002-4. List
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# So far, we stored one value into one variable
# Now, we will store multiple values into one variable
# which is called largely collection
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# With keyboard, we can make 4 kinds of brace
# Collection
# list : []
# tuple : ()
# set or dictionary : {}
# we dont use this : <>
a = [1,3,5]
print(a)
# output: [1,3,5]
# Python doesn't have concept of array
# which is one of data structure
# which can be accesed by index
# Instead of array, in Python, we use list as if array
a = [1,3,5]
print(a[0],a[1],a[2])
# output: 1,3,5
a[0]=99
print(a)
# output:
# [99,3,5]
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# Combining iteration statement and list
for i in range(3):
print(a[i])
# But don't write hard coded number 3
for i in range(len(a)):
print(a[i])
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# Quiz
# Make method which retures list
# which is composed of randomly generated 10 numbers
# which are all less than 100
def makeRandoms():
# We should return list containing 10 numbers,
# so, it's not bad choice declaring list initialized by 0
# a = [0, 0, 0, 0, 0, 0, 0, 0, 0, 0]
a = [0]*10
# Parameters of range() :
# 1: starting(default 0)
# 2: ending(default)
# 3: increment and decrement(default 1)
for i in range(10):
a[i] = random.randrange(100)
return a
random.seed(19)
b = makeRandoms()
print(b)
# I refactor above code
def makeRandoms():
# We can start with empty list
# and then we use append() to increase length of list
a = []
# We had to use i from above code
# but we don't need i anymore because we're using empty list
# So, we replace i with placeholder
# for i in range(10):
for _ in range(10):
a.append(random.randrange(100))
return a
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# We can use insert() rather than append()
# to add value between values
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# Quiz
# Make method which returns list
# whose elements are reversed in its order
# 0 1 2 3 4 -> 4 3 2 1 0
# First, make structure
def reverseList(c):
for i in range(len(c)):
c[i]
# Since you should return value,
# you make empty list a=[] and use append()
def reverseList(c):
a = []
for i in range(len(c)):
a.append(c[i])
return a
# And then, we order "reverse order"
def reverseList(c):
a = []
# len(c)-1 means index of last element
# -1 is needed because 0 index is needed
for i in range(len(c)-1, -1, -1):
a.append(c[i])
# Actually reverse order
for i in range(len(a)):
c[i]=a[i]
return a
# Other way by using swap
def reverseList(c):
for i in range(len(c)//2):
# swap ith value from left and ith value from right
c[i], c[len(c)-1-i] = c[len(c)-1-i], c[i]
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