Format string with substrings

Question

I need to format a string with substrings of a variable. If I do:

sample="1234567890XXXX"
f"{sample[:5]}/{sample[5:10]}/{sample}/config"

It works fine:

'12345/67890/1234567890XXXX/config'

But if I use format:

"{sample[:5]}/{sample[5:10]}/{sample}/config".format(sample="1234567890XXXX")

I get an error:

TypeError: string indices must be integers, not 'str'

Any way to make it work with a format?

EDIT: just to clarify some things. The format string is passed through a command line argument and the format arguments automatically extracted from a pandas dataframe (as a dict). So, I do not thing the propsed solutions (f-strings and extra format arguments) will work.

args.out_path.format(**name)

Slice the strings and pass the slices as multiple arguments to format: "{s1}/{s2}/{sample}/config".format(sample="1234567890XXXX", s1={sample[:5]}, s2={sample[5:10]}) — pho
– pho, Commented Nov 20, 2023 at 14:26
What's wrong with using f-string, which is way more readble? — buran
– buran, Commented Nov 20, 2023 at 14:35
Because i want the format string to be passed as a command line argument, so I don't think the f-string will work. And neither will multiple arguments to format. — FGV
– FGV, Commented Nov 22, 2023 at 10:12

Talha Tayyab · Accepted Answer · 2023-11-20 14:50:37Z

As @pho suggested you can supply the slices to str.format():

"{s1}/{s2}/{sample}/config".format(sample="1234567890XXXX", s1=sample[:5], s2=sample[5:10])

#output
'12345/67890/1234567890XXXX/config'

Python f-strings are very different from str.format() templates. Python f-strings support slicing and don't use a "mini-language" like the formatter. The full power of a python expression is available within each curly-brace of an f-string.

“Format specifications” are used within replacement fields contained within a format string to define how individual values are presented (see Format String Syntax and Formatted string literals). They can also be passed directly to the built-in format() function. Each formattable type may define how the format specification is to be interpreted.

https://docs.python.org/3/library/string.html#format-specification-mini-language

No, slicing is not supported by builtin str formatting. Although, there is a workaround in case f-strings (runtime evaluated) don't fit your needs.

You can use a run-time evaluated "f" string. Python f-strings support slicing and don't use a "mini-language" like the formatter.

https://stackoverflow.com/a/62024873/13086128

https://stackoverflow.com/a/49884004/13086128

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