file "f",
    which is encoded in the given encoding.
"""

def __init__(self, f, dialect=csv.excel, encoding="utf-8", **kwds):
    # Redirect output to a queue
    self.queue = cStringIO.StringIO()
    self.writer = csv.writer(self.queue, dialect=dialect, **kwds)
    self.stream = f
    self.encoder = codecs.getincrementalencoder(encoding)()

def writerow(self, row):
    self.writer.writerow([s.encode("utf-8") for s in row])
    # Fetch UTF-8 output from the queue ...
    data = self.queue.getvalue()
    data = data.decode("utf-8")
    # ... and reencode it into the target encoding
    data = self.encoder.encode(data)
    # write to the target stream
    self.stream.write(data)
    # empty queue
    self.queue.truncate(0)

def writerows(self, rows):
    for row in rows:
        self.writerow(row)

Answer 9

Here is another solution that does not require the csv module.

print ', '.join(['"'+i+'"' for i in myList])

Example :

>>> myList = [u'value 1', u'value 2', u'value 3']
>>> print ', '.join(['"'+i+'"' for i in myList])
"value 1", "value 2", "value 3"

However, if the initial list contains some ", they will not be escaped. If it is required, it is possible to call a function to escape it like that :

print ', '.join(['"'+myFunction(i)+'"' for i in myList])

Answer 10

This solutions sounds crazy, but works smooth as honey

import csv

with open('filename', 'wb') as myfile:
    wr = csv.writer(myfile, quoting=csv.QUOTE_ALL,delimiter='\n')
    wr.writerow(mylist)

The file is being written by csvwriter hence csv properties are maintained i.e. comma separated. The delimiter helps in the main part by moving list items to next line, each time.