qiskit.utils.detach_prefix

detach_prefix(value, decimal=None)

Given a SI unit value, find the most suitable prefix to scale the value.

For example, the value = 1.3e8 will be converted into a tuple of (130.0, "M"), which represents a scaled value and auxiliary unit that may be used to display the value. In above example, that value might be displayed as 130 MHz (unit is arbitrary here).

Example

>>> value, prefix = detach_prefix(1e4)
>>> print(f"{value} {prefix}Hz")
10 kHz

Parameters

• value (float) – The number to find prefix.

• decimal (Optional[int]) – Optional. An arbitrary integer number to represent a precision of the value. If specified, it tries to round the mantissa and adjust the prefix to rounded value. For example, 999_999.91 will become 999.9999 k with decimal=4, while 1.0 M with decimal=3 or less.

Return type

Tuple[float, str]

Returns

A tuple of scaled value and prefix.

Note

This may induce tiny value error due to internal representation of float object. See https://docs.python.org/3/tutorial/floatingpoint.html for details.

Raises

• ValueError – If the value is out of range.

• ValueError – If the value is not real number.