I need a little help with a for loop in Python. At the moment, I am trying to create a random shift generator, but I also need to apply some rules on it. Right now, my function add shifts to a calendar randomly, but what I want is to add day off if the last shift was an evening shift. But I am not really sure how to interact with the previous 'i' variable in a for loop. Here is my code:

# Shift types
shifts = {
    "morning": "9:00 - 17:00",
    "evening": "16:00 - 00:00",
}

day_off = {
    "day off": "X"
}


# Schedule
schedule_ll = {
    1: [],
    2: [],
    3: [],
    4: [],
    5: [],
    6: [],
    7: [],
    8: [],
    9: [],
    10: [],
    11: [],
    12: [],
    13: [],
    14: [],
    15: [],
    16: [],
    17: [],
    18: [],
    19: [],
    20: [],
    21: [],
    22: [],
    23: [],
    24: [],
    25: [],
    27: [],
    28: [],
    29: [],
    30: [],
    31: [],
}

# Function to add shifts to schedule randomly
def start_schedule(schedule, shift, day_off):
    for i in schedule:
        schedule[i].append(random.choice(list(shift.values())))
        if schedule[i-1] == ["16:00 - 00:00"]:
            schedule[i] = list(day_off.values())
    return schedule

print(start_schedule(schedule_ll, shifts, day_off))

So when I execute this code, I receive KeyError: 0 error. I know that this error caused due to schedule[i-1], however I am not really sure how to make it work in other way. Will appreciate any help!

CodePudding user response：

You may want to treat the first element outside the loop, and then only loop over the remaining elements. Or even simpler, just change your if to

if i>1 and schedule[i-1] == ["16:00 - 00:00"]

As an aside, note that you may create your dictionary with a comprehension:

schedule = {k:[] for k in range(1,32)}

CodePudding user response：

Two recommendations:

1. Iterate over the dictionary using .items()
2. Add logic guarding against trying to access a key in schedule that does not exist prior to calling schedule[i - 1]

This makes the code a bit cleaner, prevents the function from crashing on a key error, and checks that the desired condition holds for every day except the first day.

def start_schedule(schedule, shift, day_off):
    for day, list_of_shifts in schedule.items():
        list_of_shifts.append(random.choice(list(shift.values())))
        if (i - 1) in schedule and schedule[i-1] == ["16:00 - 00:00"]:
            schedule[i] = list(day_off.values())
    return schedule