Created SITools Module

This module
 - converts numbers to strings wih SI prefixed unit represention.
 - parses  strings with SI values

NanoVNASaver/SITools.py

@@ -0,0 +1,91 @@
+import math
+from numbers import Number
+
+PREFIXES = ("y", "z", "a", "f", "p", "n", "µ", "m",
+            "", "k", "M", "G", "T", "P", "E", "Z", "Y")
+
+
+class Format(object):
+    def __init__(self,
+                 max_nr_digits: int = 6,
+                 fix_decimals: bool = False,
+                 space_str: str = "",
+                 assume_infinity: bool = True,
+                 min_offset: int = -8,
+                 max_offset: int = 8):
+        assert(min_offset >= -8 and max_offset <= 8 and
+               min_offset < max_offset)
+        self.max_nr_digits = max_nr_digits
+        self.fix_decimals = fix_decimals
+        self.space_str = space_str
+        self.assume_infinity = assume_infinity
+        self.min_offset = min_offset
+        self.max_offset = max_offset
+
+    def __repr__(self):
+        return (f"{self.__class__.__name__}("
+                f"{self.max_nr_digits}, {self.fix_decimals}, "
+                f"'{self.space_str}', {self.assume_infinity}, "
+                f"{self.min_offset}, {self.max_offset})")
+
+
+class Value(object):
+    def __init__(self, value: Number = 0, unit: str = "", fmt=Format()):
+        self.value = value
+        self._unit = unit
+        self.fmt = fmt
+
+    def __repr__(self):
+        return (f"{self.__class__.__name__}("
+                f"{self.value}, '{self._unit}', {self.fmt})")
+
+    def __str__(self):
+        fmt = self.fmt
+        if fmt.assume_infinity and \
+                abs(self.value) >= 10 ** ((fmt.max_offset + 1) * 3):
+            return (("-" if self.value < 0 else "") +
+                    "\N{INFINITY}" + fmt.space_str + self._unit)
+
+        if self.value == 0:
+            offset = 0
+        else:
+            offset = int(math.log10(abs(self.value)) // 3)
+
+        if offset < fmt.min_offset:
+            offset = fmt.min_offset
+        elif offset > fmt.max_offset:
+            offset = fmt.max_offset
+
+        real = self.value / (10 ** (offset * 3))
+
+        if fmt.max_nr_digits < 4:
+            formstr = ".0f"
+        else:
+            fmt.max_nr_digits += (
+                (1 if not fmt.fix_decimals and real < 10 else 0) +
+                (1 if not fmt.fix_decimals and real < 100 else 0))
+            formstr = "." + str(fmt.max_nr_digits - 3) + "f"
+
+        result = format(real, formstr)
+
+        if float(result) == 0.0:
+            offset = 0
+
+        return result + fmt.space_str + PREFIXES[offset + 8] + self._unit
+
+
+    def parse(self, value: str):
+        value = value.replace(" ", "")  # Ignore spaces
+        if self._unit and value.endswith(self._unit):  # strip unit
+            value = value[:-len(self._unit)]
+
+        factor = 1
+        if value[-1] in PREFIXES:
+            factor = 10 ** ((PREFIXES.index(value[-1]) - 8) * 3)
+            value = value[:-1]
+        self.value = float(value) * factor
+        return self.value
+
+    @property
+    def unit(self):
+        return self._unit