0 points
Submitted by a_sharma10
8 years ago

# I don't understand Dot Notation

I don’t understand it at all! Will someone talk me through it please?

Sure (note that the following applies specifically to Python but is also true of many other languages). Python, like many programming languages, supports Object Oriented Programming or OOP for short. In this paradigm (type of programming), we approach ideas as Objects much as we do in the real world. Each Object is an instance of a Class or a type of object. For example, I am Michael Rochlin. I am a person. I am also a Codecademy member and also a Codecademy Moderator. So we could say that there is an object, which we will call `michael_rochlin` and it is an instance of a class `person`.

Now every `person` can say his/her name so we might have a function or method that tells the person to say his/her name. That method would be called `say_name`. It would be written inside the definition of the class `person` so that every `person` could use it.

Then we would create an instance of `person` and name it `michael_rochlin`. This instance is only one `person` and we could have other instances like `zach` or `eric` or `linda`(who are all Codecademy staff members BTW.)

So what does all this have to do with dot notation? Dot notation allows us to tell a instance of a class to use one of the methods inside that class. So if we called `michael_rochlin.say_name()` it would call the method `say_name()` that was written in the `person` class because `michael_rochlin` is a `person`.

“But Michael, we haven’t learned anything about classes or OOP or objects or anything like that. What are you talking about!??”

In Python, almost everything you use is an object. You have used at least seven different classes of Objects. You have used Integers, Floats, Strings, Lists, Tuples, Dictionaries and Booleans. (don’t worry if you haven’t, you will) These are all special classes in Python and each has it’s own methods.

One method of the `List` class is `append()` which appends a value to a list. What you are really doing is calling the method `append` from the `List` class on that object.

(There is a similar idea by modules, but its practically the same…)

Hope that helped, even if it was a little complicated. If you want more help, let me know

1703 points
Submitted by Michael Rochlin
8 years ago

a_sharma10 8 years ago

woahhh… I didn’t understand that. But thanks for your time and effort! Really appreciated!

Michael Rochlin 8 years ago

Ya like I said. I’ll write a much simpler version right now also…

corner xu 7 years ago

I like this version. This question has confused me for a long time. Thx for this excenllent answer. May I ask another question? Is there any rules about the code used in the brackets of a dot function?Like what how can I use “y” in x.upper(y)?

Simon Bhattacharya 7 years ago

@corner xu hmm, you cannot pass an argument in upper() function, say for an example if you try to run this code

x = “this is in small caps” y = “hmmm”

# now if you ttry to print x.upper(y) you will get a error saying as

TypeError: upper() takes no arguments (1 given) if that’s what you meant. @michael thanks for the brief answer, quite a bit helpful in understanding OOP

Santosh Jayanthy 7 years ago

i like Michael’s explanation…awesome…codecademy is gonna change my life…thanks

Timo J 6 years ago

This was beautiful <3

spinc 5 years ago

That is the first time I have been able to see the relationship the different ‘parts’ , thank you, really helpful analogy.

skinners82 5 years ago

This was a really helpful explanation. Thanks!

So here’s a simpler explanation. There are two kinds of functions (actually one is technically a method but we’ll ignore that). One kind of function takes an argument by putting that argument inside the parentheses. For example - `len("mystring")` will return `8` because there are 8 letters in `"mystring"`. (See footnote one for slightly more detail)

Another kind of function is one that is specific to a type or class of objects. An example of a class is List. An example of a List is `[1,2,3,4]`. The class List has functions defined that work specifically on Lists. To use those functions on a specific List we would use dot notation. For example, to use the special function `append` on a List called `my_list` we would write `my_list.append(insert_thing_to_append)`. (See footnote 2 for a little more)

Hope that is a simpler way of explaining it. You will come across dot notation by functions for Lists, Dictionaries and Strings quite often. You will also use them for user-defined classes and even for using specific functions from modules and libraries.

Footnotes:

1. `len` is an example of a function that is defined in the `__builtin__` namespace which is the environment you are working in. Almost everything in Python is actually an object and therefore part of a class or a module. So technically `len` and other such built-in global functions are part of the `__builtin__` module. Not important to know though…
2. There are many kinds of built-in classes, the most common being `List`, `String` and `Dict`. Each of these builtin classes have associated methods that are defined in the source code.
3. In general, dot notation tells Python to look inside the space that is before the dot for code to execute. You can use dot notation to access the specific version of a certain function that is defined in a different class or a different module. For example, if I have one module that is called `basicmath` and another called `advancedmath` and they both have constants `PI`, but with different values, then I would call `basicmath.PI` to get that version of PI, and `advancedmath.PI` to get its version of PI.
1703 points
Submitted by Michael Rochlin
8 years ago

Test_man 7 years ago

This is helpful (especially along with the answer from Michael), but what is the best way to get to know when to use either? Or is it rote memorization?

Timo J 6 years ago

Can this be included in the lesson? As in this explanation.

jeremyisboss 6 years ago

sup

mousewithatache 5 years ago

Lesson #9 says “Methods that use dot notation only work with strings.” But you say list can use dot notation too?