Python inserting variable string as file name

Question

I'm trying to create a file with a unique file name for every time my script runs. I am only intending to do this to every week or month. so I chose to use the date for the file name.

f = open('%s.csv', 'wb') %name

is where I'm getting this error.

Traceback (most recent call last):
File "C:\Users\User\workspace\new3\stjohnsinvoices\BabblevoiceInvoiceswpath.py", line 143,      in <module>
f = open('%s.csv', 'ab') %name
TypeError: unsupported operand type(s) for %: 'file' and 'str'

it works if I use a static filename, is there an issue with the open function, that means you can't pass a string like this?

name is a string and has values such as :

31/1/2013BVI

Many thanks for any help.

Volatility · Accepted Answer · 2013-01-31 09:27:34Z

51

You need to put % name straight after the string:

f = open('%s.csv' % name, 'wb')

The reason your code doesn't work is because you are trying to % a file, which isn't string formatting, and is also invalid.

answered Jan 31, 2013 at 9:27

Volatility

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Comments

ran632 · Accepted Answer · 2021-02-04 15:43:03Z

8

Very similar to peixe.
You don't have to mention the number if the variables you add as parameters are in order of appearance

f = open('{}.csv'.format(name), 'wb')

Another option - the f-string formatting (ref):

f = open(f"{name}.csv", 'wb')

edited Feb 4, 2021 at 15:43

answered Feb 15, 2018 at 8:21

ran632

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avasal · Accepted Answer · 2013-01-31 09:27:27Z

7

you can do something like

filename = "%s.csv" % name
f = open(filename , 'wb')

or f = open('%s.csv' % name, 'wb')

answered Jan 31, 2013 at 9:27

avasal

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peixe · Accepted Answer · 2013-01-31 09:33:25Z

5

And with the new string formatting method...

f = open('{0}.csv'.format(name), 'wb')

answered Jan 31, 2013 at 9:33

peixe

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Tom Lubenow · Accepted Answer · 2019-05-09 16:15:39Z

5

Even better are f-strings in python 3!

f = open(f'{name}.csv', 'wb')

answered May 9, 2019 at 16:15

Tom Lubenow

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elby · Accepted Answer · 2022-02-25 09:42:38Z

-1

import hashlib

filename = file_for_download
with open(filename, "rb") as f:
    bytes = f.read()  # read entire file as bytes
    msg_hash = hashlib.sha256(bytes).hexdigest();
    print(f"MSG_HASH = {msg_hash}")

answered Feb 25, 2022 at 9:42

elby

1

2 Comments

Muhammad Mohsin Khan Over a year ago

A code-only answer is not high quality. While this code may be useful, you can improve it by saying why it works, how it works, when it should be used, and what its limitations are. Please edit your answer to include explanation and link to relevant documentation.

wovano Over a year ago

This also does not answer the question.

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