Classes and Objects in Python
The most important starting point is this: in Python, everything used in a program is generically called an object.
One Idea Behind Many Values
When you work with a number, a string, or a function in Python, you are working with something Python generically calls an object. This gives Python one broad way to describe the values used in a program. Instead of treating simple values as completely separate from more complex values, Python treats them all as objects.
The most important starting point is this: in Python, everything used in a program is generically called an object.
Names and Objects
A variable is a name or reference that points to an object in memory. The variable does not contain the object itself. This distinction matters because the name and the object play different roles: the name gives your program a way to refer to something, while the object is the value being referred to.
Generated example: imagine a label attached to a storage container. The label is not the contents of the container, but it gives you a way to identify those contents. In the same way, a variable name is not the object itself; it refers to the object.
Kinds of Python Objects
Python's object model includes values that beginners often think of as unrelated categories. Numbers are objects. Strings are objects. Functions are objects. Other values used in a program are also objects. The point is not that these values all behave identically; the point is that Python uses the general concept of an object for all of them.
| Value category | How Python describes it |
|---|---|
| Number | An object |
| String | An object |
| Function | An object |
| Other value used in a program | An object |
Python applies the general term object to numbers, strings, functions, and more.
Following a Reference
Two Names, One Object
Generated example: suppose one variable name refers to a number object, and a second variable name is made to refer to that same object. What should you keep separate in your mental model?
- 1Identify the names
There are two variable names. Each name is a reference used by the program.
- 2Identify the object
The number is the object. It is not the same thing as either variable name.
- 3Follow both references
Both names can refer to the same object. The names remain separate references, while the object they refer to is shared.
- 4Keep the roles distinct
Do not describe the variable as containing the number. Describe the variable as referring to the number object.
A variable is a name or reference, and an object is the value to which that reference points. Multiple variable names can refer to the same object.
What do you think happens?
If two variable names refer to the same object, are the variable names and the object identical?
Reveal answer
No. The names are references, while the object is the value being referred to.
Python distinguishes a variable name from the object in memory that the name refers to. Two names may refer to one object without becoming that object.
Objects Have Three Aspects
Python is strongly object-oriented. This means that all values, including simple values such as integers, are objects with type, identity, and value.
- Type: an aspect of every Python value because every value is an object.
- Identity: an aspect of every Python value because every value is an object.
- Value: the information represented by the object.
For this lesson, the practical consequence is more important than memorizing terminology: even a simple integer belongs to Python's object model. A variable gives your program a reference to that object, rather than serving as a container that literally contains the object.
What This Lesson Establishes About Classes
The supplied material establishes the object side of the topic: Python treats everything used in a program as an object, and variables refer to objects. It does not provide a definition of a class, instructions for creating a class, or a detailed account of how classes produce objects. Therefore, use this lesson as the foundation for understanding objects and references before studying the additional mechanics of classes.
Do not let the word class distract from the central relationship established here: a variable name refers to an object, and Python uses the object concept for numbers, strings, functions, and more.
Mistakes with Names and Values
Common mistake Treating a variable as if it contains the object itself.
What it looks likeDescribing a variable name as the number rather than as a reference to a number object.
Why it failsThe source distinction is that a variable is a name or reference, while the object is the value in memory.
Do this insteadSay that the variable refers to the object.
Common mistake Assuming that only complex values are objects.
What it looks likeThinking that a function can be an object but an integer cannot.
Why it failsPython's object-oriented model includes all values, including simple values such as integers.
Do this insteadRemember that numbers, strings, functions, and other values are all objects.
Common mistake Confusing two variable names with two objects.
What it looks likeAssuming that two names must identify two separate objects.
Why it failsMore than one variable name can refer to the same object.
Do this insteadTrace each name to the object it refers to instead of counting names as objects.
Check Your Mental Model
For each statement, decide whether it correctly describes Python's object model. Then rewrite any incorrect statement.
- A variable is the object stored in memory.
- A string is an object in Python.
- A function is an object in Python.
- Two variable names can refer to the same object.
- An integer is excluded from Python's object model because it is a simple value.
Hints
- Separate the name or reference from the object it refers to.
- The object concept includes numbers, strings, functions, and more.
- Simple values such as integers are included.
- 1A strong answer identifies statements 1 and 5 as incorrect. A variable is a name or reference, not the object itself. An integer is an object, even though it is a simple value. Statements 2, 3, and 4 match the object-and-reference model.
Key Takeaways
- Python generically calls everything used in a program an object.
- Numbers, strings, functions, and other values are all objects.
- A variable is a name or reference that points to an object in memory.
- The variable does not contain the object itself.
- Python's strongly object-oriented model gives values a type, identity, and value, supporting flexible and consistent code.
At a glance
- Everything used in a Python program is generically called an object.
- Numbers, strings, functions, and simple values such as integers all belong to the object model.
- A variable is a name or reference, not the object itself.
- A variable refers to an object in memory, and multiple names can refer to the same object.
- Understanding objects and references is a foundation for writing flexible, consistent Python code.