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This was CS50 - Lecture 6 (Python)

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CS50 week 6，這次要來認識 Python，此篇為課堂筆記。

Built-In Data Types (節錄自 Notes)

  • bool, True or False
  • float, real numbers
  • int, integers
  • str, strings
  • range, sequence of numbers
  • list, sequence of mutable values, or values we can change
    • like arrays in C, can grow and shrink automatically in Python
  • tuple, collection of ordered values like x- and y-coordinates, or longitude and latitude
  • dict, dictionaries, collection of key/value pairs, like a hash table, constant time: O(1)
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from cs50 import get_string
people = {
    "Tom": "tom@123.com",
    "Mary": "mary@123.com"
}
name = get_string("name:") # type "Tom"
if name in people:
    print(f"Email: {people[name]}")
#Email:tom@123.com
  • set, collection of unique values, or values without duplicates

Examples

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from cs50 import get_string

answer = get_string("What's your name?") #type "Tom"
print(f"Hello, {answer}") #Hello, Tom
  • f: format string，可以在字串裡使用變數，變數需要使用 {}
  • 每一行的最後面可以不打 semicolon
  • 變數前不用宣告 data type，type 由數值定義，python 是 loosely type 的語言。
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for i in [1,2,3]:
    print(i) 
# 1
# 2
# 3

class range(start, stop[, step])
Official Doc - range()

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for i in range(0, 10, 2):
    print(i)
#0
#2
#4
#6
#8
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answer = input("What's your name?") # type "Tom"
print(f"Hi, {answer}")# Hi, Tom
  • input: prompt questions
    • python 內建的語法，與 cs50 library 中的 get_string 相等作用
  • string 使用 single quote '' 或是 double quotes "" 都可以
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x = int(input("x:")) #1
y = int(input("y:")) #2

print(x / y) #0.5
  • 注意 input("x:") 輸入的值為 string，要加 int 轉型成數字。
  • 在 python 中，每一個東西都是 Object
    • Objects 是 第一等公民
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for i in range(4):
    print("*", end="") #****

相當於以下

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print("*"*4) #****
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for i in range(3):
    for x in range(3):
        print("*", end="")
    print() # add a new line
# ***
# ***
# ***
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scores = [1,2,3]
print(f"Average: {int(sum(scores)/ len(scores))}")
#Average: 2
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scores = []
for i in range(3):
    scores.append(i) #scores = [0,1,2]

print(f"Average:  {sum(scores)/ len(scores)}") #Average: 1.0
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ints = [1,2]
if 1 in ints:
    print("Found 1!")
else:
    print("Not Found.")
#Found 1!

輕鬆做到 SWAP

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x=1
y=2

print(f"x is {x}, y is {y}") #x is 1, y is 2
x, y = y, x
print(f"x is {x}, y is {y}") #x is 2, y is 1