Running Calculator — Architecture

One file, 203 lines, three functions.

main()
 ├── unit prompt        →  a chain of elif comparisons setting `unit`
 ├── time prompts       →  float/int, wrapped in try/except ValueError
 ├── conversion         →  everything to metres and seconds
 ├── calculate_distance →  metres or kilometres for display
 └── display_result     →  the output

main()

Two nested loops: an outer while run for successive runs, and inner loops for the unit and the time entry. Both inner flags are reset at the bottom so the next run starts clean.

The unit prompt is a chain of elif comparisons against lowercased input, accepting singular and plural. license, quit, and exit are handled in the same chain — which is why they are only available at that prompt and not during time entry.

Input validation

try:
    time_run = False
    length = float(input("How far did you run? "))
    hours = int(input(...))
    ...
except ValueError:
    print("Values must be in numerical form, and only seconds can be a decimal!")
    time_run = True

Catching ValueError and re-prompting is right, and the message correctly explains that only seconds may be fractional — hours and mins are parsed with int.

What is not guarded is a total time of zero, which reaches distance / time and raises ZeroDivisionError. Negative values are also accepted, producing a negative speed. See internal/known-issues.md.

Conversion

Constants at the top of main():

FT = 3.281
MILES = 1609.344
HALF_MARATHON = 21097.5
MARATHON = 42195

Each unit multiplies (or, for feet, divides) into metres. These values are correct — unlike the reference table printed on unrecognised input, which disagrees with three of them. See Units.

calculate_distance(distance, unit)

Returns metres below 1,000 and kilometres above, overwriting the unit argument it was passed. Purely for display; the speed is computed from the metre value before this is called.

display_result(...)

Prints the distance and both speeds, rounded to two places.

What is absent

No pace (minutes per kilometre or mile), no imperial output, no history, no persistence, and no argument parsing — the program is interactive only. See Roadmap.