2.1. 10min - Python Starter Kit

This starter kit was meant for readers that have never used python and have very little knowledge of programming concepts.

2.1.1. Installation - Windows Guide Only

  1. Download the latest version of python from python.org

  2. During installation all the default selection will work, but pay attention to where python is being installed. The newer versions on windows will be placed under: c/users/yourusername/AppData/Local/Programs

  3. Once python is installed browse to folder it was installed in, something like c/users/yourusername/AppData/Local/Programs/Python38-32 and inside you will see a python.exe

  4. Add the python folder to your windows PATH so that you can pull up python from any terminal (cmd, powershell, bash).

    4.1) Hit the windows start menu (bottom left windows icon)

    4.2) Type environment and you are looking for edit environment variables for your account

    4.3) Highlight Path and hit edit

    4.4) A new window will open, hit new and paste in your path where python was installed c/users/yourusername/AppData/Local/Programs/Python38-32

    4.5) Hit OK on both windows and you are good to go!

  5. Running python: pull up a terminal (start menu > cmd > enter) and type python. If the terminal hangs on windows try python -i where -i is interactive, or winpty python

Things you should know about:

  • Python is manually downloaded from python.org. There is no update button to get a newer version, you will have to go back to python.org and download a new version manually again.

  • When installing Python, you are also installing a python package installer (pip) that unlocks python’s superpowers. Packages can be imported with a single line of a code and before you know it you are scraping the web, working on excel/text files or performing machine learning with only 10 lines of code.

  • Everything in python is about versions. Python has a version, under it your pip has a version, under that your packages will have versions.

2.1.2. Run your first Script

You have python installed and it works. Now you can type away at a python session in a terminal but once you close the terminal, your code will also be gone. So instead we can write a script can you can call any number of times:

  1. create a script file (lets say on your desktop): Right Mouse Button > New > Text Document

  2. rename it myscript.py

  3. open it with your text editor (notepad++ is a decent pick)

  4. type out your python code and save, example:

print("Hello World!")

  1. run your script by typing python myscript.py in your terminal(your terminal has to be in the same folder). Start Menu > type “cmd” > enter > then in the terminal cd Desktop then try python myscript.py

2.1.3. Python Highlevel Concepts

Note

“>>>” is not part of any code, it is simply shown here to distinguish between code written and its output results. (ie. do not copy/write lines containing “>>>”)

Note

the following names are reserved for python internals, and should not be used as variable names false none true and as assert break class continue def del elif else except finally for from global if import in is lambda nonlocal not or pass raise return try while with yield

2.1.3.1. Basics

  • code comment: # this is a comment

  • define a variable (no declaration needed!): a = 5

  • understand your basic types:

    • int:1 or 2342134

    • float: 1.0 or 2342134.12341234

    • string: "this" or 'that' both valid but double quotes is better for "it's a nice day"

    • list (arrays if you prefer): 1D [1,2,3] 2D [[1,2,3],[10,20,30],[100,200,300]]

    • there are a lot more but these are the basics

2.1.3.2. What can I do with integers/floats (math)

a = 5
b = 10
c = a + b
print(c)
>>> 15
# add, subtract, multiply, divide, power
5 + 10 - 10 * 5 /5 ** 2
>>> 13.0

2.1.3.3. What can I do with strings

  • split up text

a = 'this is a string'
b = a.split(" ") # split text base on " " single spaces
b
>>> ['this', 'is', 'a', 'string']

  • replace characters

a = 'this is a string'
b = a.replace('s','S')
b
>>> 'thiS iS a String'

  • add two strings

a = 'this'
b = 'that'
c = a + b
c
>>> "thisthat'
# or use join, note items have to be in square brackets
d = ' '.join([a,b]) # join "a" and "b" with a " " space
>>> 'this that'

  • sub-strings (slicing)

../_images/list_slicing.png

List slicing

a = 'this is a string'
a[0] # index to a character (python indexing start at 0)
>>> 't'
b = a[0:4] # give me the characters from index 0 to start-of index 4, t=0,h=1,i=2=s=3,4=' '
b
>>> 'this'

2.1.3.4. What can I do with lists

  • indexing

a = [10,20,30]
a[0] # python indexing starts at 0
>>> 10
a[0:2] # from index 0=10, to right before index 2=30 so that's 20
>>> [10,20]

  • add to a list

a = [] # empty list
a.append(10) # append one at a time
a += [20,30] # add another list to it
a
>>> [10,20,30]

  • 2D array (really just a nested list)

x = [10,20,30] # 3 x-coordinates
y = [40,50,60] # 3 y-coordinates
myarray = list(zip(x,y))
myarray
>>> [(10, 40), (20, 50), (30, 60)]
myarray[1] # what is the x,y -coordinate of point 2 (note again python index starts from 0)
>>> (20,50)
myarray[1][0] # what is the x-coordinate of point 2
>>> 20
myarray[1][1] # what is the y-coordinate of point 2
>>> 50

2.1.3.5. How to write logic loops (if, for, while)

equal: ==, not equal: !=, and: and, or: or

  • if statements

if 1 == 1 and 1 == 2:
    print('1 is equal to 1 and also equal to 2')
elif 1 != 1:
    print('1 is not equal to 1')
else:
    print('none of the conditions were true')

  • for loop

mylist = [10,20,30]
for item in mylist:
    print(item)
>>> 10
>>> 20
>>> 30

  • while loop

i = 0
while i < 3:
    print(i)
    i += 1
>>> 0
>>> 1
>>> 2

2.1.3.6. How to write functions

# define function with 2 inputs
def myfunc(input1, input2):
    result = intput1 + input2 + 10
    return result

# call a function with inputs 1,2
func(1,2)
>>> 13

2.1.3.7. How do I read/write files

  • read a file

# container for lines of text out of our file
lines = []

# use the python builtin function "open" to start streaming a file for read "r"
with open('test.txt', 'r') as f:
    while True:
        # read each line in a file
        line = f.readline()
        # add each line to our container
        lines.append(line)
        # at the end of the file, line=""
        # in which case we stop reading the file and break out of the loop
        if not line:
            break

  • write a file

# writing is very similar, except we "w" for write
with open('test2.txt', 'w') as f:
    f.write('Hello World')