We will often want to save our Python classes, for use in multiple Notebooks.
We can do this by writing text files with a .py extension, and then
You can also maintain your library code in a Notebook, and use
%%writefile to create your library, though this is not encouraged!
Libraries are usually structured with multiple files, one for each class.
We will be turning the code we have written for the maze into a library, so that other code can reuse it.
We group our modules into packages, by putting them together into a folder. You can do this with explorer, or using a shell, or even with Python:
import os if 'mazetool' not in os.listdir(os.getcwd()): os.mkdir('mazetool')
%%writefile mazetool/maze.py from .room import Room from .person import Person class Maze(object): def __init__(self, name): self.name = name self.rooms =  self.occupants =  def add_room(self, name, capacity): result = Room(name, capacity) self.rooms.append(result) return result def add_exit(self, name, source, target, reverse= None): source.add_exit(name, target) if reverse: target.add_exit(reverse, source) def add_occupant(self, name, room): self.occupants.append(Person(name, room)) room.occupancy += 1 def wander(self): "Move all the people in a random direction" for occupant in self.occupants: occupant.wander() def describe(self): for occupant in self.occupants: occupant.describe() def step(self): house.describe() print() house.wander() print() def simulate(self, steps): for _ in range(steps): self.step()
%%writefile mazetool/room.py from .exit import Exit class Room(object): def __init__(self, name, capacity): self.name = name self.capacity = capacity self.occupancy = 0 self.exits =  def has_space(self): return self.occupancy < self.capacity def available_exits(self): return [exit for exit in self.exits if exit.valid() ] def random_valid_exit(self): import random if not self.available_exits(): return None return random.choice(self.available_exits()) def add_exit(self, name, target): self.exits.append(Exit(name, target))
%%writefile mazetool/person.py class Person(object): def __init__(self, name, room = None): self.name=name self.room=room def use(self, exit): self.room.occupancy -= 1 destination=exit.target destination.occupancy +=1 self.room=destination print(self.name, "goes", exit.name, "to the", destination.name) def wander(self): exit = self.room.random_valid_exit() if exit: self.use(exit) def describe(self): print(self.name, "is in the", self.room.name)
%%writefile mazetool/exit.py class Exit(object): def __init__(self, name, target): self.name = name self.target = target def valid(self): return self.target.has_space()
In order to tell Python that our "mazetool" folder is a Python package,
we have to make a special file called
__init__.py. If you import things in there, they are imported as part of the package:
%%writefile mazetool/__init__.py from .maze import Maze # Python 3 relative import
In this case we are making it easier to import
Maze as we are making it available one level above.
We just wrote the files, there is no "Maze" class in this notebook yet:
myhouse = Maze('My New House')
--------------------------------------------------------------------------- NameError Traceback (most recent call last) Cell In, line 1 ----> 1 myhouse = Maze('My New House') NameError: name 'Maze' is not defined
But now, we can import Maze, (and the other files will get imported via the chained Import statements, starting from the
Let's see how we can access the files we created:
from mazetool import Maze
house = Maze('My New House') living = house.add_room('livingroom', 2)
Note the files we have created are on the disk in the folder we made:
os.listdir(os.path.join(os.getcwd(), 'mazetool') )
['__init__.py', 'person.py', 'room.py', 'maze.py', '__pycache__', 'exit.py']
You may get also
.pyc files. Those are "Compiled" temporary python files that the system generates to speed things up. They'll be regenerated
on the fly when your
.py files change. They may appear inside the
We want to
import these from notebooks elsewhere on our computer:
it would be a bad idea to keep all our Python work in one folder.
The best way to do this is to learn how to make our code into a proper module that we can install. We'll see more on that in a few lectures' time (notebook).
Alternatively, we can add a folder to the "
PYTHONPATH", where python searches for modules:
import sys print('\n'.join(sys.path[-3:]))
from pathlib import Path sys.path.append(os.path.join(Path.home(), 'devel', 'libraries', 'python'))
I've thus added a folder to the list of places searched. If you want to do this permanently, you should set the
PYTHONPATH Environment Variable,
which you can learn about in a shell course, or can read about online for your operating system.