Unit converter

== Unit converter ==
1) length  2) weight  3) temperature  4) volume  5) reverse last  6) quit
choice> 5
Nothing to reverse yet.

== Unit converter ==
1) length  2) weight  3) temperature  4) volume  5) reverse last  6) quit
choice> 9
Pick a number from 1 to 6.

== Unit converter ==
1) length  2) weight  3) temperature  4) volume  5) reverse last  6) quit
choice> 
Pick a number from 1 to 6.

== Unit converter ==
1) length  2) weight  3) temperature  4) volume  5) reverse last  6) quit
choice>  1
length units: mm cm m km in ft yd mi
from> parsec
Unknown unit: parsec. length units: mm cm m km in ft yd mi

== Unit converter ==
1) length  2) weight  3) temperature  4) volume  5) reverse last  6) quit
choice> 1
length units: mm cm m km in ft yd mi
from> 
Type a unit.

== Unit converter ==
1) length  2) weight  3) temperature  4) volume  5) reverse last  6) quit
choice> 1
length units: mm cm m km in ft yd mi
from> kg
kg is a weight unit, not a length unit.

== Unit converter ==
1) length  2) weight  3) temperature  4) volume  5) reverse last  6) quit
choice> 1
length units: mm cm m km in ft yd mi
from>   km
to> mi
value in km> abc
Not a number: abc

== Unit converter ==
1) length  2) weight  3) temperature  4) volume  5) reverse last  6) quit
choice> 1
length units: mm cm m km in ft yd mi
from> km
to> m
value in km> 
Type a number.

== Unit converter ==
1) length  2) weight  3) temperature  4) volume  5) reverse last  6) quit
choice> 1
length units: mm cm m km in ft yd mi
from> km
to> m
value in km> -3
A length cannot be negative.

== Unit converter ==
1) length  2) weight  3) temperature  4) volume  5) reverse last  6) quit
choice> 3
temperature units: C F K
from> F
to> C
value in F> -500
-500 F is below absolute zero (-459.67 F).

== Unit converter ==
1) length  2) weight  3) temperature  4) volume  5) reverse last  6) quit
choice> 3
temperature units: C F K
from> K
to> C
value in K> -0.5
-0.5 K is below absolute zero (0 K).

== Unit converter ==
1) length  2) weight  3) temperature  4) volume  5) reverse last  6) quit
choice> 2
weight units: mg g kg t oz lb
from> g
to> oz
value in g> nan
Not a finite number: nan

== Unit converter ==
1) length  2) weight  3) temperature  4) volume  5) reverse last  6) quit
choice> 2
weight units: mg g kg t oz lb
from> g
to> oz
value in g> inf
Not a finite number: inf

== Unit converter ==
1) length  2) weight  3) temperature  4) volume  5) reverse last  6) quit
choice> 4
volume units: ml l m3 tsp tbsp floz cup pt qt gal
from> l
to> l
value in l> -0
0 l = 0 l

== Unit converter ==
1) length  2) weight  3) temperature  4) volume  5) reverse last  6) quit
choice> 5
0 l = 0 l

== Unit converter ==
1) length  2) weight  3) temperature  4) volume  5) reverse last  6) quit
choice> 6
Bye.

5
9

 1
parsec
1

1
kg
1
  km
mi
abc
1
km
m

1
km
m
-3
3
F
C
-500
3
K
C
-0.5
2
g
oz
nan
2
g
oz
inf
4
l
l
-0
5
6

== Unit converter ==
1) length  2) weight  3) temperature  4) volume  5) reverse last  6) quit
choice> 1
length units: mm cm m km in ft yd mi
from> km
to> mi
value in km> 10
10 km = 6.21371 mi

== Unit converter ==
1) length  2) weight  3) temperature  4) volume  5) reverse last  6) quit
choice> 5
6.21371 mi = 10 km

== Unit converter ==
1) length  2) weight  3) temperature  4) volume  5) reverse last  6) quit
choice> 2
weight units: mg g kg t oz lb
from> lb
to> kg
value in lb> 150
150 lb = 68.0389 kg

== Unit converter ==
1) length  2) weight  3) temperature  4) volume  5) reverse last  6) quit
choice> 3
temperature units: C F K
from> F
to> C
value in F> 98.6
98.6 F = 37 C

== Unit converter ==
1) length  2) weight  3) temperature  4) volume  5) reverse last  6) quit
choice> 3
temperature units: C F K
from> C
to> F
value in C> 100
100 C = 212 F

== Unit converter ==
1) length  2) weight  3) temperature  4) volume  5) reverse last  6) quit
choice> 3
temperature units: C F K
from> K
to> C
value in K> 0
0 K = -273.15 C

== Unit converter ==
1) length  2) weight  3) temperature  4) volume  5) reverse last  6) quit
choice> 4
volume units: ml l m3 tsp tbsp floz cup pt qt gal
from> gal
to> l
value in gal> 2
2 gal = 7.57082 l

== Unit converter ==
1) length  2) weight  3) temperature  4) volume  5) reverse last  6) quit
choice> 4
volume units: ml l m3 tsp tbsp floz cup pt qt gal
from> cup
to> ml
value in cup> 1
1 cup = 236.588 ml

== Unit converter ==
1) length  2) weight  3) temperature  4) volume  5) reverse last  6) quit
choice> 5
236.588 ml = 1 cup

== Unit converter ==
1) length  2) weight  3) temperature  4) volume  5) reverse last  6) quit
choice> 1
length units: mm cm m km in ft yd mi
from> ft
to> cm
value in ft> 6
6 ft = 182.88 cm

== Unit converter ==
1) length  2) weight  3) temperature  4) volume  5) reverse last  6) quit
choice> 6
Bye.

1
km
mi
10
5
2
lb
kg
150
3
F
C
98.6
3
C
F
100
3
K
C
0
4
gal
l
2
4
cup
ml
1
5
1
ft
cm
6
6

# P002 unit converter: lengths, weights, temperatures and volumes, from any
# unit to any other unit of the same kind, and back again. What is typed is
# checked before anything is converted: the unit must exist and measure the
# kind chosen, and the value must be a finite number the quantity can have -
# no negative length, nothing below absolute zero.
import units
import text

def ask_unit(prompt, kind):
    # A unit of this kind, or None once the problem has been shown.
    text.trim(input(prompt)) => u
    units.kind_of(u) => k
    if k == None:
        if u == "":
            "Type a unit." ^0
        else:
            ("Unknown unit: " + u + ". " + kind + " units: " + text.join(units.symbols(kind))) ^0
        return None
    if k != kind:
        (u + " is a " + k + " unit, not a " + kind + " unit.") ^0
        return None
    return u

def ask_value(prompt, u, kind):
    # A value a quantity in unit u can have, or None once the problem has
    # been shown.
    text.trim(input(prompt)) => typed
    if typed == "":
        "Type a number." ^0
        return None
    try:
        float(typed) => x
    except ValueError:
        ("Not a number: " + typed) ^0
        return None
    if not (x - x == 0):
        ("Not a finite number: " + typed) ^0
        return None
    if x < units.lowest(u):
        if kind == "temperature":
            (text.num(x) + " " + u + " is below absolute zero (" + text.num(units.lowest(u)) + " " + u + ").") ^0
        else:
            ("A " + kind + " cannot be negative.") ^0
        return None
    return x

def convert_once(kind, last):
    # One conversion of this kind. Returns the conversion "reverse last"
    # works from next: this one, or the previous one if nothing was converted.
    (kind + " units: " + text.join(units.symbols(kind))) ^0
    ask_unit("from> ", kind) => frm
    if frm == None:
        return last
    ask_unit("to> ", kind) => to
    if to == None:
        return last
    ask_value("value in " + frm + "> ", frm, kind) => x
    if x == None:
        return last
    units.convert(x, frm, to) => y
    (text.num(x) + " " + frm + " = " + text.num(y) + " " + to) ^0
    return [x, frm, to, y]

None => last
True => running
while running:
    "" ^0
    "== Unit converter ==" ^0
    "1) length  2) weight  3) temperature  4) volume  5) reverse last  6) quit" ^0
    text.trim(input("choice> ")) => choice
    if choice == "1" or choice == "2" or choice == "3" or choice == "4":
        convert_once(units.kinds[int(choice) - 1], last) => last
    elif choice == "5":
        if last == None:
            "Nothing to reverse yet." ^0
        else:
            # From the exact result, not the six digits shown for it.
            units.convert(last[3], last[2], last[1]) => back
            (text.num(last[3]) + " " + last[2] + " = " + text.num(back) + " " + last[1]) ^0
            [last[3], last[2], last[1], back] => last
    elif choice == "6":
        False => running
    else:
        "Pick a number from 1 to 6." ^0
"Bye." ^0

import units
import text

def ask_unit(prompt, kind):
    u = text.trim(input(prompt))
    k = units.kind_of(u)
    if k == None:
        if u == "":
            print("Type a unit.")
        else:
            print("Unknown unit: " + u + ". " + kind + " units: " + text.join(units.symbols(kind)))
        return None
    if k != kind:
        print(u + " is a " + k + " unit, not a " + kind + " unit.")
        return None
    return u

def ask_value(prompt, u, kind):
    typed = text.trim(input(prompt))
    if typed == "":
        print("Type a number.")
        return None
    try:
        x = float(typed)
    except ValueError:
        print("Not a number: " + typed)
        return None
    if not x - x == 0:
        print("Not a finite number: " + typed)
        return None
    if x < units.lowest(u):
        if kind == "temperature":
            print(text.num(x) + " " + u + " is below absolute zero (" + text.num(units.lowest(u)) + " " + u + ").")
        else:
            print("A " + kind + " cannot be negative.")
        return None
    return x

def convert_once(kind, last):
    print(kind + " units: " + text.join(units.symbols(kind)))
    frm = ask_unit("from> ", kind)
    if frm == None:
        return last
    to = ask_unit("to> ", kind)
    if to == None:
        return last
    x = ask_value("value in " + frm + "> ", frm, kind)
    if x == None:
        return last
    y = units.convert(x, frm, to)
    print(text.num(x) + " " + frm + " = " + text.num(y) + " " + to)
    return [x, frm, to, y]

last = None
running = True
while running:
    print("")
    print("== Unit converter ==")
    print("1) length  2) weight  3) temperature  4) volume  5) reverse last  6) quit")
    choice = text.trim(input("choice> "))
    if choice == "1" or choice == "2" or choice == "3" or choice == "4":
        last = convert_once(units.kinds[int(choice) - 1], last)
    elif choice == "5":
        if last == None:
            print("Nothing to reverse yet.")
        else:
            back = units.convert(last[3], last[2], last[1])
            print(text.num(last[3]) + " " + last[2] + " = " + text.num(back) + " " + last[1])
            last = [last[3], last[2], last[1], back]
    elif choice == "6":
        running = False
    else:
        print("Pick a number from 1 to 6.")
print("Bye.")

# P002 unit converter - the units. Length, weight and volume convert through
# a base unit by a factor: the metre, the gram and the millilitre.
# Temperature cannot: its scales start from different zeros, so it converts
# through Celsius with an offset as well as a scale. The factors are the
# exact definitions (1 in = 2.54 cm, 1 lb = 453.59237 g, 1 US gallon =
# 3785.411784 ml), not rounded values.

["length", "weight", "temperature", "volume"] => kinds

{
    "length": ["mm", "cm", "m", "km", "in", "ft", "yd", "mi"],
    "weight": ["mg", "g", "kg", "t", "oz", "lb"],
    "temperature": ["C", "F", "K"],
    "volume": ["ml", "l", "m3", "tsp", "tbsp", "floz", "cup", "pt", "qt", "gal"],
} => unit_lists

# How many base units one unit is. The volumes from tsp on are US customary.
{
    "mm": 0.001,
    "cm": 0.01,
    "m": 1.0,
    "km": 1000.0,
    "in": 0.0254,
    "ft": 0.3048,
    "yd": 0.9144,
    "mi": 1609.344,
    "mg": 0.001,
    "g": 1.0,
    "kg": 1000.0,
    "t": 1000000.0,
    "oz": 28.349523125,
    "lb": 453.59237,
    "ml": 1.0,
    "l": 1000.0,
    "m3": 1000000.0,
    "tsp": 4.92892159375,
    "tbsp": 14.78676478125,
    "floz": 29.5735295625,
    "cup": 236.5882365,
    "pt": 473.176473,
    "qt": 946.352946,
    "gal": 3785.411784,
} => factors

def kind_of(u):
    # The kind a unit measures, or None for a unit this converter does not know.
    for k in kinds:
        if u in unit_lists[k]:
            return k
    return None

def symbols(kind):
    return unit_lists[kind]

def to_celsius(x, u):
    if u == "F":
        return (x - 32) * 5 / 9
    if u == "K":
        return x - 273.15
    return x

def from_celsius(c, u):
    if u == "F":
        return c * 9 / 5 + 32
    if u == "K":
        return c + 273.15
    return c

def convert(x, frm, to):
    # x in unit frm, expressed in unit to. Both units measure the same kind:
    # the menu checks that before it asks for a value.
    if kind_of(frm) == "temperature":
        return from_celsius(to_celsius(x, frm), to)
    return x * factors[frm] / factors[to]

def lowest(u):
    # The smallest value a quantity in unit u can have: absolute zero for a
    # temperature, nothing below zero for everything else.
    if u == "C":
        return -273.15
    if u == "F":
        return -459.67
    return 0.0

kinds = ["length", "weight", "temperature", "volume"]
unit_lists = {"length": ["mm", "cm", "m", "km", "in", "ft", "yd", "mi"], "weight": ["mg", "g", "kg", "t", "oz", "lb"], "temperature": ["C", "F", "K"], "volume": ["ml", "l", "m3", "tsp", "tbsp", "floz", "cup", "pt", "qt", "gal"]}
factors = {"mm": 0.001, "cm": 0.01, "m": 1.0, "km": 1000.0, "in": 0.0254, "ft": 0.3048, "yd": 0.9144, "mi": 1609.344, "mg": 0.001, "g": 1.0, "kg": 1000.0, "t": 1000000.0, "oz": 28.349523125, "lb": 453.59237, "ml": 1.0, "l": 1000.0, "m3": 1000000.0, "tsp": 4.92892159375, "tbsp": 14.78676478125, "floz": 29.5735295625, "cup": 236.5882365, "pt": 473.176473, "qt": 946.352946, "gal": 3785.411784}

def kind_of(u):
    for k in kinds:
        if u in unit_lists[k]:
            return k
    return None

def symbols(kind):
    return unit_lists[kind]

def to_celsius(x, u):
    if u == "F":
        return (x - 32) * 5 / 9
    if u == "K":
        return x - 273.15
    return x

def from_celsius(c, u):
    if u == "F":
        return c * 9 / 5 + 32
    if u == "K":
        return c + 273.15
    return c

def convert(x, frm, to):
    if kind_of(frm) == "temperature":
        return from_celsius(to_celsius(x, frm), to)
    return x * factors[frm] / factors[to]

def lowest(u):
    if u == "C":
        return -273.15
    if u == "F":
        return -459.67
    return 0.0

# P002 unit converter - text helpers. The interpreter that checks every
# session does not run string methods yet, so trimming and joining are
# written out here.

def trim(s):
    # s without the spaces at either end.
    0 => i
    len(s) => j
    while i < j and s[i] == " ":
        i + 1 => i
    while j > i and s[j - 1] == " ":
        j - 1 => j
    return s[i:j]

def join(words):
    # The words with one space between each two.
    "" => out
    for w in words:
        if out != "":
            out + " " => out
        out + w => out
    return out

def num(x):
    # Six significant digits, as a calculator shows them. Adding 0.0 turns
    # -0.0 into 0.0, so a typed "-0" never comes back as "-0".
    return "%g" % (x + 0.0)

def trim(s):
    i = 0
    j = len(s)
    while i < j and s[i] == " ":
        i = i + 1
    while j > i and s[j - 1] == " ":
        j = j - 1
    return s[i:j]

def join(words):
    out = ""
    for w in words:
        if out != "":
            out = out + " "
        out = out + w
    return out

def num(x):
    return "%g" % (x + 0.0)