Python list to csv string

Create a .csv file with values from a Python list

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) 

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?

Thanks everyone, I have combined the ideas from a few answers to solve my question 🙂 I now use the csv module to write the [. ] data straight into a file import csv data = [. ] myfile = open(. ‘wb’) out = csv.writer(open(«myfile.csv»,»w»), delimiter=’,’,quoting=csv.QUOTE_ALL) out.writerow(data) works well, I construct my data[] by grabbing some data out a spreadsheet using xlrd and the csv module writes it out to a file with the right delimiters all good 🙂 ty all again

13 Answers 13

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) 

Do note that the csv module in 2.x does not deal properly with unicodes; see the module documentation for examples on how to deal with this. docs.python.org/library/csv.html

Writerows seems to break up each element in the list into columns if each element is a list as well. This is pretty handy for outputting tables.

That does not work with python 3.4. I am getting TypeError: ‘str’ does not support the buffer interface .

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) 

If I am using this inside a for loop, should the entire with block be nested under the for loop? Or would it be more efficient to only have wr.writerow(my_list) inside the loop?

@crypdick you should definitely not put the entire block into the loop. Open the file, then write each row in a loop. There’s no need to open the file n times to write n rows.

If you are writing string objects to a file, would suggest using ‘wt’ while opening file to avoid TypeError: a bytes-like object is required, not ‘str’.

To avoid using with , instead use f = open(«myfile.csv»,»w») , out = csv.writer(f, delimiter=’,’,quoting=csv.QUOTE_ALL) , out.writerow([11,22,338]) , f.close()

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=) df.to_csv("./file.csv", sep=',',index=False) 

Thank you for this code snippet, which may provide some immediate help. A proper explanation would greatly improve its educational value by showing why this is a good solution to the problem, and would make it more useful to future readers with similar, but not identical, questions. Please edit your answer to add explanation, and give an indication of what limitations and assumptions apply.

Also for this to work the lists need to have the same length, otherwise you’ll get a ValueError (pandas v 0.22.0)

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) 

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) 

First run is empty and you also cannot delete it then, because it is then opened in python. Second run (or more precise: out = csv.writer(open(«myfile.csv»,»w»), delimiter=’,’,quoting=csv.QUOTE_ALL)) fills the data, no matter if you put open(«myfile.csv»,»w») or a new file open(«myfile2.csv»,»w») . Seems as if the out object cannot deal with the file object built on the run, but stores the output process as a todo. In otherwords: the out object stores the file object in the first run but is only writing when the file object already exists! See the right solution below @Saurabh Adhikary

Jupyter notebook

Let’s say that your list name is A

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

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

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" 

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.

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.

works, and if you have a nested list, expanding the example of @vy32, you have: data = [[«value %d» % i, «value %d» % (i+1)] for i in range(1,4)] with open(«myfile.txt»,»w») as f: out = csv.writer(f, quoting=csv.QUOTE_ALL, delimiter=’\n’) out.writerow([‘;’.join(x) for x in data])

Here is working copy-paste example for Python 3.x with options to define your own delimiter and quote char.

import csv mylist = ['value 1', 'value 2', 'value 3'] with open('employee_file.csv', mode='w') as employee_file: employee_writer = csv.writer(employee_file, delimiter=',', quotechar='"', quoting=csv.QUOTE_ALL) employee_writer.writerow(mylist) 

This will generate employee_file.csv that looks like this:

NOTE:

If quoting is set to csv.QUOTE_MINIMAL , then .writerow() will quote fields only if they contain the delimiter or the quotechar. This is the default case.

If quoting is set to csv.QUOTE_ALL , then .writerow() will quote all fields.

If quoting is set to csv.QUOTE_NONNUMERIC , then .writerow() will quote all fields containing text data and convert all numeric fields to the float data type.

If quoting is set to csv.QUOTE_NONE , then .writerow() will escape delimiters instead of quoting them. In this case, you also must provide a value for the escapechar optional parameter.

To create and write into a csv file

The below example demonstrate creating and writing a csv file. to make a dynamic file writer we need to import a package import csv, then need to create an instance of the file with file reference Ex:- with open(«D:\sample.csv»,»w»,newline=»») as file_writer

here if the file does not exist with the mentioned file directory then python will create a same file in the specified directory, and «w» represents write, if you want to read a file then replace «w» with «r» or to append to existing file then «a». newline=»» specifies that it removes an extra empty row for every time you create row so to eliminate empty row we use newline=»», create some field names(column names) using list like fields=[«Names»,»Age»,»Class»], then apply to writer instance like writer=csv.DictWriter(file_writer,fieldnames=fields) here using Dictionary writer and assigning column names, to write column names to csv we use writer.writeheader() and to write values we use writer.writerow() ,while writing file values must be passed using dictionary method , here the key is column name and value is your respective key value

import csv with open("D:\\sample.csv","w",newline="") as file_writer: fields=["Names","Age","Class"] writer=csv.DictWriter(file_writer,fieldnames=fields) writer.writeheader() writer.writerow() 

For those looking for less complicated solution. I actually find this one more simplisitic solution that will do similar job:

import pandas as pd a = ['a','b','c'] df = pd.DataFrame() df= df.set_index('a').T df.to_csv('list_a.csv', index=False) 

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) 

Источник

Python – Convert List to CSV String

To convert a given list of values to a CSV (Comma Separated Value) string in Python, call join() method on the separator string, and pass the list as argument.

The string join() method join the given list of values into a string with the separator string in between the elements.

The syntax of the expression that returns a CSV string from a given list of values x is

Note: If the elements in list are of not string type, join() method can raise TypeError. Before passing the given list as argument to join() method, convert the elements to string type.

Examples

1. Convert list of string values to CSV string

In the following example, we take a list of strings in x, and convert this list into a CSV string.

Python Program

x = ['apple', 'banana', 'cherry'] output = ','.join(x) print(output)

2. Convert list of integer values to CSV string

In the following example, we take a list of integers in x, and convert this list into a CSV string.

Since, the elements are not of string type, we convert them to string before passing the list as argument to join() method.

Python Program

x = [21, 14, 44, 8, 62] #convert integer values to string values x = [str(value) for value in x] #convert list to CSV string output = ','.join(x) print(output)

Summary

In this tutorial of Python Examples, we learned how to convert a list of values to a CSV string using join() method, with the help of examples.

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