Sensible defaults

Write the codeEasy 2 stages

Most commands to the spacecraft are sent the same way: three retries, five seconds to answer. Only a few need something else, like more retries for deploying the solar array, or a short timeout for an abort, where waiting is worse than failing.

Give the uplink function sensible defaults, then add an option without touching any of its callers.

Give retries a default of 3 and timeout a default of 5.0, so the three calls below the function print:

PING (retries: 3, timeout: 5.0 s)
DEPLOY_ARRAY (retries: 5, timeout: 5.0 s)
ABORT (retries: 3, timeout: 1.0 s)

Write the defaults in the def line: def send_command(cmd, retries=3, timeout=5.0):. The calls stay as they are.

Three calls

Defaults for any call

Finish stage 1 to unlock this stage.

Abort commands need to jump the queue. Add a priority parameter with a default of "normal", show it in the line, and add a fourth call:

PING (retries: 3, timeout: 5.0 s, priority: normal)
DEPLOY_ARRAY (retries: 5, timeout: 5.0 s, priority: normal)
ABORT (retries: 3, timeout: 1.0 s, priority: normal)
ABORT (retries: 3, timeout: 1.0 s, priority: high)

Put the new parameter last, so every call written before still means the same, and add print(send_command("ABORT", priority="high", timeout=1.0)) at the bottom.

Four calls

Old calls still work

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Hints

Default Parameter Values

default-parameter-values.py

# A parameter can carry a default, used whenever you leave it out
def orbit_summary(satellite, altitude_km=550):
    return f"{satellite} at {altitude_km} km"

print(orbit_summary("Starlink-1130"))
print(orbit_summary("Sentinel-2", 786))

# Defaults let one function cover the common case and the unusual one
def link_budget(distance_au, watts=20, dish_m=70):
    return watts * dish_m / distance_au

print("Standard:", round(link_budget(1.5), 1))
print("Bigger transmitter:", round(link_budget(1.5, 100), 1))
print("Smaller dish too:", round(link_budget(1.5, 100, 34), 1))

# Defaults must come last. This would be a syntax error:
# def broken(altitude_km=550, satellite):
#     return satellite

# One strange rule: the default is built once, when def runs
def add_target(name, log=[]):
    log.append(name)
    return log

print(add_target("Vega"))
print(add_target("Altair"))


# The fix: default to None and build a fresh list inside
def add_target_safe(name, log=None):
    if log is None:
        log = []
    log.append(name)
    return log

print(add_target_safe("Vega"))
print(add_target_safe("Altair"))

Open the full example

script.py

PythonLn 1, Col 1Spaces: 4

Loading the Python environment…

Command-line arguments (sys.argv)

Separate arguments with commas. They're passed on every Run as sys.argv[1:].