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What is the memory difference between a list comprehension and a generator expression?

Q: What is the memory difference between a list comprehension and a generator expression?

A **list comprehension** `[...]` builds the entire list in memory; a **generator expression** `(...)` produces items lazily one at a time. For large data or single-pass aggregation (e.g. `sum(x*x for x in data)`), generators save memory.

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Compare comprehensions.

generator-expression

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A list comprehension [...] builds the entire list in memory; a generator expression (...) produces items lazily one at a time. For large data or single-pass aggregation (e.g. sum(x*x for x in data)), generators save memory.

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PYsys.getsizeof: list grows, generator stays tiny

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