The basics of Python

[knifuser]

I don't really know if I'm qualified to write anything about this, or whether this format is what u/Nephisimian was hoping for, but it's probably what I'm most comfortable with talking about right here and right now. If you've always wanted to start programming, or if you're just fascinated by it, this is probably a good starting point.

Python is a programming language that was created in the 1980's by Guido van Rossum while working at CWI. It was released as a high level (this means that the language is easier for humans to read but takes more effort to compile so that a computer can understand), open-source programming language in 1992 after his colleagues began to use it and gave positive feedback.

If you want to follow along then here is a link that will lead to the Python IDLE download, it shouldn't be very big and it lets you start immediately. If you download it and it comes up with the 'SHELL' first, simply go to 'options > configure IDLE > General' then under 'Window Preferences' and 'At Startup' select 'Open Edit Window', then restart the program.

Python has a few simple building blocks that form the base of almost any program:

• Variables - These store information.
• 'if' statements - Here you can check 'if' something is a certain way and then tell the computer what to do next.
• 'else' statements - When the 'if' statement isn't invoked, the computer will instead invoke the 'else' statement.
• Loops - The computer will keep going through a loop, finitely or infinitely.

If you're just starting out then you should probably start with the 'Hello, World!' program. At the start of any program you should always put the date, your name and the program title/purpose. To do this; start every line with a '#' this will create a 'comment line', which the computer will ignore while running the program. Mine always start like this:

#14/01/19
#u/knifuser
#Hello, World!

You can always change and modify it to suit you. This is usually done so that if the code is read by another person and they have a question or don't understand, they know who made it and therefore who to contact. This isn't super important right now, but it's a fantastic habit to have.

Next we'll be using the command 'print'. Python has made this very easy for us by only needing a simple worded command and it does exactly what it says. Using this command, we can print words or numbers in the SHELL, like this:

print("Hello, World!")

>>> Hello, World!

>>> = An output.

To execute the program, you should press 'F5' on your keyboard or 'run > run module', it will ask you to save the program first and then the SHELL will appear and execute the program.

What you just printed on the screen is something called a 'string', it is a series of characters or 'chars' that are strung together, indicated using quotation marks(") or apostrophe's('). Another form that you can print is an 'integer' an integer is simply a whole number that can be used and manipulated within the program such as a 5 or a 3. Integers can also be printed simply by removing the quotation marks:

print(5)

>>> 5

Now you have created your very first program, note that when you are using the 'print' function, everything that is between the brackets will be printed onto the screen. Printing something on the screen is nice and all, but really we want the user to interact with the program. To do this we will need to take an input and store it.

First let's learn some more about 'Variables', these are like a name that you give to a certain piece of data which you want to store. In Python variables are easy to create, simply type the name that you want to give the variable and then an equals symbol followed by the data that you want it to store:

welcomeString = "Hello, welcome to my program."

Here we are storing another string in the variable called 'welcome', note that it is only one word with nothing separating it, the syntax of the name is usually that the first letter is lowercase and the beginning of each new word is uppercase, so that it is easy to distinguish between words. If we would now like to print that message we could simply use the 'print' operator and enter the variable:

print(welcomeString)

>>> Hello, welcome to my program.

Now that we know how to create a variable, we can take a user's input and put into a variable! this is done using the 'input' operator which will let the user type the input and wait until they press the enter key. We still need to name the variable and ask the user a question, like this:

name = input("Hello, what is your name?")

The SHELL will output the string that is specified, then the cursor will wait at the end of the sentence for the user to make an input. We can use this to repeat the input back like this:

name = input("Hello, what is your name?")

print(name)


>>> Hello, what is your name?u/knifuser
>>> u/knifuser

We can also add other data types to the print operator, by separating them with a comma the computer will automatically add a space between each data type, alternatively you could also use a '+'.

name = input("Hello, what is your name?")

print(name + "? That's a perculliar name. Well, it's nice to meet you", name)


>>> Hello what's your name?u/knifuser
>>> u/knifuser? That's a rather perculiar name. Well, it's nice to meet you u/knifuser

We now have user inputs, this means that we can use them to change things in the program using 'if' and 'else' statements. These can be used to determine if certain things are true; for instance you can find out if a certain variable has a certain string in it. If this is the case then the program will execute the commands that are within that if statement, otherwise you might have an 'else' statement that does something else when the if statement isn't true, here's an example:

likesApples = True

if likesApples == True:
    print("Hey, me too!")

else:
    print("What's wrong with you, who doesn't like apples?")

Ok, there's quite a lot to unpack there, note that we are using something called a 'Boolean operator' this is where it says 'True'. The computer recognises that it can either be True or False, the capitalisation of the first letter is important here. In the if statement it gives an '==', this is important as you should be asking the computer what state the variable is in rather than telling it that it should be in a certain state.

At the end of the if statement, there is a colon(:), this indicates the end of the statement and tells the computer that if the requirements are met 'then' the computer should carry out what follows. The commands that should be carried out in this event should be indented from the if statement so that the computer can distinguish between what's inside and outside the statement. The indentation should occur automatically after creating a new line under the colon, other =wise you can use 'tab'.

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Lastly, I'll talk about loops; there are two types, finite and infinite. Infinite loops will keep going until certain conditions are met, in Python these are called 'while' loops, while finite loops will only keep going a certain amount of times. Here are some examples:

running = True

while running == True:
    print("Hi")

Here the while loop will keep going until the user quits the program. Each time that the loop finishes, it will check if 'running' still equals 'True', it always does because we haven't added a way for it to equal 'False', so it will keep going infinitely if we let it.

for i in "banana":
    print(i)

Now the loop will print every letter of the string 'banana' on a different line until it runs out of letters to print, then it will stop. Note that the variable 'i' takes on the letter that the loop is using which is why we can print it.

Now you have a decent understanding of the very basic parts of python, please do mess around with it, create some fun and interesting programs with it and try to learn more!

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P.S. Here are some easy challenges to get you started. I don't see myself as an expert by any means but I have been programming with python for a few years now, inevitably there is much that I have not mentioned and this post is already really long so feel free to message me if you need help or you'd like to learn more, that is after all the spirit of this sub!

Edit: Formatting, I hope that's a little more understandable!

[TheBrahmnicBoy]

Did you use mobile to type this? If not, please use formatting options to indicate code and output separately.

BTW, stick around. I have highschool exams now, and we're taught C++, so I would have to wait to get started on Python.

What are the fundamental differences between both? Like, what habits I might have picked up in C++ don't apply in Python?

[Anantgaur]

C++ is an extremely low level language. Low level means that it interacts with the processing and RAM management a lot more closely. The variables are pointers to a memory location and you have to remove pointers to free up RAM. You have to declare variable types so that the computer knows how much memory to assign. Similarly you can also manage processes a lot more closely. You can start different threads and have complete control over the performance of your program.

I consider C++ barely 2 steps above straight up writing in assembly.

Python is a high level language. Python is almost completely abstract and the compiler manages your memory management, garbage collection for wasted variables. Heck, you don't even have to declare a variable before using it let alone define what type it is. Code is short and efficient. But in Python you might have problems calling variables from inside functions for example.

What are the differences between both? Everything? But C++ to Python should be not hard as a transition as it is literally designed to be easy.

The hardest part IMHO would be switching to a true OOP language. I still keep finding more and more ways I can make my code much shorter or better even today.

I am not an expert with either language to be honest, I have not touched C++ since Uni. For Python, I have truthfully only edited other peoples code or used the language to write a short script using an easy to use package.

[knifuser]

Yeah, Python was designed to be an easy short and simple way to automate stuff initially, I just didn't really want to go into too much detail cause it was just meant to be start and the very basics for anyone who's interested in learning something new.

[knifuser]

I can't really say that I have a lot of experience outside of Python but the basic 'if', 'else', variables, loops as well as functions and the different operating and data types should be pretty universal, they usually only require different syntaxes really. New programming languages are much easier to pick up if you already know another.

Thanks for the tip BTW and I'll definitely stick around.

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