Welcome to programming! Ipython/Juptyer notebooks will be our primary tool when conducting data science. The first thing to know with this is that each cell block [of code] can be run be pressing shift+enter. Try running the (and tinkering) the below code blocks to see what returns:

print('This is code being run.')

This is code being run.

The Python language can also work as a calculator. Try running and editing the below cells and see what it returns

2 + 2

10

(2/4) +(3 * 4)
# spaces don't matter

12.5

5 + 11
44 - 8 # notice that only the last line of code returns as the output

36

print(5 + 11)
44 - 8
# notice that the printed statement and the last line returns

16





36

You might have started to notice that the code blocks have little notes that say In [ ]: before you run them, and then are filled with a number after you run them. This is important, as it tells you what order cell blocks were run. (Which can sometimes affect how your code runs.)

You may also notice that other cell blocks, such as this one, do not have the In [ ]: label as with the code blocks. This is because this cell block is formatted as Markdown rather then code. You can see (and change) what type of cell is by clicking the dropdown menu at the top:

Markdown can accept different formatting methods to display text and images in helpful ways. Doubleclick any Markdown cell in this notebook to see how it is written. Some quick tips:

• Headers are created by a # before the text. The more ##, the smaller the header
• Bullets are created with a *
• Bold words are surrounding the text with **
• Italics are made by surrounding the text with *
• Text can also be formatted as code by surounding the text with the backtick symbol, `

You can create ordered lists as well with numbers instead of *.

1. First point
2. Second point

You can create a table with | and -- between rows and columns like this:

You can also embed links in text in this format: [link text](http://url)

Here is a helpful link for other Markdown formatting techniques:

https://medium.com/ibm-data-science-experience/markdown-for-jupyter-notebooks-cheatsheet-386c05aeebed

As you expand your notebook, you can use common shortcut to create a new cell (instead of clicking the + symbol in the top left) either above or below the current cell you have selected.:

• Esc + a will create a new cell immediately above
• Esc + b will create a new cell immediately below
• Double tapping d will delete the currently selected cell

You should also start to notice that when you are in a cell writing code (or notes), the cell is highlighted in green meaning you are in edit mode.

Alternatively, if you press esc, the cursor will be in blue inidicating that you are in command mode.

Edit mode is the standard mode for editing cells, whether its writing code or notes. To enter edit mode from command mode simply hit enter, or double click on a cell.

In command mode, you can delete cells, add cells, copy cells, paste cells, change cell types, and more. You can also do these tasks in a more cumbersome (and time consuming) manner by using the various headers in the menu bar at top. You can also see a full list of shortcuts available in command and edit mode under the help menu.

We can also run bash commands just as we did before from the terminal directly within iPython notebooks!
(Note: bash commands cannot be mixed with python and must be in their own cell block.)

Try it out!

pwd

ls

You can write in plain english in a code cell but not have that line be run.

# This is a comment. This line will not run
4+7 
# The line above will run because it is not 'commented out'

11

9 - 4 # everything after the # will be commented out, but the calculation will still run

5

Note the green text following the # in the cell above.

Anything following a # in python is a comment and will not execute. This is a useful feature for annotating your code with notes for yourself and other later so that your code is easy to read.

A shortcut to comment out code is, while your cursor is in the line you want to comment out, hit Ctrl + / and it will add a # at the front of the line

In Python, we can define a object that is stored in memory. We can use that object, which represents whatever we want, in other lines of code. An object is also called a variable.

To define a variable or an object, simply use the equal sign:

variable_name = what_to_store_in_the_variable

Always have the name of the object on the left side of the equals sign. Run and tinker the cells below with different or new objects.

# let's make some objects!
a = 5
b = 9

a + b

14

print(a * b)

45

word = 'apple'
word2 = 'pear'
print(word, word2)

apple pear

You can also check what type of object something is using the built in type() method. This can be useful when determining how to work with an object that you are unfamiliar with. Basic object types are:

• int - Integer. This is a whole number
• str - String. This is a list of characters (aka text).
• float - Float. This is a non-whole number (aka a number with decimal points)

type(a)

int

type(word)

str

pi = 3.141
type(pi)

float

type(3.141)

float

We have used one built in python functions: * print() #Prints stuff! In general, python has reserved keywords for built in functions like this. Be sure to not name your variables any of these!

# let's try some of the built in functions!
len(word)
# returns the length of characters in a string object

5

list(word)
# turns a string object into a list of each character

['a', 'p', 'p', 'l', 'e']

list(range(0, 10))
# returns a list of numbers between 0 (inclusive) and 10 (exclusive)

[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

Sometimes, the code cell you have written will not run. That is because it is not written in a way the Python language requires it. See what happens when you run the code below

'apple' + 2

---------------------------------------------------------------------------

TypeError                                 Traceback (most recent call last)

<ipython-input-8-58195d5e30ca> in <module>()
----> 1 'apple' + 2


TypeError: can only concatenate str (not "int") to str

object_name

---------------------------------------------------------------------------

NameError                                 Traceback (most recent call last)

<ipython-input-43-84d944bb2bcf> in <module>()
----> 1 object_name


NameError: name 'object_name' is not defined

This is good for us! Reading and understanding errors will help you be a better coder. Always look to the last line to see the type of error we have to deal with. Then look up to see where the ----> arrow points to. This will point to the line of problematic code that should be revised.