Indexing and substrings

Build the idea

Start with the concept and its key vocabulary.

Key idea

Translate ERL substring, left and right operations into correct Python indexing and slicing.

Strings are zero-indexed. OCR ERL substring(start, count) takes a starting index and a number of characters. Python string[start:end] takes an exclusive end index instead. ERL left(n) and right(n) map to Python [:n] and [-n:].

Index

The numeric position used to locate an item, starting at zero.

Zero-indexed

Numbered so the first character or item has index 0.

Substring

A consecutive section extracted from a larger string.

Slice

Python syntax that extracts values from a start index up to, but not including, an end index.

Keep these in mind

The first character has index 0.
ERL substring's second argument is a character count, not an end index.
Python excludes the slice end index.
The last index of a non-empty string is its length minus one.

Build the idea

Start with the concept and its key vocabulary.

Key idea

Translate ERL substring, left and right operations into correct Python indexing and slicing.

Index

The numeric position used to locate an item, starting at zero.

Zero-indexed

Numbered so the first character or item has index 0.

Substring

A consecutive section extracted from a larger string.

Slice

Python syntax that extracts values from a start index up to, but not including, an end index.

Keep these in mind

The first character has index 0.
ERL substring's second argument is a character count, not an end index.
Python excludes the slice end index.
The last index of a non-empty string is its length minus one.