Make a web framework with python

Part 4

Part 1
Part 2
Part 3’s features were:

• Raising error when routing existing route
• Making simple Template engine

In part 4, we will add one feature:

• Making our own database manager for our framework

Now, let’s create a class called Database:

class Database:
  def __init__(self, database_file):
        self.__database = []
        current_line = []
        for line in open(database_file).read().split('\n'):
            for column in line.split(' '):
                current_line.append(column)
            self.__database.append(current_line)
            current_line = []
    self.__file = database_file

Simple, right? We just created a variable called database, which will be representing our
database. We then created a local variable called current_line which will be handy soon.
Now, there is a for loop that says “for line in open(database_file).read().split(‘\n’)”, which is all
self-explainatory. Also, there is a nested for loop which loops through the line split by a
space, and inside this you append the column to the current line. After looping through all the columns,
We append the current line to self.__database, and finally we reset current_line to an empty list.
Whew! Now that we got this, let’s make a get_row and a get_column method to get the rows in the
database and to get the columns in a row in the database:

class Database:
  def __init__(self, database_file):
        self.__database = []
        current_line = []
        for line in open(database_file).read().split('\n'):
            for column in line.split(' '):
                current_line.append(column)
            self.__database.append(current_line)
            current_line = []
    self.__file = database_file
    
  def get_row(self, row):
    return self.__database[row - 1]  # Why did I subtract it by one? To support indexing!
    
  def get_column(self, row, column):
    return self.get_row(row)[column - 1]  # Following the DRY principle here

Great job!
For an exercise, make some methods to add rows and columns.
Done? Here’s the solution:

class Database:
  def __init__(self, database_file):
        self.__database = []
        current_line = []
        for line in open(database_file).read().split('\n'):
            for column in line.split(' '):
                current_line.append(column)
            self.__database.append(current_line)
            current_line = []
    self.__file = database_file
    
  def get_row(self, row):
    return self.__database[row - 1]  # Why did I subtract it by one? To support indexing!
    
  def get_column(self, row, column):
    return self.get_row(row)[column - 1]  # Following the DRY principle here
    
  def add_row(self, row, row_contents):
    self.__database.insert(row - 1, row_contents)
    
  def add_column(self, row, column, column_value):
    self.__database[row - 1].insert(column - 1, column_value)

Ok, let’s make some handy methods to remove either a row or a column:

class Database:
  def __init__(self, database_file):
        self.__database = []
        current_line = []
        for line in open(database_file).read().split('\n'):
            for column in line.split(' '):
                current_line.append(column)
            self.__database.append(current_line)
            current_line = []
    self.__file = database_file
    
  def get_row(self, row):
    return self.__database[row - 1]  # Why did I subtract it by one? To support indexing!
    
  def get_column(self, row, column):
    return self.get_row(row)[column - 1]  # Following the DRY principle here
    
  def add_row(self, row, row_contents):
    self.__database.insert(row - 1, row_contents)
    
  def add_column(self, row, column, column_value):
    self.__database[row - 1].insert(column - 1, column_value)
    
  def remove_row(self, row):
    del self.__database[row - 1]
    
  def remove_column(self, row, column):
    del self.__database[row - 1][column - 1]

After we do that, let’s discuss.
What if you want to get the unsaved changes, as a string?
Let’s do just that!

class Database:
  def __init__(self, database_file):
        self.__database = []
        current_line = []
        for line in open(database_file).read().split('\n'):
            for column in line.split(' '):
                current_line.append(column)
            self.__database.append(current_line)
            current_line = []
    self.__file = database_file
    
  def get_row(self, row):
    return self.__database[row - 1]  # Why did I subtract it by one? To support indexing!
    
  def get_column(self, row, column):
    return self.get_row(row)[column - 1]  # Following the DRY principle here
    
  def add_row(self, row, row_contents):
    self.__database.insert(row - 1, row_contents)
    
  def add_column(self, row, column, column_value):
    self.__database[row - 1].insert(column - 1, column_value)
    
  def remove_row(self, row):
    del self.__database[row - 1]
    
  def remove_column(self, row, column):
    del self.__database[row - 1][column - 1]
    
  def get_unsaved_changes(self):
    unsaved_changes = ''
    for line in self.__database:
      unsaved_changes += ' '.join(line)  # Joining line items with a space in between them
    return unsaved_changes

Wouldn’t it be easier to just call a method to get the current contents of the database,
instead of having to do the built-in open function all over again?
We will do this:

class Database:
  def __init__(self, database_file):
        self.__database = []
        current_line = []
        for line in open(database_file).read().split('\n'):
            for column in line.split(' '):
                current_line.append(column)
            self.__database.append(current_line)
            current_line = []
    self.__file = database_file
    
  def get_row(self, row):
    return self.__database[row - 1]  # Why did I subtract it by one? To support indexing!
    
  def get_column(self, row, column):
    return self.get_row(row)[column - 1]  # Following the DRY principle here
    
  def add_row(self, row, row_contents):
    self.__database.insert(row - 1, row_contents)
    
  def add_column(self, row, column, column_value):
    self.__database[row - 1].insert(column - 1, column_value)
    
  def remove_row(self, row):
    del self.__database[row - 1]
    
  def remove_column(self, row, column):
    del self.__database[row - 1][column - 1]
    
  def get_unsaved_changes(self):
    unsaved_changes = ''
    for line in self.__database:
      unsaved_changes += ' '.join(line)  # Joining line items with a space in between them
    return unsaved_changes
    
  def get(self):
    return open(self.__file).read()

Oh, two more methods before the last method!
Let’s make these awesome methods to empty the database, and another to empty unsaved changes!

class Database:
  def __init__(self, database_file):
        self.__database = []
        current_line = []
        for line in open(database_file).read().split('\n'):
            for column in line.split(' '):
                current_line.append(column)
            self.__database.append(current_line)
            current_line = []
    self.__file = database_file
    
  def get_row(self, row):
    return self.__database[row - 1]  # Why did I subtract it by one? To support indexing!
    
  def get_column(self, row, column):
    return self.get_row(row)[column - 1]  # Following the DRY principle here
    
  def add_row(self, row, row_contents):
    self.__database.insert(row - 1, row_contents)
    
  def add_column(self, row, column, column_value):
    self.__database[row - 1].insert(column - 1, column_value)
    
  def remove_row(self, row):
    del self.__database[row - 1]
    
  def remove_column(self, row, column):
    del self.__database[row - 1][column - 1]
    
  def get_unsaved_changes(self):
    unsaved_changes = ''
    for line in self.__database:
      unsaved_changes += ' '.join(line)  # Joining line items with a space in between them
    return unsaved_changes
    
  def get(self):
    return open(self.__file).read()
    
  def empty_database(self):
    open(self.__file, 'w').write('')  # We changed all file contents to ''
    
  def empty_unsaved_changes(self):
    self.__database = []  # We changed self.__database to an empty list

Now, our last method will be save_changes: To save the unsaved changes to the database.
Let’s discuss and then do.
So, our plan is to loop through self.__database, and inside the loop we will join it to the
contents to add.

class Database:
  def __init__(self, database_file):
        self.__database = []
        current_line = []
        for line in open(database_file).read().split('\n'):
            for column in line.split(' '):
                current_line.append(column)
            self.__database.append(current_line)
            current_line = []
    self.__file = database_file
    
  def get_row(self, row):
    return self.__database[row - 1]  # Why did I subtract it by one? To support indexing!
    
  def get_column(self, row, column):
    return self.get_row(row)[column - 1]  # Following the DRY principle here
    
  def add_row(self, row, row_contents):
    self.__database.insert(row - 1, row_contents)
    
  def add_column(self, row, column, column_value):
    self.__database[row - 1].insert(column - 1, column_value)
    
  def remove_row(self, row):
    del self.__database[row - 1]
    
  def remove_column(self, row, column):
    del self.__database[row - 1][column - 1]
    
  def get_unsaved_changes(self):
    unsaved_changes = ''
    for line in self.__database:
      unsaved_changes += ' '.join(line)  # Joining line items with a space in between them
    return unsaved_changes
    
  def get(self):
    return open(self.__file).read()
    
  def empty_database(self):
    open(self.__file, 'w').write('')  # We changed all file contents to ''
    
  def empty_unsaved_changes(self):
    self.__database = []  # We changed self.__database to an empty list
    
  def save_changes(self, replace_db_contents=True):
    new_contents = ''
    for line in self.__database:
      new_contents += ' '.join(line) + '\n'
    contents_before = ''
    if replace_db_contents is True:
      pass
    else:
      contents_before = self.get()
    open(self.__file, 'w').write(contents_before + new_contents)

🥳 YAY! We just made a web framework—with no 3rd-party libraries—and it’s from scratch! This
must be a day of celebration!

Conclusion

This is the ending part for this series. I hope you liked it!