Creating ICS calendar events from JSON-like file

the purpose of this code is to take a Taskwarrior (it’s a todo list application) server file that is mostly JSON and create unique ICS calendar events. The logic mostly works: I still see some duplicates that I can weed out, but doing that isn’t what I’m looking for in this review. The purpose of this code review is my coding style, readability, and efficiency. I’m new to python (but please be critical – I want to get better) so I’m sure I’m doing some strange things. This script is meant to be called from a Unix cron job.

#!/usr/bin/env python3

import os.path
from ics import Calendar, Event
import json
import sys
import os
import io

taskwarrior_formatted_data_location = "/var/taskd/tx.data"
ics_calendar_full_path = "/var/www/html/tasks.ics"
ics_calendar_full_path_chores = "/var/www/html/chores.ics"
ics_calendar_full_path_announcements = "/var/www/html/announcements.ics"
unique_list_of_calendar_tasks = []

valid_statuses_for_calendar = ['pending', 'waiting']
invalid_statuses_for_calendar = ['completed', 'deleted']


def create_uniqueness(task):
    """ creates a definition of uniqueness from a task's attributes
       input: task: an object with a Taskwarrior set of attributes
       output: a string of the unique signature of this task """

    if not task:
        return None

    if task.get('due') and task.get('description'):
        return task['due'] + task['description']
    else:
        return task['uuid']


def is_unique_calendar_task(task):
    """ if this task exists in the list of tasks to make a calendar already
       input: task: an object with a Taskwarrior set of attributes
       output: boolean - true if the task is unique, false if it already existed in the list """

    if not task:
        return None
    if task['status'] in invalid_statuses_for_calendar:
        return False

    if task.get('status') and task['status'] in valid_statuses_for_calendar:
        unique_task_id = create_uniqueness(task)
        if unique_task_id in unique_list_of_calendar_tasks:
            return False
        unique_list_of_calendar_tasks.append(unique_task_id)
        return True
    return False


def create_task_calendar_description(task):
    """ creates a custom description of the task for the calendar summary
       input: task: an object with a Taskwarrior set of attributes
       output: string to be used for the calendar event summary """
    project = "{} {} {}".format("[", task['project'], "] ") if task.get('project') else ""
    tags = " [" + ", ".join([k for k in task['tags'] if 'cal.' not in k]) + "]" if (task.get('tags') and [k for k in
           task['tags'] if 'cal.' not in k]) else ""
    return project + task['description'] + tags


def get_task_first_calendar(task):
    """ find the first cal.<xyz> tag, which indicates which calendar this task should appear on. Defaults to the
    general calendar
       input: task: an object with a Taskwarrior set of attributes
       output: string with the name of the calendar this event should go on """
    if task.get('tags') is None:
        return ""
    cals = [s for s in task['tags'] if 'cal.' in s]
    if not cals:
        return ""
    return cals[0].replace("cal.", "")


def get_unique_task():
    """ read the JSON-like file, filtering out lines I don't need, and calling the unique function to create tasks to
    be processed
       input: none
       output: yields a unique task """
    real_lines = []
    for line in io.open(taskwarrior_formatted_data_location, 'r', encoding='utf8'):
        li = line.strip()
        if li.startswith("{"):
            real_lines.append(li)

    lines_as_string = "[" + ",".join(real_lines) + "]"
    for task in json.loads(lines_as_string):
        if is_unique_calendar_task(task):
            yield task


def get_task_start_date_for_event(task):
    """ find the calendar event start date based on a hierarchy of which date to use
       input: task: an object with a Taskwarrior set of attributes
       output: date to use in Taskwarrior format """
    if task is None:
        return ""
    if task.get('due'):
        return task['due']
    if task.get('scheduled'):
        return task['scheduled']
    if task.get('wait'):
        return task['wait']
    else:
        return ""


if __name__ == "__main__":
    general_cal = Calendar(creator="My TaskWarrior Calendar")
    chores_cal = Calendar(creator="My TaskWarrior Chores Calendar")
    ann_cal = Calendar(creator="My TaskWarrior Announcements Calendar")
    for task in get_unique_task():

        event_due = get_task_start_date_for_event(task)
        if event_due in (None, ""):
            continue
        cal_event = Event()
        cal_event.begin = event_due
        cal_event.name = create_task_calendar_description(task)


        task_first_calendar = get_task_first_calendar(task)
        if task_first_calendar == "":
            general_cal.events.append(cal_event)
        if task_first_calendar == "chores":
            chores_cal.events.append(cal_event)
        if task_first_calendar == "announcements":
            ann_cal.events.append(cal_event)


    with open(os.path.expanduser(ics_calendar_full_path), 'w') as f:
        f.writelines(general_cal)

    with open(os.path.expanduser(ics_calendar_full_path_chores), 'w') as f:
        f.writelines(chores_cal)

    with open(os.path.expanduser(ics_calendar_full_path_announcements), 'w') as f:
        f.writelines(ann_cal)

    sys.exit(0)

Thanks in advance for your feedback.

• Do not mix standard library and third party imports.
• As you’re using Python 3 use function and variable annotations instead of defining types in docstrings. Docstrings are fine but they become outdated too soon. With annotation the advantage is that you can use static analyzers like Mypy to crosscheck.
• unique_list_of_calendar_tasks = []: unique_list sounds like a set.
• io.open is not required in Python 3. The builtin open() is fine unless you want to write Python 2/3 compatible code.
• Do not maintain unique tasks in a global variable, you can easily move it under get_unique_tasks.
• You seem to be doing a lots of processing related to a task, perhaps create a Task class that encapsulates these methods.

from typing import Any, Dict, Iterator

class Task:
    def __init__(self, data: Dict[Any, Any]) -> None:
        self.data = data

    @property
    def id(task) -> str:
        if task.get('due') and task.get('description'):
            return task['due'] + task['description']
        return task['uuid']

    @property
    def is_valid(self) -> bool:
        if self.data['status'] in invalid_statuses_for_calendar:
            return False

        if not (self.data.get('status') or self.data['status'] in valid_statuses_for_calendar):
            return False
        return True

    @property
    def first_calendar(self) -> str:
        if self.data.get('tags') is None:
            return ""
        cal = next((s for s in self.data['tags'] if 'cal.' in s), None)
        if cal is None:
            return ""
        return cal.replace("cal.", "")

    @property
    def start_date_for_event(self) -> str:
        if self.data.get('due'):
            return self.data['due']
        if self.data.get('scheduled'):
            return self.data['scheduled']
        if self.data.get('wait'):
            return self.data['wait']
        else:
            return ""

    def __str__(self):
        project = "{} {} {}".format("[", self.data['project'], "] ") if self.data.get('project') else ""
        tags = " [" + ", ".join([k for k in self.data['tags'] if 'cal.' not in k]) + "]" if (self.data.get('tags') and [k for k in
            self.data['tags'] if 'cal.' not in k]) else ""
        return project + self.data['description'] + tags

    def __eq__(self, other):
        if isinstance(other, Task):
            return self.id == other.id
        return NotImplemented

    def __hash__(self):
        return hash(self.id)


def get_unique_tasks() -> Iterator[Dict[Any, Any]]:
    real_lines = []
    for line in open(taskwarrior_formatted_data_location, 'r', encoding='utf8'):
        li = line.strip()
        if li.startswith("{"):
            real_lines.append(li)

    lines_as_string = "[" + ",".join(real_lines) + "]"
    tasks = set()
    for row in json.loads(lines_as_string):
        task = Task(row)
        if task not in tasks and task.is_valid:
            yield task
            tasks.add(task)

if __name__ == "__main__":

    general_cal = Calendar(creator="My TaskWarrior Calendar")
    chores_cal = Calendar(creator="My TaskWarrior Chores Calendar")
    ann_cal = Calendar(creator="My TaskWarrior Announcements Calendar")

    for task in get_unique_task():
        event_due = task.start_date_for_event
        if not event_due:
            continue
        cal_event = Event()
        cal_event.begin = event_due
        cal_event.name = str(task)

        task_first_calendar = task.first_calendar

        if task_first_calendar == "":
            general_cal.events.append(cal_event)
        if task_first_calendar == "chores":
            chores_cal.events.append(cal_event)
        if task_first_calendar == "announcements":
            ann_cal.events.append(cal_event)


    with open(os.path.expanduser(ics_calendar_full_path), 'w') as f:
        f.writelines(general_cal)

    with open(os.path.expanduser(ics_calendar_full_path_chores), 'w') as f:
        f.writelines(chores_cal)

    with open(os.path.expanduser(ics_calendar_full_path_announcements), 'w') as f:
        f.writelines(ann_cal)

    sys.exit(0)

• In the above code Task is now a class whose instances are also hashable, hence you can also store unique tasks in a set.

• create_task_calendar_description is now the __str__ representation of the task.

• create_uniqueness has been replaced with id property.
• is_unique_calendar_task has been removed and instead we use task’s id and id_valid properties to identify whether we want to process it or not.
• We are no longer maintaining unique tasks in a global list, instead we are now using a set in get_unique_tasks to keep track of already processed(and valid) tasks. You could also change the logic here to just store just the task’s id in set.