Custom exceptions in a library

custom_exceptions.py

# exceptions.py
class ProblemError(Exception):
    """An exception raised during problem specification"""


class ShiftError(ProblemError):
    """Some aspect of the shift pattern definition is invalid"""
    
# shifts.py (collected exceptions from the module)
raise ShiftError("No hours are registered for this shift")
raise ShiftError("The shift day does not start at midnight")
raise ShiftError(
    (
        "Non-contiguous shift block encountered between: "
        f"{self.periods[i]} and {self.periods[i + 1]}"
    ).lstrip()
)
raise ShiftError(
    (
        "The following shift does not run until midnight: "
        f"{self.periods[-1]['end']}"
    ).lstrip()
)
raise ShiftError(
    (
        "The date of the first shift activity of this pattern "
        "does not match the reference start date. If no shift "
        "activity is planned for this day, use `add_downday()`"
        " to fill in any gaps."
    ).lstrip()
)
raise ShiftError("Shift pattern is not contiguous in days")
raise ShiftError("Shift pattern has not been built")