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for i, val in enumerate(seq):
Iteration Patterns

Meaning

The `for i, val in enumerate(seq):` construct iterates over any iterable while simultaneously providing the current index and the element value. It eliminates the need to manage a separate counter variable, reducing off‑by‑one errors and boilerplate code. Use it whenever you need to know an element’s position during a loop, such as when printing numbered lists or performing index‑based calculations.

Primary Function

Iteration

Communicative Purpose

Access both index and value in a loop without manually managing a counter.

Pattern

for index, value in enumerate(sequence):

Core Structure

for ... in enumerate(...):

Função primária

Iteration

Propósito comunicativo

Access both index and value in a loop without manually managing a counter.

Situações de gatilho

Data processing: printing a numbered list of items; Logging: prefixing log messages with line numbers; Algorithm design: accessing neighboring elements by index while iterating

Contextos

General Python code, data processing scripts, algorithm implementations, any scenario using sequences.

Padrão

for index, value in enumerate(sequence):

Estrutura central

for ... in enumerate(...):

Slots de substituição

index: int, value: element type, sequence: iterable

Colocados típicos

  • if condition
  • break
  • continue
  • list comprehension

Substituições comuns

  • range(len(seq)) to get index only
  • manual counter variable

Erros comuns

Using enumerate on a non‑iterable; forgetting to unpack both variables; assuming index starts at 1 (it starts at 0 unless you pass start).

Similar / contraste

while loop with manual index increment; zip for parallel iteration.

Interferências

Coming from C: manual index management → use enumerate to get index and value.

Família do chunk

  • for loop
  • range
  • zip
  • list comprehension

Nuance

enumerate returns an iterator; if you need a list of pairs, use list(enumerate(seq)). The start parameter can change the initial index.

Efeito pragmático

Makes code clearer and less error-prone by eliminating manual index management.

Dica de memória

Think 'enumerate gives you both index and value'.

Nota

Commonly used to avoid manual index management; the start parameter allows a custom starting index; returns an iterator, convert to list for multiple passes.

Upgrade path

Using enumerate with start parameter or converting to list for multiple passes.

Frequência: HighFormulaicidade: Semi-fixedTipo de construção: for-loop construct using the built-in enumerate functionPrioridade de aquisição: Active recallPrioridade de output: BothTag de espaçamento: Short-term

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