5. Loop

Repeated Steps

while이 if와 다른 점은 condition을 만족하는 한 indent된 구문을 계속해서 다시 실행한다는 것

  • iteration variables : some variable that is changing each time through the loop. iteration variable controls how many times the loop runs

An Infinite Loop

우리는 사실 대부분의 경우 이 무한루프를 원하지 않지. 대부분은 실수야. 무한루프는 절대 끝나지 않는다구!

Another Loop

never run. 단 한 번도 조건을 만족시키지 못한거지. == Zero Loop

Breaking Out of a Loog

The break statement ends the current loop and jumps to the statement immediately following the loop
조건이 끝나는 것 외에 또 다른 loop를 벗어나는 방법이지!

Finishing an Interation with continue

The continue statement ends the current iteration and jumps to the top of the loop and starts the next iteration
이번 iteration은 끝났어! loop를 끝내고 싶지는 않지만 이번 iteration은 끝내고 다음 iteration으로 넘어가고 싶어!

Indefinite Loops

while called indefinite loops because they keep going until a logical condition becomes False
가끔 우리는 그래서 이게 끝날지 아닐지 확신할 수 없지.

Definite Loops

list나 set 같은 것들 finite set. for로 사용할 수 있는 것들. 이것들은 정확한 횟수로 동작하기 때문에 이렇게 불러.
definite loops iterate through the members of a set

Loop Idioms What We Do In Loops

How we construct loops
How we think like a computer

Making smart loops

how to kind of build intelligence into loops

Looping through a Set

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for thing in [9, 41, 12, 3, 74, 15]:
  thing

What is the largest number?

Finding the largest value

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largest_so_far = -1
for thing in [9, 41, 12, 3, 74, 15]:
  if thing > largest_so_far:
    largest_so_far = thing
print largest_so_far

largest_so_far = 9 -> 41 -> 41 -> 41 -> 74 -> 74 (loop 안에서 변화)

Counting in a Loop

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zork = 0
for thing in [9, 41, 12, 3, 74, 15]:
  zork = zork + 1
  print zork, thing
print zork

zork = 1 -> 2 -> 3 -> 4 -> 5 -> 6

Summing in a Loop

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zork = 0
for thing in [9, 41, 12, 3, 74, 15]:
  zork = zork + thing
  print zork, thing
print zork

zork = 9 -> 50 -> 62 -> 65 -> 139 -> 154

Finding the Average in a Loop

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count = 0
sum = 0
for thing in [9, 41, 12, 3, 74, 15]:
  count = count + 1
  sum = sum + thing
print count, sum, sum/count

Filtering in a Loop

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for thing in [9, 41, 12, 3, 74, 15]:
  if thing > 20:
    print 'Large number', thing

Search Using a Boolean Variable

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found = False
for thing in [9, 41, 12, 3, 74, 15]:
  if thing == 3:
    found = True
  print found, value
print found

This means : We found it! There is a three!!!

Finding the largest value & Finding the smallest value

초기값을 어떻게 정하느냐에 따라 값이 이상하게 나올 수 있어. 초기값을 -1로 정하고 loop를 돌았는데 전부 -1보다 크면? 그럼 최소값은 초기값(-1)이 그대로 나올거야. 이건 우리가 원하는 바가 아니지!

None value

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smallest = None
for value in [9, 41, 12, 3, 74, 15]:
  if smallest is None:
    smallest = value
  elif value < smallest:
    smallest = value
print smallest

The is and is not Operators

Don’t start overusing it. It’s at a low level its real meaning is exactly the same as in type and value. Similar to, but stronger than ==

Homework