gh-121798: Add class method Decimal.from_number() #121801
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It is an alternate constructor which only accepts a single numeric argument. Unlike to Decimal.from_float() it accepts also Decimal. Unlike to the standard constructor, it does not accept strings and tuples.
Co-authored-by: Nice Zombies <[email protected]>
| >>> Decimal.from_number(Decimal('3.14')) # another decimal instance | ||
| Decimal('3.14') | ||
| """ | ||
| if isinstance(number, (int, Decimal, float)): |
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Yes, these are the only numeric types accepted by the constructor. Exact conversion from Fraction to Decimal is not possible in general case (e.g. 1/3).
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But it's possible from the Integral type.
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The main constructor does not accept the Integral type.
from_number() only supports a subset of values for the main constructor.
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Ah, then this does make sense.
Doc/library/decimal.rst
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| .. classmethod:: from_number(number) | ||
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| Alternative constructor that only accepts numbers (instances of |
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Instead of using number, maybe you can directly say "only accepts instances of float, int or Decimal" since otherwise people might wonder why objects implementing the Number protocol are not allowed.
By the way, this function is essentially a shortcut to avoid an if isinstance(...) right?
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Done.
Yes, you can look at it from such point. If your function needs a Decimal or a number that can be converted to Decimal, it can use Decimal.from_number() without additional type check. It will reject strings and tuples that are accepted by the constructor.
| >>> Decimal.from_number(Decimal('3.14')) # another decimal instance | ||
| Decimal('3.14') | ||
| """ | ||
| if isinstance(number, (int, Decimal, float)): |
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Ah, then this does make sense.
6 participants
It is an alternate constructor which only accepts a single numeric argument. Unlike to Decimal.from_float() it accepts also Decimal. Unlike to the standard constructor, it does not accept strings and tuples.
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