single_responsibility.py

"""
Single Responsibility Principle
- A class only have one reason to change
- Separation of concerns:
    - different classes handling different, independent
      tasks/problems
"""


class Journal:
    def __init__(self):
        self.entries = []
        self.count = 0

    def add_entry(self, text):
        self.count += 1
        self.entries.append(f'{self.count}: {text}')

    def remove_entry(self, pos):
        del self.entries[pos]

    def __str__(self):
        return '\n'.join(self.entries)

# methods below give class responsibility of persistence, bad idea!

    def save(self, filename):
        file = open(filename, 'w')
        file.write(str(self))
        file.close()

    def load(self, filename):
        pass

    def load_from_web(self, url):
        pass

J = Journal()
J.add_entry('I cried today.')
J.add_entry('I ate a bug.')
print(f'Journal entries:\n{J}')


# instead, create another class to handle that responsibility
class PersistenceManager:

    @staticmethod
    def save_to_file(self, journal, filename):
        file = open(filename, 'w')
        file.write(str(self))
        file.close()

    def load(self, filename):
        pass

    def load_from_web(self, url):
        pass