List
컴퓨터에서 ‘여러개’라는건 0 또는 하나 이상 list에는 아무것도 안들수도, 하나가 들어있을수도, 하나이상이 들어 있을 수 있음 list is a ‘collection’ of values
l = [1,2,3] -> list에 값을 하나씩 집어넣음
l = list([1,2,3]) -> list를 집어놓고 list를 만들라고 한것 -> list
l = [x in range(10)] ->set builder
list can hold another list
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x = [1,2,3]
y = [1,2,x]
y
[1,2,[1,2,3]]
list can be modified
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x.append(4)
x
[1,2,3,4]
append : x리스트에 값을 추가하라
. operator => method call 이라 부름
그럼 이것도 가능한가?
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l = 3
l.append(4)
---------------------------------------------------------------------------
AttributeError Traceback (most recent call last)
<ipython-input-7-dcf28f8b6fcf> in <module>()
----> 1 l.append(4)
AttributeError: 'int' object has no attribute 'append'
integer 값을 두개를 append할 수는 없음 append는 list값에만 수행될 수 있는것
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x = (3,4)
x.append(5)
---------------------------------------------------------------------------
AttributeError Traceback (most recent call last)
<ipython-input-8-399ca43270b6> in <module>()
1 x = (3,4)
----> 2 x.append(5)
AttributeError: 'tuple' object has no attribute 'append'
tupple은 list처럼 값의 모임인데 append 왜 앙대지?
=> tupple은 변경될 수 없기 때무니딩
A Python solution
A python program to solve a problem?
- Enter input
- Print (display) output
How to create a Python solution?
- Find a set of example values to compute
- Store them in variables
- Do computation on variables
- Benefit? -> Generalization
Problem solving example
1)
If you run a 10 kilometer race in 43 minutes 30 seconds, what is your average time per mile? What is your average speed in miles per hour? (Hint: there are 1.61 kilometers in a mile).
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sec = 43 * 60 + 30
km = 10
mile = km / 1.61
milepersec = mile / sec
mileperhour = milepersec*3600
mileperhour
8.567144998929106
Define a function to compute the speed in miles per hour given the distance in km and the time in seconds.
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def convert_speed(km, sec) :
...
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sec = 43 * 60 + 30
km = 10
def convert_speed(km, sec) :
mile = km / 1.61
milepersec = mile / sec
mileperhour = milepersec*3600
return mileperhour
convert_speed(km,sec)
8.567144998929106
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km = 10
m = 43
s = 30
def minsec(m, s) :
totalsec = m * 60 + s
return totalsec
def convert_speed(km, sec) :
mile = km / 1.61
milepersec = mile / sec
mileperhour = milepersec*3600
return mileperhour
convert_speed(km,minsec(43,30))
8.567144998929106
2)
The volume of a sphere with radius r is 4/3πr³. What is the volume of a sphere with radius 5?
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import math
r = 5
vol = 4/3 * math.pi * r ** 3
3)
The area of a circle with radius r is πr². What is the value of a sphere with radius 3.4?
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import math
r = 3.4
area = math.pi*r**2
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def circle_area(r):
return math.pi*r ** 2
print(circle_area(3.4))
What if we increase the radius by 0.7?
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import math
print(circle_area(3.4))
print(circle_area(3.4 + 0.7))
What about using a variable r?
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import math
r = 3.4
print(circle_area(r))
r += 0.7
print(circle_area(r))
=> is this concept generalizable?
use class!
class
Circle 이라는 class를 만들어서 반지름을 넣으면 원이 만들어 지는 함수를 정의함
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class Circle:
def __init__(self,r):
self.r = r
x = Circle(1)
x.r
1
self 대신 아무렇게나 써서 해도 됨
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class Circle:
def __init__(elmo,r):
elmo.r = r
x = Circle(1)
x.r
1
하지만 파이썬에서는 self라는 걸 많이 사용함 (편의상)
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class Circle:
def __init__(self,r):
self.r = r
def area(self):
return math.pi*self.r**2
x = Circle(1)
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x.r
1
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x.area()
3.14
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class Circle:
def __init__(self,r):
self.r = r
def area(self):
return math.pi**2 * self.r
def inc_r(self, d):
self.r += d
c = Circle(3.4)
print(c.area())
c.inc_r(0.7)
print(c.area())
36.316811075498 52.81017250684442
