CS 330 - Artificial Intelligence - Python in one week I Instructor: - - PowerPoint PPT Presentation

CS 330 - Artificial Intelligence

• Python in one week I

Instructor: Renzhi Cao Computer Science Department Pacific Lutheran University Fall 2019 1

Materials adopted from Kaggle

Announcement

• Course website login
• Finish course survey by today (especially your

interested topic and programming experience)

• Read materials on course website

2

• Python programming and industry experience of

learning new programming language in a week

• Progress on topics for final project? Final report
• n Archive?

• 10:30 am
• Monday
• Sept 16
• Morken 132

https://www.plu.edu/communication/life-under-drones/ Panel: “Horizons in Emerging Tech: Drone Innovations in Engineering, Medicine, Library Science, and the Humanities”

• n Thursday 9.19 from 9 - 9:50 am

Extra course participation credit - Providing pictures or writing summaries on Sakai!

Overview

• Learning Python in a week

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• Python VS JAVA

Hello World example

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#javac HelloWorld.java #java HelloWorld #python Hello.py

Two different kind of high-level languages

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• Interpreters
• Compilers

Python introduction

Command mode VS script mode

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#python #print 1+1 Create hi.py, and write statement: print 1+1 #python hi.py

Python introduction

• syntax, variable assignment, numbers
• functions and getting help
• booleans and conditionals
• lists and objects
• loops and list comprehensions
• strings and dictionaries
• files and trees

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Python introduction

• syntax, variable assignment, numbers
• functions and getting help
• booleans and conditionals
• lists and objects
• loops and list comprehensions
• strings and dictionaries
• files and trees

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Syntax, variable assignment, numbers

• Python was named for the British comedy troupe Monty

Python (https://en.wikipedia.org/wiki/Monty_Python)

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spam_amount = 0 print(spam_amount) # Ordering Spam, egg, Spam, Spam, bacon and Spam (4 more servings of Spam) spam_amount = spam_amount + 4 if spam_amount > 0: print("But I don't want ANY spam!") viking_song = "Spam " * spam_amount print(viking_song) Read the following, think and share output with your neighbors (2 mins)

Syntax, variable assignment, numbers

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• spam_amount = 0

variable assignment!!!

(1 min) What is different from other languages (JAVA?). Think and share with your neighbors

• No variable “declare”
• No variable type

Syntax, variable assignment, numbers

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• print(spam_amount)

function call!!!

• # Ordering Spam, egg, Spam, Spam, bacon and Spam (4

more servings of Spam) spam_amount = spam_amount + 4 Re-assignment!!!

Syntax, variable assignment, numbers

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• if spam_amount > 0:

print("But I don't want ANY spam!") What is the output? What is different from JAVA?

• Colon (:)
• Indented (4 spaces), no curly brace

Syntax, variable assignment, numbers

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• viking_song = "Spam " * spam_amount
• print(viking_song)

What is the output?

Numbers and arithmetic in Python

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• spam_amount = 0

numbers and arithmetic

Try it: #python #spam_amount = 0 #type(spam_amount) Try it: #python #spam_amount = 0.0 #type(spam_amount)

Numbers and arithmetic in Python

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Arithmetic

Numbers and arithmetic in Python

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• True division and floor division

Think about the different from JAVA?

print(5 / 2) print(6 / 2) print(5 // 2) print(6 // 2)

Numbers and arithmetic in Python

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• Order of operations

PEMDAS - Parentheses, Exponents, Multiplication/Division, Addition/Subtraction

8 - 3 + 2

• 3 + 4 * 2

s1 = 5 s2 = 11 # now I want average score aveS = s1 + s2/2 print(aveS) aveS = (s1 + s2)/2 print(aveS)

Numbers and arithmetic in Python

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• Builtin functions for working with numbers

min, max, abs, int, float

print(min(1, 2, 3)) print(max(1, 2, 3)) how about more numbers? print(abs(32)) print(abs(-32)) print(float(10)) print(int(3.33)) # They can even be called on strings! print(int('807') + 1)

Exercise

• Try: CS330_ex1.py

Python introduction

• syntax, variable assignment, numbers
• functions and getting help
• booleans and conditionals
• lists and objects
• loops and list comprehensions
• strings and dictionaries
• files and trees

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Functions and getting help

functions: calling them, defining them, and looking them up using Python's built-in documentation.

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Think: how we define function in JAVA? In JAVA, functions take a specific number of arguments, each having a particular type: public String print(String s) { System.out.println(s); } Call function: print(“hello”)

Functions and getting help

Python functions are allowed much more flexibility

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print("The print function takes an input and prints it to the screen.") print("Each call to print starts on a new line.") print("You'll often call print with strings, but you can pass any kind of

• value. For example, a number:")

print(2 + 2) print("If print is called with multiple arguments...", "it joins them", "(with spaces in between)", "before printing.") print('But', 'this', 'is', 'configurable', sep='!...') print() print("^^^ print can also be called with no arguments to print a blank line.")

Functions and getting help

If you forgot what a function is doing, what to do? For example, what abs is doing?

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In JAVA, you could read JAVA Doc. In Python, you could use help() function: help(abs) —— not help(abs(-2)) help(print)

Functions and getting help

How to define a function in Python?

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def least_difference(a, b, c): diff1 = abs(a - b) diff2 = abs(b - c) diff3 = abs(a - c) return min(diff1, diff2, diff3)

Functions and getting help

How to call function in Python?

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least_difference(1, 10, 100) print( least_difference(1, 10, 100), least_difference(1, 10, 10), least_difference(5, 6, 7), # Python allows trailing commas in argument lists. How nice is that? )

Functions and getting help

help(least_difference) # what do you find?

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Docstrings: def least_difference(a, b, c): """Return the smallest difference between any two numbers among a, b and c. >>> least_difference(1, 5, -5) 4 """ diff1 = abs(a - b) diff2 = abs(b - c) diff3 = abs(a - c) return min(diff1, diff2, diff3)

Functions and getting help

now if you type: help(least_difference), you will find:

Help on function least_difference in module __main__: least_difference(a, b, c) Return the smallest difference between any two numbers among a, b and c. >>> least_difference(1, 5, -5) 4

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Functions and getting help

What would happen if we didn't include the return keyword in our function?

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def least_difference(a, b, c): """Return the smallest difference between any two numbers among a, b and c. """ diff1 = abs(a - b) diff2 = abs(b - c) diff3 = abs(a - c) min(diff1, diff2, diff3) print( least_difference(1, 10, 100), least_difference(1, 10, 10), least_difference(5, 6, 7), )

None None None The same: mystery = print() print(mystery)

Functions and getting help

Default arguments for function in Python: When we called help(print), we saw that the print function has several optional arguments. For example, we can specify a value for sep to put some special string in between our printed arguments: print(1, 2, 3, sep=' < ‘) and print(1, 2, 3)

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Functions and getting help

Adding optional arguments with default values to the functions in Python: def greet(who="Colin"): print("Hello,", who) greet() greet(who="Dr. Cao") # (In this case, we don't need to specify the name of the argument, because it's unambiguous.) greet("world")

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Functions and getting help

Functions are objects too: def f(n): return n * 2 x = 12.5 In this case, x refers to an object of type float, and f refers to an object of type:

print( type(x), type(f), sep='\n' ) print(x) print(f)

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Functions and getting help

we can call the function we receive as an argument:

def f(n): return n * 2 def call(fn, arg): """Call fn on arg""" return fn(arg) def squared_call(fn, arg): """Call fn on the result of calling fn on arg""" return fn(fn(arg)) print( call(f, 1), squared_call(f, 1), sep='\n', # '\n' is the newline character - it starts a new line )

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Functions and getting help By default, max returns the largest of its arguments. But if we pass in a function using the optional key argument, it returns the argument x that maximizes key(x) (aka the 'argmax').

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def mod_5(x): """Return the remainder of x after dividing by 5""" return x % 5 print( 'Which number is biggest?', max(100, 51, 14), 'Which number is the biggest modulo 5?', max(100, 51, 14, key=mod_5), sep='\n', ) Which number is biggest? 100 Which number is the biggest modulo 5? 14

Functions and getting help Lambda functions for short throwaway function whose body fits into a single line.

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def mod_5(x): """Return the remainder of x after dividing by 5""" return x % 5 mod_5 = lambda x: x % 5 # Lambdas can take multiple comma-separated arguments abs_diff = lambda a, b: abs(a-b) print("Absolute difference of 5 and 7 is", abs_diff(5, 7)) # Or no arguments always_32 = lambda: 32 always_32()

Functions and getting help Some times you could use lambdas to solve complex questions in single line:


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# Preview of lists and strings. (We'll go in depth into both soon) # - len: return the length of a sequence (such as a string or list) # - sorted: return a sorted version of the given sequence (optional key # function works similarly to max and min) # - s.lower() : return a lowercase version of string s names = ['jacques', 'Ty', 'Mia', 'pui-wa'] print("Longest name is:", max(names, key=lambda name: len(name))) # or just key=len print("Names sorted case insensitive:", sorted(names, key=lambda name: name.lower()))

Exercise

• Try: CS330_ex2.py

Python introduction

• syntax, variable assignment, numbers
• functions and getting help
• booleans and conditionals
• lists and objects
• loops and list comprehensions
• strings and dictionaries
• files and trees

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Booleans and conditionals

Python has a type bool which can take on one of two values: True and False.

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x = True print(x) print(type(x))

Booleans and conditionals

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Rather than putting True or False directly in our code, we usually get boolean values from boolean operators. Yes or no questions.

Booleans and conditionals

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def can_run_for_president(age): """Can someone of the given age run for president in the US?""" # The US Constitution says you must "have attained to the Age of thirty-five Years" return age >= 35 print("Can a 19-year-old run for president?", can_run_for_president(19)) print("Can a 45-year-old run for president?", can_run_for_president(45))

Booleans and conditionals

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• Comparisons are a little clever

3.0 == 3

• Comparisons are not too clever

‘3’ == 3 True False

Booleans and conditionals

Comparison operators can be combined with the arithmetic operators

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def is_odd(n): return (n % 2) == 1 print("Is 100 odd?", is_odd(100)) print("Is -1 odd?", is_odd(-1))

Booleans and conditionals

• Python provides operators to combine boolean values

using the standard concepts of "and", "or", and "not". And in fact, the corresponding Python operators use just those words: and, or, and not.

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Combining Boolean Values

def can_run_for_president(age, is_natural_born_citizen): """Can someone of the given age and citizenship status run for president in the US?""" # The US Constitution says you must be a natural born citizen *and* at least 35 years old return is_natural_born_citizen and (age >= 35) print(can_run_for_president(19, True)) print(can_run_for_president(55, False)) print(can_run_for_president(55, True))

Booleans and conditionals

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What should be this?

True or True and False Python has precedence rules that determine the order in which operations get evaluated in expressions like above. For example, and has a higher precedence than or, which is why the first expression above is True.

Booleans and conditionals

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Bug code: prepared_for_weather = have_umbrella or rain_level < 5 and have_hood or not rain_level > 0 and is_workday Good code: prepared_for_weather = have_umbrella or (rain_level < 5 and have_hood)

• r not (rain_level > 0 and is_workday)

Alternative way: prepared_for_weather = ( have_umbrella

• r ((rain_level < 5) and have_hood)
• r (not (rain_level > 0 and is_workday))

)

Booleans and conditionals

booleans really start to shine when combined with conditional statements, using the keywords if, elif, and else.

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def inspect(x): if x == 0: print(x, "is zero") elif x > 0: print(x, "is positive") elif x < 0: print(x, "is negative") else: print(x, "is unlike anything I've ever seen...") inspect(0) inspect(-15)

Booleans and conditionals

• Cautions about indentation

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def f(x): if x > 0: print("Only printed when x is positive; x =", x) print("Also only printed when x is positive; x =", x) print("Always printed, regardless of x's value; x =", x) f(1) f(0)

Booleans and conditionals

Data type conversion:

• We've seen int(), which turns things into ints, and

float(), which turns things into floats, so you might not be surprised to hear that Python has a bool() function which turns things into bools.

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print(bool(1)) # all numbers are treated as true, except 0 print(bool(0)) print(bool("asf")) # all strings are treated as true, except the empty string "" print(bool("")) # Generally empty sequences (strings, lists, and other types we've yet to see like lists and tuples) # are "falsey" and the rest are "truthy"

Booleans and conditionals

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if 0: print(0) elif "spam": print("spam")

Booleans and conditionals

Conditional expressions

Setting a variable to either of two values depending on some condition is a pretty common pattern.

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def quiz_message(grade): if grade < 50:

• utcome = 'failed'

else:

• utcome = 'passed'

print('You', outcome, 'the quiz with a grade of', grade) quiz_message(80) def quiz_message(grade):

• utcome = 'failed' if grade < 50 else 'passed'

print('You', outcome, 'the quiz with a grade of', grade) quiz_message(45)

Exercise

• Try: CS330_ex3.py

Questions?

• Submit your in-class exercises