Finished Chapter 9

chap9_classes.md

@@ -201,7 +201,153 @@ class ElectricCar(Car):
 
 ### Instance as Attributes
 
-Sometimes we can use an instance of an class (object) as an attribute of another class.
+Sometimes we can use an instance of an class (i.e. an object) as an attribute of another class.
 
 e.g. After grouping multiple all battery related attributes/method into a new class
 
+```python
+class ElectricCar(Car):
+    """Represent aspects of a car, specific to electric vehicles."""
+
+    def __init__(self, make, model, year):
+        """
+        Initialize attributes of the parent class.
+        Then initialize attributes specific to an electric car.
+        """
+        super().__init__(make, model, year)
+        self.battery = Battery()
+    ...
+
+class Battery:
+    """A simple attempt to model a battery for an electric car"""
+
+    def __init__(self, battery_size=75):
+        """initialize the battery's attributes"""
+        self.battery_size = battery_size
+
+    def describe_battery(self):
+        """Print a statement describing the battery size"""
+        print(f"This car has {self.battery_size}-kWh battery.")
+
+    def get_range(self):
+        """Print a statement about the range this battery provides"""
+        if self.battery_size == 75:
+            range = 260
+        elif self.battery_size == 100:
+            range = 315
+        
+        print(f"This car can go about {range} miles on a full charge.")
+```
+
+Calling these functions are also simple
+
+```python
+print(my_tesla.get_descriptive_name())
+print(my_tesla.battery.describe_battery())
+print(my_tesla.battery.get_range())
+```
+
+### Modeling Real-World Objects
+
+Question: `get_range()` is this property of battery or car? Need think on higher-level.
+
+ANS: No right or wrong approach. Sometimes it's more efficient, sometimes not.
+
+## Importing Classes
+
+Python lets you store classes in modules and then import the classes you need into your main program.
+
+### Importing a Single Class
+
+e.g. 
+
+1. after separating `Car` class into a python script `car.py` (i.e. **modules**)
+2. New python script can reuse class
+
+```python
+from car import Car
+my_new_car = Car('audi', 'a4', 2019)
+print(my_new_car.get_descriptive_name())
+```
+
+### Storing Multiple Classes in a Module
+
+A module (.py script) can stores as many classes as it can. Although these classes should be related.
+
+e.g. 
+
+1. add `ElectricCar(Car)` & `Battery` into `car.py` module script
+2. New python script can reuse these classes
+
+```python
+from car import ElectricCar
+
+my_tesla = ElectricCar('tesla', 'model s', 2019) 
+
+print(my_tesla.get_descriptive_name())
+my_tesla.battery.describe_battery()
+my_tesla.battery.get_range()
+```
+
+### Importing Multiple Classes from a Module
+
+```python
+from car import Car, ElectricCar
+
+my_beetle = Car('volkswagen', 'beetle', 2019)
+print(my_beetle.get_descriptive_name())
+```
+
+### Importing an Entire Module
+
+```python
+import car
+
+my_beetle = car.Car('volkswagen', 'beetle', 2019)
+```
+
+### Importing All Classes from a Module
+
+```python
+from module_name import *
+```
+
+### Importing a Module into a Module
+
+```python
+from car import Car
+
+...
+```
+
+### Using Aliases
+
+Using Aliases can make coding easier (less wordy)
+
+```python
+from electric_car import ElectricCar as EC
+```
+
+### Finding Your Own Workflow
+
+* Keep project simple/flat
+* When start out, keep code structure simple.
+  * Try doing everything in one file and moving classes to separate modules once everything is working.
+
+## Python Standard Library
+
+Python has modules in python std library for use. Use them just like normal customized library
+
+```python
+from random import randint
+randint(1,6)
+```
+
+## Styling Classes
+
+Following PEP-8:
+
+* Class names should be written in *CamelCase*
+* Every class should have a docstring immediately following the class definition.
+* Use blank lines to organize code, but don't over-use them.
+* Sequence of importing modules: Python Standard Library + blanklines + customized modules

src/car.py

@@ -35,16 +35,32 @@ class ElectricCar(Car):
         Then initialize attributes specific to an electric car.
         """
         super().__init__(make, model, year)
-        self.battery_size = 75
+        self.battery = Battery()
-
-    def describe_battery(self):
-        """Print a statement describing the battery size."""
-        print(f"This car has a {self.battery_size}-kWh battery.")
 
     def fill_gas_tank(self):
         """Electric cars don't have gas tanks"""
         print("This car doesn't need gas tank!")
 
+class Battery:
+    """A simple attempt to model a battery for an electric car"""
+
+    def __init__(self, battery_size=75):
+        """initialize the battery's attributes"""
+        self.battery_size = battery_size
+
+    def describe_battery(self):
+        """Print a statement describing the battery size"""
+        print(f"This car has {self.battery_size}-kWh battery.")
+
+    def get_range(self):
+        """Print a statement about the range this battery provides"""
+        if self.battery_size == 75:
+            range = 260
+        elif self.battery_size == 100:
+            range = 315
+        
+        print(f"This car can go about {range} miles on a full charge.")
+
 my_new_car = Car('audi', 'a4', 2019)
 print(my_new_car.get_descriptive_name())
 my_new_car.update_odometer(23)
@@ -52,3 +68,5 @@ my_new_car.read_odometer()
 
 my_tesla = ElectricCar('telsa', 'model s', 2019)
 print(my_tesla.get_descriptive_name())
+print(my_tesla.battery.describe_battery())
+print(my_tesla.battery.get_range())