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Slicing can be enhanced with a step argument, which allows you to extract characters at specific intervals.

This is useful when you want to select every second character, skip letters, or extract patterns from structured data like invoice numbers, transaction codes, or reports.

string[start : end : step]

start: the index where slicing begins (inclusive)
end: the index where slicing ends (exclusive)
step: the interval (e.g., 2 means every second character)

You can also omit one or more values:

string[::2] takes every second character from start to end;
string[5::3] starts at index 5 and takes every third character;
string[:-2:2] takes every second character from the beginning up to (but not including) the second-to-last character.

Example


              123
            
code = "TXN-2024-INV-0007"
sliced = code[0:13:5]
print(sliced)  # Output: T0N

We start at index 0
End at index 13 (exclusive)
Use a step of 5, which means: take every fifth character

Characters at indexes 0, 5, and 10 are 'T', '0', and 'N', so the output is 'T0N'.

This kind of slicing could be used to extract initials or control codes from structured strings in financial or document systems.

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In an accounting system, filenames for financial reports are generated automatically. Each filename includes a prefix, the report type, and the year.

Your task is to use slicing with a step to extract the 1st and 3rd digits of the year (in this case, 2 and 2) from the filename. This result will serve as a simple year control code.

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Sektion 3. Kapitel 7

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Suggested prompts:

Can you explain how negative steps work in slicing?

What happens if the step value is larger than the string length?

Can you show more examples of using slicing with different step values?

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