Shortening an if, elif, elif else clause

I am making a program that checks when the next train leaves. For that, it takes the departure times from a website and stores them in arrays(times_luz and times_hitz).

However, the API sometimes doesn't have any Information, so there's no data in the array which, later in the code, leads to an error, Therefore I thought this would be a good Idea:

if times_hitz and times_luz:
Code to be executed if both contain values

elif times_luz:
Code to be executed if only times_luz contains values

elif times_hitz:
Code to be executed if only times_hitz contains values

else
print("No content available")
sys.exit()


This would technically work, but the code is currently about 30 lines long so I would have to Copy & Paste that Code 2 times with only slight changes. This would lead to about 80 lines of code and would look pretty ugly. Is there any better way of doing this?

Edit:

I made a huge mistake in guessing the size of my file, it's actually 103 lines long, including comments. Therefore, I decided to upload it to google drive:

https://drive.google.com/open?id=1F5FIuAy_g7sC_2wTprqg3EF_m_JXEreL

The error that occurs when there's no data in the array is on line 44 and 48 because the 1st item in the Array times_luz/hitz doesn't exist and can therefore not be saved to a variable. This means that I have to execute some code that only checks the _luz trains if there's nothing in times_hitz and the other way around. If both contain data, I want to execute the code I have on google drive and if neither contains data, it should print an error message.

The endings _luz and _hitz stand for Lucerne and Hitzkirch, the two ways a train can go at my station

This code basically takes times from a Train API and stores them in 3 different variables. It then checks the 3 times and stores the one that will depart next in a variable. It does this for _luz and _hitz. In the end, it checks which train(_luz or _hitz) departs earlier and prints the difference between datetime.now and the train departure time

Sorry if my explanation is unclear, feel free to ask more questions in the comments

def f(times_hitz, times_luz):

None

None

times_hitz or

times_hitz = times_hitz if times_hitz else

if/elif

2 Answers
2

There is some massive duplication in your code. Basically, the entire code for getting the next train is the same for the two destination (and any other destinations you might add later) and should be moved to a function.

def get_next_train(params):
res =requests.get(base, params=params)
parsed_json = res.json()

#Zeiten aus parsed_json extrahieren
time_strings = [d["from"]["prognosis"]["departure"]
for d in parsed_json["connections"]]

#String, um Zeiten in time_strings nach ISO 8601 zu parsen
iso_format = "%Y-%m-%dT%H:%M:%S%z"

# Time Strings zu datetime Objekten konvertieren
times = [datetime.strptime(ts, iso_format)
for ts in time_strings if ts is not None]

# Checken, ob times leer sind
if not times:
return None # CHANGE: return None if no times found

#Zeitzone der ersten zeit in Times speichern
tz = times[0].tzinfo

#jetztige Zeit mit Zeitzone tz, Mikrosekunden löschen
nowtime = datetime.now(tz).replace(microsecond=0)

# Checken, ob Time_1 noch in der Zukunft ist. Wenn ja, diese Zeit als Time_luz speichern
time = min(t for t in times[0:3] if t > nowtime) # CHANGE: use min
return time, time - nowtime


Then, you can get the results for the two destinations, and get the min after filtering results that are None, then just check whether that min is None (the default).

min

filter

None

None

res_luz = get_next_train(params_luz)
res_hitz = get_next_train(params_hitz)
res = min(filter(None, (res_luz, res_hitz)), default=None)
if res is not None:
time, diff = res
print ("Next train", time, ", in", str(diff))
else:
print("Service nicht verfügbar")


Update: It seems like late in the evening, there might be no train departing after nowtime, causing the min to raise an exception. You can fix this by providing another default like below and returning None in this case, too.

nowtime

min

default

None

time = min((t for t in times if t > nowtime), default=None)
return (time, time - nowtime) if time is not None else None


Update: If you want to know the destination of the next train (makes sense...) you can get it from the parameters and return it alongside the time and diff.

return time, time - nowtime, params["to"]


then unpack and print it:

if res is not None:
time, diff, dest = res
print ("Next train to %s at %s (in %s)" % (dest, time, diff))


times[0:3]

nowtime

default=None

if time_luz < time_hitz print("Train to Lucerne departs in", diff)

if time_hitz < time_luz print("Train to Hitzkirch departs in", diff)

you can instead make a definition in Python instead, so you define it once. And where ever you need to use this definition again, you can simply call it. You can also make it a class once this function gets more complicated.

Your code will be this instead:

def train_time(times_hitz, time_luz):
if times_hitz and times_luz:
Code to be executed if both contain values

elif times_luz:
Code to be executed if only times_luz contains values

elif times_hitz:
Code to be executed if only times_hitz contains values

else:
print("No content available")
sys.exit()

return leave


Where the "leave" will be from your executed code to determine when the next train leaves. And whenever you need to evaluate if the train is leaving, simply do:

leave = train_time(times_hitz, time_luz)


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