Python range and enumerate: indexes are not stable record identities

Operation contract

The batch labels use a one-based presentation index alongside an unchanged receipt identifier. Range supplies selected positions without allocating a list of every number. An empty range is valid. Its stop is exclusive, and a zero step is invalid. These rules support bounded loop work when the selected input itself is bounded.

Failure and ownership boundary

An index can shift after insertion, deletion or filtering. Do not use it as a durable receipt ID. Enumerate consumes its iterable lazily and does not freeze referenced records. A range’s compact representation does not make iterating a billion positions cheap. Python list slicing: half-open ranges and shallow ownership and Python variables: names refer to objects, assignment does not copy distinguish representation from work and ownership.

Working program

receipt_ids = ["R-0041", "R-0042"]
print(list(enumerate(receipt_ids, start=1)))
print(list(range(2, 9, 3)))
print(list(range(4, 4)))
try:
    range(1, 4, 0)
except ValueError:
    print("zero step rejected")

Output

[(1, 'R-0041'), (2, 'R-0042')]
[2, 5, 8]
[]
zero step rejected

Costs and limits

A range stores a bounded number of integer parameters, excluding their digit storage. Enumerate retains iterator/counter state rather than duplicating n entries. Materializing either result takes O(n) retained entries and iteration work.

Common Mistakes

• The stop endpoint is excluded.
• A display position is not a stable identity for a stored record.

Connected lessons

Python list slicing: half-open ranges and shallow ownership, Python variables: names refer to objects, assignment does not copy, Python iterators: exhaustion and repeatable collection ownership.