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Intro to Python pt. 1

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Intro to Python pt 1

Lesson Objectives

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Create a variable and assign it a value
Explain the different data types
Perform calculations with variables
Use string operations
Create a list
Access an element of a list
Use conditional statements to perfom a set of commands depending on the situation

Set up

In today's student_examples directory, touch a file program.py

Running files

These notes are for python 3.x, so use python3 <YOUR FILENAME>.py to run your files

Print a message

You can print a message to the user

print("hello!")

Add a comment

Comments let you summarize what you're doing
They don't get executed

# this will not be executed

Python doesn't have a specific syntax for multi-line comments so we just use a # for each line.

# to do multiple line comments
# you have to put a hash at the start of every
# line

Create a variable and assign it a value

a = "hello"
print(a) ##print the value of the variable 'a'

Data Types in Python

There are lots of different types of data that you can use in python

String (text)
Integers (whole numbers)
Float (decimal numbers)
Booleans (True/False)

You can convert one data type to another

a = str(1) #a = "1"
b = int("5") #b = 5
c = float(4) #c = 4.0
d = int(5.7) #d = 5

Performing Calculations

a = 1
b = a + 1 #b = 2
c = b * 3 #c = 6
d = c - 1 #d = 5
e = d / 2 #e = 2.5
f = d ** 2 #exponent: f = 25

String Operations

a = "first string"
b = "second string"
c = a + " " + b

Lists

You can create lists of things

a = [1, 5, "some string", True, 5.6]

You can even have lists of lists

a = [
    [1, 2, 3], #first row
    [4, 5, 6], #second row
    [7, 8, 9], #third row
    [10] #fourth row
]

You can conceptualize a list of lists however you want

ACTIVITY

If you want to make the previous example have columns instead of rows, do you need to change anything?

Access an element of a list

Lists have elements stored at numerical indexes, starting at 0

a = [1, 5, "some string", True, 5.6]
print(a[0]) #1
print(a[1]) #5
print(a[4]) #5.6

Dictionaries

You can create JS style objects in python called dictionaries

Dictionaries use array access syntax:

my_car = {
  "brand": "Ford",
  "model": "Mustang",
  "year": 1964
}
print(my_car["brand"])

You can also have lists in dictionaries and dictionaries in lists!

a = [
    {
    "brand": "Ford",
    "model": "Mustang",
    "year": 1964
    },
    [4, 5, 6],
    [7, 8, 9],
    [10]
]
print(a)

b = {
  "firstGrade": ["Bobby", "Kyle", "Suzy"],
  "secondGrade": ["Jennifer", "Jasmine", "Javier"],
  "thirdGrade": "Nobody, they all failed last year!"
}
print(b)

Perform a set of commands depending on a situation

a = 22
if a < 10:
    print("a is less than 10")
elif a == 10:
    print("a is 10")
else:
    print("a is greater than 10")

The conditions can be

< less than
> greater than
<= less than or equal to
>= greater than or equal to
== an exact match
!= not equal to

You can also compare strings:

a = 'oh hai!'
if a == 'oh hai!':
    print('this works')

You can combine conditional statements:

check to see if both conditions are met:

a = 1
b = 2
if a == 1 and b == 2:
  print('y') # will print only when both a==1 AND b==2
else:
  print('n') # will print if either condition is false

if a == 0 and b == 2:
  print('y') # will print only when both a==1 AND b==2
else:
  print('n') # will print if either condition is false

check to see if either condition is met:

a = 2
b = 2
if a == 1 or b == 2:
  print('y') # will print when either a==1 OR b==2
else:
  print('n') # will print if both conditions are false

if a == 1 or b == 1:
  print('y') # will print when either a==1 OR b==2
else:
  print('n') # will print if both conditions are false

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