Using items in list to create file name - for loop

Question

I have a list that I am using for a for-loop.
Each item in the list has an action carried out, but I want to write a file for what has happened.
How can I use the variable in the for loop to create specific file names for each item in the list?

mylist = ['hello', 'there', 'world']
for i in mylist:
    outputfile = open('%i.csv', 'a')
    print('hello there moon', file=outputfile)

Am I on the right track using %i to represent individual items in the list?

Does this answer your question? Creating a new file, filename contains loop variable, python — Trenton McKinney
– Trenton McKinney, Commented Jun 20, 2020 at 20:28

Martin Evans · Accepted Answer · 2017-05-24 11:39:20Z

8

You can use format() to do what you need as follows:

mylist = ['hello', 'there', 'world']

for word in mylist:
    with open('{}.csv'.format(word), 'a') as f_output:
        print('hello there moon', file=f_output)

Using with will also automatically close your file afterwards.

format() has many possible features to allow all kinds of string formatting, but the simple case is to replace a {} with an argument, in your case a word.

edited May 24, 2017 at 11:39

answered May 24, 2017 at 11:24

Martin Evans

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Comments

Ahmed Ashour · Accepted Answer · 2017-05-24 11:29:15Z

3

Use following code.

mylist = ['hello', 'there', 'world']
for i in mylist:
    outputfile = open('%s.csv'%i, 'a')
    print('hello there moon', file=outputfile)
    outputfile.close()

edited May 24, 2017 at 11:29

Ahmed Ashour

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answered May 24, 2017 at 11:24

Jay Parikh

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Comments

zanseb · Accepted Answer · 2017-05-24 11:25:06Z

2

You should use %s since the items in the list are strings.

outputfile = open('%s.csv' % i, 'a')

answered May 24, 2017 at 11:25

zanseb

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Comments

deepayan das · Accepted Answer · 2017-05-24 11:40:00Z

1

mylist = ['hello', 'there', 'world']
for item in mylist:
   with open('%s.txt'%item,'a') as in_file:
      in_file.write('hello there moon')

answered May 24, 2017 at 11:40

deepayan das

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Trenton McKinney · Accepted Answer · 2021-05-21 15:22:57Z

Use f-strings

This is the simplest and most recent implementation of string formatting.
f-Strings: A New and Improved Way to Format Strings in Python
PEP 498 - Literal String Interpolation
The string is preceded by an f and the variable is inside the string quotes, surrounded by {}.
- f'{i}.csv'
Reading and Writing Files
- The advantage is that the file is properly closed after its suite finishes, even if an exception is raised at some point.

Using code from OP

mylist = ['hello', 'there', 'world']
for i in mylist:

    # open the file
    outputfile = open(f'{i}.csv', 'a')

    # write to the file
    print('hello there moon', file=outputfile)

    # close the file
    outputfile.close()

Close the file using `with`

mylist = ['hello', 'there', 'world']
for i in mylist:

    with open(f'{i}.csv', 'a') as outputfile:

        outputfile.write('hello there moon')

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Close the file using `with`