PYTHON SOCIAL MEDIA ARTIFICIAL INTELLIGENCE

Install Python environment, know how to enter expressions in Python and how to save, run, and open files! To work with plots, you will need these Python library packages: matplotlib and numpy. If you’re using Anaconda Python, your system should already have numpy and matplotlib installed. Addition (+), subtraction (-), multiplication (*), division (/), modulo (%) and power (**) operators are built into the Python language.

Below are two examples of square root calculation:

In [1]: 16**0.5

Out [1]: 4.0

In [2]: import math

In [3]: math.sqrt(16)

Out[3]: 4.0

The math module allows you to do a number of useful operations:

In [1]: math.log(16, 2)

Out [1]: 4.0

In [2]: math.cos( 0 )

Out [2]: 1.0

• try out code in your Python development environment (Anaconda, Canopy, IDLE, or whatever)
• read the Python documentation or other Python tutorials
• use a paper and pencil to sketch out solutions
• if you have the textbook, read the relevant sections
• post to the forums (or any of our social media platforms)

Programming.

We also teach computational methods.

Documentation

• Official Python 3 Documentation – “official”/technical explanation of what a particular function/operator does, examples of correct syntax, what the various libraries are, etc.
• Built in functions: https://docs.python.org/3/library/functions.html#built-in-funcs

Textbooks/Tutorials

• Dive Into Python – another survey of Python syntax, datatypes, etc.
• Think Python by Allen Downey – a good general overview of the Python language. Includes exercises.
• The Official Python Tutorial – self-explanatory
• Learn Python the Hard Way – (note: for Python 2) another free online text
• Reserved Keywords in Python – don’t use these as variable names
• PEP 8 – Style Guide for Python Code – learn what is good and bad style in Python
• CheckIO – learn Python by exploring a game world
• Invent with Python – develop your Python skills by making games or hacking ciphers
• Codecademy – (note: for Python 2) learn Python by building web apps and manipulating data; interactive tutorial sequence
• Python Tutor – interactive tutorial sequence of exercises
• Blog with tutorials – created by one of our community TAs

Debugging

• Python Tutor – an excellent way to actually visualize how the interpreter actually reads and executes your code
• DiffChecker – compares two sets of text and shows you which lines are different
• Debugging in Python – steps you can take to try to debug your program

Software

• Python Tools for Visual Studio – Visual Studio plug-in enabling Python programming

Other Q&A

• Stack Overflow – a large Q&A forum for programming concepts (not just Python). Try searching here before you post on the edX forum, and you may find that someone has already answered your question.

More practice problems

• Python Challenge – a series of puzzles you can try to test your Python abilities
• Project Euler – additional programming challenges you can try once your Python knowledge becomes stronger; problems are sorted by increasing difficulty
• Coding Bat – problems you can solve within an online interpreter
• Codewars – improve your skills by training on real code challenges

Variables

In [2]: type (3.0)

Out [2]: float

Type Conversions (Cast)

• Can convert object of one type to another
• float (3) converts integer 3 to float 3.0
• int (3.9) truncates float 3.0 to integer 3

Printint to Console

• To show output from code to a user, use print command

In [11]: 3+2

Out [11]: 5

In [12]: print (3+2)

5

Expressions

• Combine objects and operators to form expressions
• an expression has a value, which has a type
• syntax for a simple expression <object> <operator> <object>

Operators ON ints and floats

• i + j -> the sum (if both are ints, result is int. if either or both are floats, result is float.)
• i – j -> the difference (if both are ints, result is int. if either or both are floats, result is float.)
• i * j -> the product -> (if both are ints, result is int. if either or both are floats, result is float.)
• i / j -> division (result is float.)
• i//j -> int division -> result is int, quotient without remainder
• i%j -> the remainder when i is divided by j
• i**j -> i ot the power of j

Simple Operations

• Parentheses used to tell Python to do these operations first
  • 3*5+1 evalutates to 16
  • 3*(5+1) evaluates to 18
• Operator precedence without parentheses
  • **
  • *
  • /
  • + and – executed left to right, as appear in expression

Answers

• 3.14 – float
• -34 int
• True bool
• None nonetype
• 3.0 float

Binding Variables and Values

• Equal isng is an assignment of a value to a variable name
• pi – 3.14159
• pi_approx = 22/7
• Value stored in computer memory
• An assignment binds name to value
• Retrieve value associated with name or variable by invoking the name, by typing pi

Abstracting Expressions

• Why give names to values of expressions?
• Reuse names instead of values
• Easier to change code later
• pi = 3.14159
• radius = 2.2
• area = pi * (radius **2)

Programming vs math

• In programming, you do not “solve for x”
• pi = 3.14159
• radius = 2.2
• # area of circle
• area = pi * (radius **2)
• redius = radius + 1

Changing Bindings

• Can re-bind names using new assignment statements
• previous value may still stored in memory but lost the handle for it
• value for area does not change until you tell the computer to do the calculation gain
• pi = 3.14
• readius = 2.2
• area = pi * (radius **2)
• radius = radius + 1

Comparison operators on int and float

• i and j are any variable names
• i > j
• i >=j
• i<j
• i<j
• i==j -> equality test, True if i equals j
• i!=j -> inequality test, True if i not equal to j

Logic operators on bools

• a and b are any variable names
• not a -> True if a is False
  • False if a is True
• a and b -> Ture if bot are True
• a or b -> True if either or both are True

Branching programs

• The simplest branching statement is a condiditonal
  • A test (expression that evalutes to True or False)
  • A block of code to executte if the test is True
  • An optional block of code to execute if the test is False

A simple example

x = int (input )’Enter an integer: ‘))

if x%2 ==0:

print (”)

print (‘Even’)

else:

print (”)

print (‘Odd’)

print (‘Done with conditional’)

Some Observations

• The expression x%2 == 0 evaluates to True when the remainder of x divided by 2 is 0
• Note that == is used for comparison, since = is reserved for assignment
• The identation is important – each indented set of expressions denotes a block of instructions
  • For example, if the last statement were indented, it would be executed as part of the else block of code
• Note how this identation provides a visual structure that reflects the semantic structure of the program

Nested Conditionals

if x%2 == 0:

if x%3 ==0:

else:

print (‘Divisible by 2 and not by 3’)

elif x%3 == 0:

print  (‘Divisible by 3 and not by 2’)

Compound Booleans

if x < y and x < z:

print (‘x is least’)

elif y < z:

print (‘y is least’)

else:

print (/z is least’)

Control flow – branching

if <condition>

<expression>

• <condition> has a vaue True or False
• evaluate expressions in that block if <condition> is True

Indentation

• matters in Python
• how you denote blocks of code
• x = float (input (”Enter a number for x: “))
• y = float (input (”Enter a number for y: “))
• if x == y:
  • print (”x and y are equal”)
  • if y ! = 0:
    • print (“therefore, x / y is “, x/y)
• elif x < y:
  • print (“x is smaller”)
• else:
  • print (“y is smaller”)
• print (“thanks!”)

=vs==

x = float (input (“Enter a number for x: “))

y = float (input (“Enter a number for y: “))

if x == y:

print (“x and y are equal”)

if y ! = 0:

print )”therefore, x /y is”, x/y)

elif x < y:

print (“x is amller”)

else:

print (“y is smaller”)

print (“thanks!”)

What have we added?

• Branhing programs allow us to make choices and do different things
• But still the case that at most, each statement gets executed once
• So maximum time to run the program depends only on the length of the program
• These programs run in constant time

Strings, Branching, Iteration

Variables

• name
  • Descriptive
  • meaningful
  • helps you re-read code
  • cannot be keywords
• value
  • information stored
  • can be updated

Variable binding with =

• Compute the right hand side -> VALUE
• store it (aka bind it) in the left hand side -> VARIABLE
• left hand side will be replaced with new value
• = is called assignment
• x = 2
• x = x*x
• y = x+1

Binding Example

• swap variables
• – is this ok?
• x = 1
• y = 2
• y = x
• x = y
• swap variables
• x = 1
• y = 2
• temp = y
• y = x
• x = temp

Types

• Variables and expressions
  • int
  • float
  • bool
  • string — NEW
  • …..and others we will see later

STRINGS

• letters, special charactrs, spaces, digits
• enclose in quotation marks or single quotes
  • hi = “hello there”
  • greetings = ‘hello’
• concatenate strings
  • name = “eric”
  • greet = hi + name
  • greeting = hi +” ” + name

OPERATIONS ON STRINGS

• ‘AB’ + ‘CD’ -> Concatenation
• 3* ‘eric’ -> successive concatenation
• len (‘eric’) -> the length
• ‘eric’ [1] -> indexing
• ‘eric’ [1:3] -> slicing

INPUT/OUTPUT: print

• used to output stuff to console
• keyword is print
• x = 1
• print (x)
• x_str – str (x)
• print (“my fav num is”), x, “.”, “x =”, x)
• print (“my fav num is ” + x_str + “. ” + “x = ” + x_str)

INPUT/OUTPUT: input (“”)

• prints whatever is within the quotes
• user types in something and hits enter
• returns entered sequence
• can bind that value to a variable so can reference
  • text = input (“Type anything…”)
  • print (5*text)
• input returns a string so must cast if working with numbers
  • num = int (input (“Type a number…”))
  • print (5*num)

IDE’s

• painful to just type things into a shell
• better to have a text editor – integrated development environment (IDE)
  • Idle or Anaconda are examples
• comes with
  • Text editor – use to enter, edit and save your programs
  • Shell – place in which to interact with and run your programs; standard methods to evaluate your programs from the editor or from stored files
  • Integrated debugger (we’ll use later)

Branching programs

• The simplest branching statement is a conditional
  • A test (expresion that evaluates to True or False)
  • A block of code to execute if the test is True
  • An optional block of code to execute if the test is False

Comparison operators on int and float

• i and j are any variable names
  • i>j
  • i>=j
  • i<j
  • i<=j
  • i==j -> equality test, True if i equals j
  • i!=j -> inequality test, True if i not equal to j

Logic operators ON bools

• a and ba are any variable names
• not a -> True if a is False
  • False if a is True
• a and b -> True if both are True
• a or b -> True if either or both are True

Using Control in Loops

• Simple branching programs just make choices, but path through code is still linear
• Sometimes want to reuse parts of the code indeterminate number of times

CONTROL FLOW:

while LOOPS

• while <condition> evaluates to a Boolean
• if <condition> is True, do all the steps inside the while code block
• check <condition> is True, do all steps inside the while code block
• check <condition> again
• repeat until <condition> is False

n = input (“You are in the Lost Forest. Go left or right? ”

while n == “right”:

n = input (“You are in the Lost Forest. Go left or right? “)

print (“You got out of the Lost Forest!”)

Control Flow:

while and for LOOPS

# more complicated with while loop

n = 0

while n < 5:

print (n)

n = n + 1

# shortcut with for loop

for n in range (5) :

print (n)

Control Flow: for Loops

for <variable> in range (<some_num>) :

<expression>

• each time through the loop, <variable> takes a value
• first time, <variable> starts at the smallest value
• next time, <variable> gets the prev value + 1
• etc.

range (start, stop, step)

• default values are start = 0 and step = 1 and is optional
• loop until value is stop -1

mysum = 0

for i in range (7, 10):

mysum += i

print (mysum)

mysum = 0

for i in range (5, 11, 2) :

mysum += i

print (mysum)

break statement

• immediately exits whatever loop it is in
• skips remaining expressions in code block
• exits ony innermost loop

while <condition_1>:

while <condition_2>:

<expression_a>

break

<expression_b>

<expression_c>

break STATEMENT

mysum = 0

for i in range (5, 11, 2):

mysum += i

if mysum == 5:

break

print (mysum)

• what happens in this program?

For loops

• Know number of iterations
• Can end early via break
• uses a counter
• can rewrite a for loop using a while loop

While loops

• unbounded number of iterations
• can end early via break
• can use a counter but must initialize before loop and increment it inside loop
• may not be able to rewrite a while loop using a for loop

text = input (“type something”)

type something “foo”

print (5*text) “foo” “foo” “foo” “foo”

Assume that two variables, varA and varB, are assigned values, either numbers or strings.

Write a piece of Python code that evaluates varA and varB, and then prints out one of the following messages:

• "string involved" if either varA or varB are strings
• "bigger" if varA is larger than varB
• "equal" if varA is equal to varB
• "smaller" if varA is smaller than varB

if type(varA) == str or type(varB) == str:
print(‘string involved’)
elif varA > varB:
print(‘bigger’)
elif varA = varB:
print(‘equal’)
else:
# If none of the above conditions are true,
# it must be the case that varA < varB
print(‘smaller’)

Operator                  Example

=                               c = a + b assigns value of a + b into c

+= Add                     c += a is equivalent to c = c + a

AND

-= Subtract             c-=a is equivalent to c = c – a

AND

*= Multipy               c*= a is equivalent to c = c * a

AND

/= Divide                  c/=a is equivalent to c=c / ac

AND                          /= a is equivalent to c = c %

%=Modulus             c % = a is equivalent to c = c % a

AND

**=Exponent           c **= a is equivalent to c = c**a

AND

//=Floor                   c // = a is equivalent to c = c // a

Division