# Source code for qcodes.plotting.axis_labels

```"""
This file holds scaling logic for axis that is independent of plotting backend
"""
from collections import OrderedDict
from typing import Dict, Set, Tuple

import numpy as np

_UNITS_FOR_RESCALING: Set[str] = {
# SI units (without some irrelevant ones like candela)
# 'kg' is not included because it is 'kilo' and rarely used
"m",
"s",
"A",
"K",
"mol",
"Hz",
"N",
"Pa",
"J",
"W",
"C",
"V",
"F",
"ohm",
"Ohm",
"Ω",
"\N{GREEK CAPITAL LETTER OMEGA}",
"S",
"Wb",
"T",
"H",
# non-SI units as well, for convenience
"eV",
"g",
}

_ENGINEERING_PREFIXES: Dict[int, str] = OrderedDict(
{
-24: "y",
-21: "z",
-18: "a",
-15: "f",
-12: "p",
-9: "n",
-6: "\N{GREEK SMALL LETTER MU}",
-3: "m",
0: "",
3: "k",
6: "M",
9: "G",
12: "T",
15: "P",
18: "E",
21: "Z",
24: "Y",
}
)

_THRESHOLDS: Dict[float, int] = OrderedDict(
{10 ** (scale + 3): scale for scale in _ENGINEERING_PREFIXES.keys()}
)

[docs]def find_scale_and_prefix(data: np.ndarray, unit: str) -> Tuple[str, int]:
"""
Given a numpy array of data and a unit find the best engineering prefix
and matching scale that best describes the data.

The units for which unit prefixes are added can be found in
``_UNITS_FOR_RESCALING``. For all other units
the prefix is an exponential scaling factor e.g. ``10^3``.
If no unit is given (i.e. an empty string) no scaling is performed.

Args:
data: A numpy array of data.
unit: The unit the data is measured in.
Should not contain a prefix already.

Returns:
tuple of prefix and exponential scale

"""
maxval = np.nanmax(np.abs(data))
if unit in _UNITS_FOR_RESCALING:
for threshold, scale in _THRESHOLDS.items():
if maxval == 0.0:
# handle all zero data
selected_scale = 0
prefix = _ENGINEERING_PREFIXES[selected_scale]
break
if maxval < threshold:
selected_scale = scale
prefix = _ENGINEERING_PREFIXES[scale]
break
else:
# here, maxval is larger than the largest threshold
largest_scale = max(list(_ENGINEERING_PREFIXES.keys()))
selected_scale = largest_scale
prefix = _ENGINEERING_PREFIXES[largest_scale]
elif unit != "":
if maxval > 0:
selected_scale = 3 * (np.floor(np.floor(np.log10(maxval)) / 3))
else:
selected_scale = 0
if selected_scale != 0:
prefix = f"\$10^{{{selected_scale:.0f}}}\$ "
else:
prefix = ""
else:
prefix = ""
selected_scale = 0
return prefix, selected_scale
```