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GeezerVison is showing github.com — Edits · IHackPy/practical-python@cc15724

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  • Notes
    • 01_Introduction
      • 02_Hello_world.md
      • 06_Files.md
    • 02_Working_with_data
      • 07_Objects.md
    • 04_Classes_objects
      • 01_Class.md
      • 02_Inheritance.md
      • 03_Special_methods.md
      • 04_Defining_exceptions.md
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‎Notes/01_Introduction/02_Hello_world.md‎

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@@ -291,24 +291,19 @@ The `if` statement is used to execute a conditional:
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```python
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if a > b:
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# a is greater than b
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print('Computer says no')
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else:
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# a is lower or equal to b
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print('Computer says yes')
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```
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You can check for multiple conditions by adding extra checks using `elif`.
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```python
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if a > b:
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# a is greater than b
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print('Computer says no')
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elif a == b:
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# a is equal to b
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print('Computer says yes')
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else:
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# a is lower to b
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print('Computer says maybe')
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```
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‎Notes/01_Introduction/06_Files.md‎

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@@ -66,7 +66,7 @@ with open(filename, 'rt') as file:
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# Process the line
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```
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### Common Idioms for Write to a File
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### Common Idioms for Writing to a File
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Write string data.
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‎Notes/02_Working_with_data/07_Objects.md‎

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@@ -139,7 +139,7 @@ True
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>>>
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```
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For example, the inner list `[100, 101]` is being shared.
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For example, the inner list `[100, 101, 102]` is being shared.
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This is known as a shallow copy. Here is a picture.
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![Shallow copy](shallow.png)
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‎Notes/04_Classes_objects/01_Class.md‎

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[Contents](../Contents) \| [Previous (3.6 Design discussion)](../03_Program_organization/06_Design_discussion) \| [Next (4.2 Inheritance)](02_Inheritance)
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13
# 4.1 Classes
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This section introduces the class statement and the idea of creating new objects.
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### Object Oriented (OO) programming
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A Programming technique where code is organized as a collection of *objects*.
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A Programming technique where code is organized as a collection of
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*objects*.
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An *object* consists of:
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* Data. Attributes
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* Behavior. Methods, functions applied to the object.
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* Behavior. Methods which are functions applied to the object.
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You have already been using some OO during this course.
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For example with Lists.
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For example, manipulating a list.
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```python
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>>> nums = [1, 2, 3]
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`nums` is an *instance* of a list.
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Methods (`append` and `insert`) are attached to the instance (`nums`).
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Methods (`append()` and `insert()`) are attached to the instance (`nums`).
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### The `class` statement
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Use the `class` statement to define a new object.
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```python
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class Player(object):
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class Player:
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def __init__(self, x, y):
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self.x = x
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self.y = y
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>>>
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```
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`a` anb `b` are instances of `Player`.
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`a` and `b` are instances of `Player`.
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*Emphasize: The class statement is just the definition (it does nothing by itself). Similar to a function definition.*
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*Emphasize: The class statement is just the definition (it does
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nothing by itself). Similar to a function definition.*
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### Instance Data
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This data is initialized by the `__init__()`.
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```python
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class Player(object):
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class Player:
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def __init__(self, x, y):
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# Any value stored on `self` is instance data
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self.x = x
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Instance methods are functions applied to instances of an object.
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```python
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class Player(object):
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class Player:
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...
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# `move` is a method
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def move(self, dx, dy):
@@ -113,15 +119,15 @@ def move(self, dx, dy):
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By convention, the instance is called `self`. However, the actual name
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used is unimportant. The object is always passed as the first
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argument. It is simply Python programming style to call this argument
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argument. It is merely Python programming style to call this argument
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`self`.
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### Class Scoping
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Classes do not define a scope.
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Classes do not define a scope of names.
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```python
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class Player(object):
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class Player:
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...
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def move(self, dx, dy):
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self.x += dx
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self.move(-amt, 0) # YES. Calls method `move` from above.
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```
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If you want to operate on an instance, you always have to refer too it explicitly (e.g., `self`).
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If you want to operate on an instance, you always refer to it explicitly (e.g., `self`).
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## Exercises
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Note: For this exercise you want to have fully working code from earlier
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exercises. If things are broken look at the solution code for Exercise 3.18.
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You can find this code in the `Solutions/3_18` directory.
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Starting with this set of exercises, we start to make a series of
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changes to existing code from previous sctions. It is critical that
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you have a working version of Exercise 3.18 to start. If you don't
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have that, please work from the solution code found in the
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`Solutions/3_18` directory. It's fine to copy it.
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### Exercise 4.1: Objects as Data Structures
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One thing to emphasize here is that the class `Stock` acts like a
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factory for creating instances of objects. Basically, you call
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it as a function and it creates a new object for you. Also, it needs
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to be emphasized that each object is distinct---they each have their
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it as a function and it creates a new object for you. Also, it must
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be emphasized that each object is distinct---they each have their
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own data that is separate from other objects that have been created.
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An object defined by a class is somewhat similar to a dictionary--just
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### Exercise 4.3: Creating a list of instances
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Try these steps to make a list of Stock instances and compute the total
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cost:
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Try these steps to make a list of Stock instances from a list of
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dictionaries. Then compute the total cost:
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```python
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>>> import fileparse
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### Exercise 4.4: Using your class
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Modify the `read_portfolio()` function in the `report.py` program so that it
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reads a portfolio into a list of `Stock` instances. Once you have done that,
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fix all of the code in `report.py` and `pcost.py` so that it works with
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`Stock` instances instead of dictionaries.
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Modify the `read_portfolio()` function in the `report.py` program so
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that it reads a portfolio into a list of `Stock` instances as just
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shown in Exercise 4.3. Once you have done that, fix all of the code
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in `report.py` and `pcost.py` so that it works with `Stock` instances
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instead of dictionaries.
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Hint: You should not have to make major changes to the code. You will mainly
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be changing dictionary access such as `s['shares']` into `s.shares`.

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