Temperature unit converter in Python

Question

I am starting to learn python and this has been my first project but I am not entirely happy, I think it could be done better. Could you help me? The strings are in Spanish but I think it does not harm understanding.

 elegir_magnitud = int(input(
"""1 = Temperatura
2 = Longitud 
3 = Masa
4 = Volumen
5 = Tiempo
6 = Divisa
Entra número deseado: """))
if elegir_magnitud == 1 :
 unidad_temperatura = int(input(
 """ 
------------------Elige la unidad de temperatura a ser convertida:---------------
1 = Celsius
2 = Farhengei o como se escriba
3 = Kelvin
Entra número deseado: """))
 cantidad_temperatura = float(input(
 """
Entra la cántidad de esa unidad deseada: """))
#ELEGIR UNIDAD DE TEMPERATURA A CONVERTIR
 unidad_a_convertir = int(input(
 """ 
--------------------Elige la unidad de temperatura a convertir:-----------------
1 = Celsius
2 = Farhengei o como se escriba
3 = Kelvin
Entra número deseado: """))
 if unidad_temperatura == unidad_a_convertir:
 print("Por qué quieres convertir a la misma unidad?")
 if unidad_temperatura == 1 and unidad_a_convertir == 3:
 print("""El resultado de la conversion es: \n""",float(cantidad_temperatura - 273),"oK")
 if unidad_temperatura == 1 and unidad_a_convertir == 2:
 print("""El resultado de la conversion es: \n""",float(cantidad_temperatura * 9%5 +32),"oF")
 if unidad_temperatura == 3 and unidad_a_convertir == 1:
 print("""El resultado de la conversion es: \n""",float(cantidad_temperatura + 273),"oC")
 if unidad_temperatura == 3 and unidad_a_convertir == 2:
 print("""El resultado de la conversion es: \n""",float((cantidad_temperatura -273) * 9 % 5 + 32),"oF")
 if unidad_temperatura == 2 and unidad_a_convertir == 3:
 print("""El resultado de la conversion es: \n""",float((cantidad_temperatura - 32) % 9 * 5 - 273),"oK")
 if unidad_temperatura == 2 and unidad_a_convertir == 1:
 print("""El resultado de la conversion es: \n""",float(cantidad_temperatura % 9*5 -32),"oC")

Answer 1

Localisation

The strings are in Spanish

Great! However, that's not the only thing in Spanish: your variables (elegir_magnitud, unidad_temperatura, etc.) are as well.

This is non-ideal for at least a couple of reasons:

• Python, being a language whose syntax is written in English, conflicts with your code that is then a mixture of English and Spanish. This is inconsistent.
• For better or worse, the de-facto language of software development is English. Particularly for international collaboration or online open-source development, it is important to use a language that is accessible to more people.

It's a wonderful thing to apply internationalization (i18n) to your strings, but it should be to your strings only, and not the code.

Factor out common code

Consider refactoring your code to:

• Have only one method that asks for units, called twice (once for source unit and once for destination unit)
• Make a tuple of coefficient-offset pairs. These represent the linear function from the given unit to Kelvin and back. This will only need two unit conversion formulae, rather than (worst-case) 2^n with the current strategy.

Bug?

Are you sure that this works?

cantidad_temperatura % 9*5 -32

I doubt that modulus is the right thing to do here. You should be using division /.

Example code

Notes:

• This does a rough i18n, with some strings from Google Translate (so my apologies for the likely poor Spanish).
• Only English and Spanish are implemented but any other language can be added.
• This assumes that your operating system is set to the correct locale
• For these purposes, only the ISO639-1 language without country code is considered
• Enums are used for stricter type assurance
• Type hints are used for better static analysis and documentation
• I have not bothered to add the complexity of input validation, so if input is invalid, there will be an exception thrown
• Note the use of locale methods rather than direct int and float construction and formatting

strings.py

from locale import getlocale, getdefaultlocale
# For testing only
# from locale import setlocale, LC_ALL
# setlocale(LC_ALL, 'es_ES.UTF8')
def get_lang() -> str:
 lang, _ = getlocale()
 def_lang, _ = getdefaultlocale()
 return (lang or def_lang)[:2]
LANG = get_lang()
if LANG == 'en':
 DIMENSIONS = (
 'Temperature',
 'Length',
 'Mass',
 'Volume',
 'Time',
 'Currency',
 )
 TEMP_UNITS = (
 'Kelvin',
 'Celsius',
 'Fahrenheit',
 )
 ENTER_NUMBER = 'Enter the desired number: '
 CHOOSE_TEMP_SOURCE = 'Choose the source temperature unit to convert: '
 CHOOSE_TEMP_DEST = 'Choose the destination temperature unit to convert: '
 PROVIDE_TEMP = 'Provide the source temperature: '
 RESULT = 'The result of the conversion is:'
elif LANG == 'es':
 DIMENSIONS = (
 'Temperatura',
 'Longitud',
 'Masa',
 'Volumen',
 'Tiempo',
 'Divisa'
 )
 TEMP_UNITS = (
 'Kelvin',
 'Centígrada',
 'Fahrenheit'
 )
 ENTER_NUMBER = 'Entra número deseado: '
 CHOOSE_TEMP_SOURCE = 'Elija la unidad de temperatura fuente para convertir: '
 CHOOSE_TEMP_DEST = 'Elija la unidad de temperatura de destino para convertir: '
 PROVIDE_TEMP = 'Proporcionar la temperatura de la fuente: '
 RESULT = 'El resultado de la conversión es:'

convert.py

from enum import Enum
from locale import format_string, atof, atoi
from typing import TypeVar, Type, Iterable
from strings import *
class Dimension(Enum):
 TEMPERATURE = 1
 LONGITUDE = 2
 MASS = 3
 VOLUME = 4
 TIME = 5
 CURRENCY = 6
class TempUnit(Enum):
 KELVIN = 1
 CELSIUS = 2
 FAHRENHEIT = 3
# To get from this unit to Kelvin:
# kelvin = m * this_unit + b
TEMP_PARAMETERS = {
 # This unit m b
 TempUnit.KELVIN: (1, 0),
 TempUnit.CELSIUS: (1, 273.16),
 TempUnit.FAHRENHEIT: (5/9, 273.16 - 5/9*32),
}
InputEnum = TypeVar('InputEnum', bound=Enum)
def enum_from_input(t_enum: Type[InputEnum], labels: Iterable[str]) -> InputEnum:
 print(
 '\n'.join(
 format_string('%d = %s', (enum.value, label))
 for enum, label in zip(t_enum, labels)
 )
 )
 result = t_enum(atoi(input(ENTER_NUMBER)))
 print()
 return result
def main():
 dimension = enum_from_input(Dimension, DIMENSIONS)
 if dimension != Dimension.TEMPERATURE:
 raise NotImplementedError()
 print(CHOOSE_TEMP_SOURCE)
 source = enum_from_input(TempUnit, TEMP_UNITS)
 print(CHOOSE_TEMP_DEST)
 dest = enum_from_input(TempUnit, TEMP_UNITS)
 temp1 = atof(input(PROVIDE_TEMP))
 # Use a simple linear transformation where y = mx + b; first convert to
 # the base unit (Kelvin)
 m, b = TEMP_PARAMETERS[source]
 kelvin = m*temp1 + b
 # Now calculate inverse to the destination unit
 m, b = TEMP_PARAMETERS[dest]
 temp2 = (kelvin - b)/m
 print(format_string('%s %.1f', (RESULT, temp2)))
if __name__ == '__main__':
 main()

Example output

1 = Temperatura
2 = Longitud
3 = Masa
4 = Volumen
5 = Tiempo
6 = Divisa
Entra número deseado: 1
Elija la unidad de temperatura fuente para convertir: 
1 = Kelvin
2 = Centígrada
3 = Fahrenheit
Entra número deseado: 3
Elija la unidad de temperatura de destino para convertir: 
1 = Kelvin
2 = Centígrada
3 = Fahrenheit
Entra número deseado: 2
Proporcionar la temperatura de la fuente: 81
El resultado de la conversión es: 27,2