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PYPL Index Shows Top 3: Python, Java, JavaScript

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The Beauty and Joy of Computing��Python�Higher-Order Functions�

https://pypl.github.io/PYPL.html

CS10 TA

Marius Castro

(Baby version)

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The Beauty and Joy of Computing : Python IV HOFs (1)

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Higher Order Functions…�Why? Basics…

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The Beauty and Joy of Computing : Python IV HOFs (2)

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Why Use Functions? (review)

Calling it…

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The Beauty and Joy of Computing : Python IV HOFs (3)

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The Beauty and Joy of Computing : Python IV HOFs (3)

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Why Use Functions? (review, in Python)

Calling it…

pd()

for _ in range(4):

fd(25)

rt(90)

pu()

pd()

for _ in range(4):

fd(100)

rt(90)

pu()

pd()

for _ in range(4):

fd(200)

rt(90)

pu()

def draw_square(length): � pd()

for _ in range(4):

fd(length)

rt(90)

pu()

draw_square(100)

from turtle import *

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The Beauty and Joy of Computing : Python IV HOFs (4)

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Why Use Higher-Order Functions?

Calling it…

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The Beauty and Joy of Computing : Python IV HOFs (5)

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Why Use Higher-Order Functions? (Python)

for _ in range(4):

draw_line(100)

rt(90)

for _ in range(4):

draw_dashed_line(100)

rt(90)

for _ in range(4):

draw_wiggly_line(100)

rt(90)

def draw_100_square(line_drawer): � pd()

for _ in range(4):

line_drawer(100)

rt(90)

pu()

Calling it…

draw_100_square(draw_wiggly_line)

from turtle import *

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The Beauty and Joy of Computing : Python IV HOFs (6)

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Why HOFs are like Pregnant Fish, Sharks

Source: Brian Harvey, Wikipedia (Fbattail, Aka, Evdaimon)

Data (e.g,. Sentences, Words, Booleans, Lists)

Data (e.g,. Sentences, Words, Booleans, Lists)

Data (e.g,. Sentences, Words, Booleans, Lists)

Normal �Fish

Data (e.g,. Sentences, Words, Booleans, Lists)

Functions

Pregnant�Fish

Sharks

Functions

Pregnant

Sharks

Functions

Functions

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The Beauty and Joy of Computing : Python IV HOFs (7)

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HOFs you have seen before

  • [Reporter(e) for e in theList if Predicate(e)]
    • map Reporter over List
      • Report a new list, every element E of theList �becoming Reporter(E)
    • keep items Predicate from List
      • Report a new list, keeping only elements E of� theList if Predicate(E)

​

  • from functools import reduce
  • reduce(Combiner, theList)
    • combine List using Combiner
      • Combine all the elements of List with �Combiner(E1, E2) for elements E1,E2 of theList

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How combine works:

a

b

c

d

f(_,_) [‘a’,’b’,’c’,’d’]

reduce(Combiner, theList)

a b

​

f(a,b) c

​

f(f(a,b),c) d

​

​

f(f(f(a,b),c),d)

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The Beauty and Joy of Computing : Python IV HOFs (9)

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combine above the abstraction line

Your f should be associative, and work if it’s

a f b f c f d

combine using f

((a f b) f (c f d))

or…

(((a f b) f c) f d)

etc…

(a b c d)

🗹

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The Beauty and Joy of Computing : Python IV HOFs (10)

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(Cal) Clicker Question

What is reported here?

​

  1. abcd
  2. acdb
  3. bdac
  4. dcba
  5. (nothing)

​

def joinswap(L, R):

return R + L

​

reduce(joinswap, "abcd")

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The Beauty and Joy of Computing : Python IV HOFs (11)

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Acronym

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Acronym Algorithm

(the Beauty and Joy of Computing)

keep only �uppercase words

(Beauty Joy Computing)

map first letter only

(B J C)

combine into one�word (join)

BJC

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The Beauty and Joy of Computing : Python IV HOFs (13)

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The Beauty and Joy of Computing : Python IV HOFs (13)

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Acronym (uses map, keep, combine)

🗹

def Acronym(phrase):

return ''.join([w[0] for w in phrase.split() if w < 'a'])

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The Beauty and Joy of Computing : Python IV HOFs (14)

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The Beauty and Joy of Computing : Python IV HOFs (14)

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(Cal) Clicker Question

What is reported if I swap keep and map in Acronym and call it on (the Beauty and Joy of Computing)?

  1. bjc
  2. BJC
  3. CJB
  4. (nothing)
  5. Error

​

def Acronym(phrase):

return ''.join([l for l in [w[0] for w in phrase.split()] if l < 'a'])

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The Beauty and Joy of Computing : Python IV HOFs (15)

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HOF Tools & Demo

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HOF tools, sharks, pregnant fish, mymap

🗹

lambda

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The Beauty and Joy of Computing : Python IV HOFs (17)

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Frankenstein … can we get laclacc?

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