adds csv task manager

learning_python3.md

@@ -1972,6 +1972,163 @@ Go back to you *currency converter* program and add a `dict` with multiple curre
 
 # Coding challenge - Task manager
 
+## CSV based task manager
+
+```python3
+import csv
+
+FILE = "mytasks.csv"
+
+def read_db():
+    db = []
+    with open(FILE, "r") as fp:
+        data = fp.readlines()
+        for task in data:
+            task = task.strip()
+            db.append(task)
+    db = [task.strip() for task in data]  # list comprehension
+    return db
+
+
+def write_db(tasks):
+    with open(FILE, "w") as fp:
+        for task in tasks:
+            fp.write("{}\n".format(task))
+
+
+def read_csv():
+    db = []
+    with open(FILE, "r") as fp:
+        reader = csv.DictReader(fp)
+        for item in reader:
+            db.append(item)
+    return db
+
+
+def write_csv(tasks):
+    with open(FILE, "w") as fp:
+        keys = tasks[0].keys()
+        writer = csv.DictWriter(fp, keys)
+        writer.writeheader()
+        for task in tasks:
+            writer.writerow(task)
+
+
+def delete_task(index, task_list):
+    if index <= len(task_list):
+        task = task_list.pop(index)
+        print("deleting: {}".format(task))
+    else:
+        print("cannot find your task")
+
+
+def mark_task_done(index, task_list):
+    if index <= len(task_list):
+        task = task_list[index]
+        task["done"] = "0"
+        print("marking done: {}".format(task["description"]))
+
+
+def add_task(task, task_list):
+    task_list.append(task)
+    print("you now have {} tasks to do...".format(len(task_list)))
+
+
+def show_tasks(task_list):
+    for task in task_list:
+        if task["done"] == "0":
+            continue
+        index = task_list.index(task)
+        key = "description"
+        print("\t{}:\t{}:\t{}".format(index, key, task[key]))
+        key = "priority"
+        print("\t\t{}:\t\t{}".format(key, task[key]))
+    print("<--")
+
+# interface
+
+def ask_for_action():
+    print("what do you want to do?")
+    print("1. add a task")
+    print("2. delete a task")
+    print("3. mark task done")
+    print("4. show all tasks")
+    print("5. save and quit")
+    while True:
+        action = input("--> ")
+        if action.isdigit():
+            action = int(action)
+            break
+        print("please input a number...")
+    return action
+
+
+def ask_for_index():
+    while True:
+        index = input("which index do you want? ")
+        if index.isdigit():
+            index = int(index)
+            break
+        print("only digits please...")
+    return index
+
+
+def ask_for_priority():
+    while True:
+        index = input("which priority should the task have? ")
+        if index.isdigit():
+            index = int(index)
+            break
+        print("only digits please...")
+    return index
+
+
+def ask_for_description():
+    min = 5
+    while True:
+        description = input("what do you have to do? ")
+        if len(description) >= min:
+            break
+        print("description needs to be longer than {} characters".format(min))
+    return description
+
+
+def main():
+    tasks = read_db()
+    tasks = read_csv()
+    while True:
+        action = ask_for_action()
+        if action == 1:
+            description = ask_for_description()
+            priority = ask_for_priority()
+            task = {
+                "description": description,
+                "done": "1",
+                "priority": priority,
+            }
+            add_task(task, tasks)
+        elif action == 2:
+            show_tasks(tasks)
+            index = ask_for_index()
+            delete_task(index, tasks)
+            show_tasks(tasks)
+        elif action == 3:
+            show_tasks(tasks)
+            index = ask_for_index()
+            mark_task_done(index, tasks)
+            show_tasks(tasks)
+        elif action == 4:
+            show_tasks(tasks)
+        elif action == 5:
+            write_csv(tasks)
+            print("bye bye!")
+            exit()
+
+
+if __name__ == "__main__":
+    main()
+```
+
 Can you create me a *task manager* please?
 I made one that is run from the command line with different arguments to modify it's behaviour.
 If this looks too challenging I can tell you that the *full code* is 64 lines long, including empty lines!