CODEWITHSUNDEEP
pythonstringf-string
Alex Man
Alex Man

Reputation: 477

Convert various number of arguments into a string?

I have the following function that create a name from the variable size arguments:

def create_name(*argv):
    """Create a name from passed arguments."""
    return f"%s" % "_".join(str(arg) for arg in argv)

When running pylint, i am getting the following warning.

 W1309: Using an f-string that does not have any interpolated variables (f-string-without-interpolation)

Just curious if any improvement can be made to resolve this warning.

Upvotes: 1

Views: 795

Answers (1)

Grismar
Grismar

Reputation: 31319

Your expression f"%s" % "_".join(str(arg) for arg in argv) breaks down like this:

  • f"%s" is formatted with "_".join(str(arg) for arg in argv), using the % operator
  • f"%s" in turn is an interpolated string, but nothing is done to it since there's no {} in it, so "%s" would achieve the same
  • formatting "%s" with another string using % just gets you the same string again, so the whole expression could just be "_".join(str(arg) for arg in argv)

So, these all work:

return "_".join(str(arg) for arg in argv)
return "%s" % "_".join(str(arg) for arg in argv)
return f'{"_".join(str(arg) for arg in argv)}'

But there's little reason not to use the first, the rest just adds complications and no functionality.

Specifically, you're issued that warning because interpolated strings (or 'f-strings') in Python expect expressions in {} to replace, but your f-string doesn't have any, so pylint is telling you you can just remove the f. Because your f-string "does not have any interpolated variables".

Upvotes: 3

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