Python Basics

tags: `Python`

Expression & Variables

Data Types

String
Float
Integer
Booleank

print("Sting")  #String
print(7 + 8)    #15
print(7 + "8")  #TypeError

# 使用 type() 查詢 data types
print(type("a"))  #<class 'str'>
print(type(2))  #<class 'int'>
print(type(2.5))  #<class 'float'>

String

below are string method

string indexing

name = "Jalen"
print(name[1]  # a
print(name[0]) # J

# check the position of the elements in a string
name.index("l")  # 2
pets = "Cats & Dogs"
pets.index("Dog")  # 7
pets.index("s")  # 3，雖然有兩個s，只會返回第一個 s 的所在位置

# check if the element is in a string
"Dragons" in pets. #因為 pets 內沒有 Dragon，顯示 False

slice

fruit = "Pineapple"
print(fruit[:4])  #Pine
print(friut[4:])  #apple

create new string

message = "A kong string with a silly typo"
message[2] = "l"  #error, 因為 string is immutable，需用以下方式

new_message = message[0:2] + "l" + mssage[3:]
#correct, result: A long string with a silly typo

upper and lower

"Mountains".upper()  #MOUNTAINS
"Mountains".lower()  #mountains

strip 篩除空格／lstrip 刪除左方空格／rstrip 刪除右方空格

" yes ".strip()  #'yes'
" yes ".lstrip() #'yes '
" yes ".rstrip() #' yes'

count 計算字串內的字母數量

"The number of times e occurs in this string is 4".count("e")

#result: 4

endswith 檢查 String 的結尾

"Forest".endswith("rest")  #True

isnumeric 檢查 string 是否都是數字

"Forest".isnumeric() #False
"12345".isnumeric()  #True

int 將 string 轉換成數字

int('12345') + int('54321')
# 66666
# 因為 12345 + 54321 = 66666

join 插入

" ".join(["This", "is", "test."])
# This is test.

"......".join(["This", "is". "test."])
# This......is......test.

split 分割

"This is another example".split()
#['This', 'is', 'another', 'example']

formatting strings
比 str() 更好用的 string 轉換器

name = "Manny"
number = leng(name) * 3
print("Hello {}, your lucky number is {}".format(name, number))

# Hello Manny, your lucky number is 15


# formatting example: set the position in {}
print("Your lucky number is {number}, {name}.".format(name=name, number=len(name)*3))

# Your lucky number is 15. Manny.


#formatting expression
price = 7.5
with_tax = price * 1.09
print(price, with_tax)  #7.5 8.175

print("Base price: ${:.2f}. With Tax: ${:.2f}".format(price, with_tax))
# Base price: $7.50. With Tax: $8.18
# 表示改為 float 且四捨五入顯示兩位數

EXAMPLES of String










































































































#EXAMPLE 1
def double_word(word):
    length = len(word*2)
    return word*2 + str(length)

print(double_word("hello")) # Should return hellohello10
print(double_word("abc"))   # Should return abcabc6
print(double_word(""))      # Should return 0


#EXAMPLE 2
def first_and_last(message):
    if message == "" or message[0] == message[-1]:
      return True
    return False

print(first_and_last("else"))
print(first_and_last("tree"))
print(first_and_last(""))

#result: 如果第一個字母與最後一個字母相同／“”，回傳 True, 否則回傳 False


#EXAMPLE 3: 替換email，以新domain取代舊domain
def replace_domain(email, old_domain, new_domain):
    if "@" + old_domain in email:
        index = email.index("@" + old_domain)
        new_email = email[:index] + "@" + new_domain
        return new_email
    return email
    

#EXAMPLE 4
def initials(phrase):
    words = phrase.split()
    result = ""
    for word in words:
        result += word[0].upper()
    return result

print(initials("Universal Serial Bus")) # Should be: USB
print(initials("local area network")) # Should be: LAN
print(initials("Operating system")) # Should be: OS


#EXAMPLE 5
def to_celsius(x):
    return (x-32)*5/9

for x in range(0, 101, 10):
    print("{:>3} F | {:>6.2f} C".format(x, to_celsius(x)))
    
#result
#   0 F | -17.78 C
#  10 F | -12.22 C
#  20 F |  -6.67 C
#  30 F |  -1.11 C
#  40 F |   4.44 C
#  50 F |  10.00 C
#  60 F |  15.56 C
#  70 F |  21.11 C
#  80 F |  26.67 C
#  90 F |  32.22 C
# 100 F |  37.78 C


#EXAMPLE 6: 互文
def is_palindrome(input_string):
	# We'll create two strings, to compare them
	new_string = ""
	reverse_string = ""
	# Traverse through each letter of the input string
	for x in input_string.upper():
		# Add any non-blank letters to the 
		# end of one string, and to the front
		# of the other string. 
		if x != " ":
			new_string = new_string + x
			reverse_string = x + reverse_string
	# Compare the strings
	if new_string == reverse_string:
		return True
	return False

print(is_palindrome("Never Odd or Even")) # Should be True
print(is_palindrome("abc")) # Should be False
print(is_palindrome("kayak")) # Should be True


#EXAMPLE 7
def pig_latin(text):
  say = ""
  # Separate the text into words
  words = text.split()
  a = []
  for word in words:
    # Create the pig latin word and add it to the list
    say = word[1:]+ word[0] + "ay"
    a.append(say)
    # Turn the list back into a phrase
  return " ".join(a)
		
print(pig_latin("hello how are you")) # Should be "ellohay owhay reaay ouyay"
print(pig_latin("programming in python is fun")) # Should be "rogrammingpay niay ythonpay siay unfay"

Lists & Tuples

x = ["Now", "we", "are"]

check the list length len(x)
check if the element is in the list "are" in x
- check the spesific position in the list print(x[0])
List 與 String 同屬於sequence，都能使用
- for elemrnt in sequence
- sequence[x]
- len(sequence)
- sequence + sequence
- element in sequence
lists 與 string 的不同點在於：lists is mutable(能直接在list內更改element)

enumerate

winners = ["Ashley", "Dylan", "Reese"]
for index, person in enumerate(winners):
    print("{} - {}".formate(index+1, person))

# 1 - Ashley
# 2 - Dylan
# 3 - Reese

list comprehension

multiple = []
for x in range(1, 11):
    multiples.append(x*7)

print(multiples)
#[7, 14, 21, 28, 35, 42, 49, 56, 63, 70]

#list comprehension can do it in one-line
multiples = [x*7 for x in range(1, 11)]
print(multiples)
#[7, 14, 21, 28, 35, 42, 49, 56, 63, 70]

languages = ["Python", "Perl", "Ruby", "Go"]
lengths = [len(language) for langue in langues]
print(lengths)
# [6, 4, 4, 2]

# 從 1-100 中找出 3 的倍數
z = [x for x in range(0, 101) if x % 3 == 0]
print(z)
#[0, 3, 6, 9, 12, 15, 18, 21, 24, 27, 30, 33, 36, 39, 42, 45, 48, 51, 54, 57, 60, 63, 66, 69, 72, 75, 78, 81, 84, 87, 90, 93, 96, 99]

x = ["Now", "we", "are"]

len(x) #3
"are" in x  #True
x[0]  #'Now'
x[1:3]  #['We', 'are']
x[:2]  #['Now', 'we']
x[2:]  #['are']

Modify The Content Of A List

.append("element")
.insert(index, "element")
.remove("element")
.pop(index)

fruits = ["pineapple", "banana", "apple", "melon"]

friuts.append("kiwi")
# fruits = ["pineapple", "banana", "apple", "melon", "kiwi"]

fruits.insert(0, "orange")
# fruits = ["orange", "pineapple", "banana", "apple", "melon", "kiwi"]

#即使 insert 的位置超過 lists 也能用
friuts.insert(100, "grape")
# fruits = ["orange", "pineapple", "banana", "apple", "melon", "kiwi", "grape"]

fruites.remove("melon")
# fruits = ["orange", "pineapple", "banana", "apple", "kiwi", "grape"]

fruites.pop(3)
# 原本的 fruits = ["orange", "pineapple", "banana", "apple", "kiwi", "grape"]
# 第 3 個位置的元素會被拿掉
# fruits = ["orange", "pineapple", "banana", "kiwi", "grape"]

fruites[2] = "strawberry"
# 原本的 fruits = ["orange", "pineapple", "banana", "kiwi", "grape"]
# 第 ２ 個位置會被 strawberry 取代
# fruits = ["orange", "pineapple", "strawberry", "kiwi", "grape"]

Lists And Tuples

Tuple 的特色

順序性
elements 可以是任何資料型態
immutable，不可改變
tuple 的「位置順序」是有意義的
fruits = ['apple', 'pineapple', 'melon'] 是 string
fruits = ('apple', 'pineapple', 'melon') 是 tuple

使用 unpack 方式分割 tuple

def convert_seconds(seconds):
    hours = seconds // 3600
    minutes = (seconds - hours * 3600)//60
    remaining_seconds = seconds - hours * 3600 - minutes * 60
    return hours, minutes, remaining_seconds

result = convert_seconds(5000)
type(result) #<class 'tuple'>
print(result) # (1, 23, 20)

# 以 unpack 方式分割 tuple
hours, minutes, seconds = result
print(hours, minutes, seconds) # 1 23 20

EXAMPLES of Lists & Tuple




































































#EXAMPLE 1
def group_list(group, users):
    members = ",".join(users)
    return group + ": " + members

print(group_list("Marketing", ["Mike", "Karen", "Jake", "Tasha"])) # Should be "Marketing: Mike, Karen, Jake, Tasha"
print(group_list("Engineering", ["Kim", "Jay", "Tom"])) # Should be "Engineering: Kim, Jay, Tom"
print(group_list("Users", "")) # Should be "Users:"


#EXAMPLE 2: lisrs 間隔列印
def skip_elements(elements):
	# code goes here
  new_elements = []
  length = len(elements)
  
  for i in range(0, length, 2):
    new_elements.append(elements[i])
  return new_elements

print(skip_elements(["a", "b", "c", "d", "e", "f", "g"])) # Should be ['a', 'c', 'e', 'g']
print(skip_elements(['Orange', 'Pineapple', 'Strawberry', 'Kiwi', 'Peach'])) # Should be ['Orange', 'Strawberry', 'Peach']
print(skip_elements([])) # Should be []


#EXAMPLE 3 unpack tuple
#guest_list(('Ken', 30, "Chef"), ("Pat", 35, 'Lawyer'), ('Amanda', 25, "Engineer"))

def guest_list(guests):
	for guest in guests:
		name, age, role  = guest
		print("{name} is {age} years old and works as {role}".format(name=name, age=age, role=role))

#guest_list([('Ken', 30, "Chef"), ("Pat", 35, 'Lawyer'), ('Amanda', 25, "Engineer")])


#EXAMPLE 4: List's enumerate
def skip_elements(elements):
	new_elements = []
	for index, element in enumerate(elements):
	  if index % 2 == 0:
	    new_elements.append(element)
	
	return new_elements

print(skip_elements(["a", "b", "c", "d", "e", "f", "g"])) # Should be ['a', 'c', 'e', 'g']
print(skip_elements(['Orange', 'Pineapple', 'Strawberry', 'Kiwi', 'Peach'])) # Should be ['Orange', 'Strawberry', 'Peach']


#EXAMPLE 5: enter a bunch of email and name as a list

def full_emails(people):
    result = []
    for email, name in people:
        result.append("{} <{}>".formate(name, email))
    return result
    
print(full_emails(['tcmiss@gmail.com', 'TC Huang'], ['brian@gmail.com', 'Brian Wu']))

#['TC Huang <tcmiss@gamil.com>', 'Brian Wu <brian@gmail.com>']


#EXAMPLE 6
def skip_elements(elements):
	return [element for element in elements if elements.index(element) % 2 == 0]  

print(skip_elements(["a", "b", "c", "d", "e", "f", "g"])) # Should be ['a', 'c', 'e', 'g']
print(skip_elements(['Orange', 'Pineapple', 'Strawberry', 'Kiwi', 'Peach'])) # Should be ['Orange', 'Strawberry', 'Peach']

Common sequence operations

len(sequence) Returns the length of the sequence
for element in sequence Iterates over each element in the sequence
if element in sequence Checks whether the element is part of the sequence
sequence[i] Accesses the element at index i of the sequence, starting at zero
sequence[i:j] Accesses a slice starting at index i, ending at index j-1. If i is omitted, it's 0 by default. If j is omitted, it's len(sequence) by default.
for index, element in enumerate(sequence) Iterates over both the indexes and the elements in the sequence at the same time

List-specific operations and methods

list[i] = x Replaces the element at index i with x
list.append(x) Inserts x at the end of the list
list.insert(i, x) Inserts x at index i
list.pop(i) Returns the element a index i, also removing it from the list. If i is omitted, the last element is returned and removed.
list.remove(x) Removes the first occurrence of x in the list
list.sort() Sorts the items in the list
list.reverse() Reverses the order of items of the list
list.clear() Removes all the items of the list
list.copy() Creates a copy of the list
list.extend(other_list) Appends all the elements of other_list at the end of lis

List comprehension

[expression for variable in sequence] Creates a new list based on the given sequence. Each element is the result of the given expression.
[expression for variable in sequence if condition] Creates a new list based on the given sequence. Each element is the result of the given expression; elements only get added if the condition is true.

Dictionaries

x = {"key":value, "key2":value2}

Operations

len(dictionary) - Returns the number of items in the dictionary
for key in dictionary - Iterates over each key in the dictionary
for key, value in dictionary.items() - Iterates over each key,value pair in the dictionary
if key in dictionary - Checks whether the key is in the dictionary
dictionary[key] - Accesses the item with key key of the dictionary
dictionary[key] = value - Sets the value associated with key
del dictionary[key] - Removes the item with key key from the dictionary

Methods

dict.get(key, default) - Returns the element corresponding to key, or default if it's not present
dict.keys() - Returns a sequence containing the keys in the dictionary
dict.values() - Returns a sequence containing the values in the dictionary
dict.update(other_dictionary) - Updates the dictionary with the items coming from the other dictionary. - Existing entries will be replaced; new entries will be added.
dict.clear() - Removes all the items of the dictionary

files = {"jpg": 10, "csv": 25}

files["jpg"]
# 結果是 10

"jpg" in files
# 結果是 True，因為 file 內有 jpg

Dictionaries is mutable 更改

toc = {"Introduction":1, "Chapter 1":4, "Chapter 2":11, "Chapter 3":25, "Chapter 4":30}

toc["Chapter 5"] = 50
# 新增 Chapter 5

del toc["Chapter 4"]
# 刪除 Chapter 4

























































































# EXAMPLE 1
cool_beasts = {"octopuses":"tentacles", "dolphins":"fins", "rhinos":"horns"}
for key, value in cool_beasts.items():
    print("{} have {}".format(key, value))
    
#result
# octopuses have tentacles
# dolphins have fins
# rhinos have horns


#EXAMPLE 2
wardrobe = {"shirt":["red","blue","white"], "jeans":["blue","black"]}

for item, color in wardrobe.items():
	for color in color:
		print("{} {}".format(color, item))
        
# result
# red shirt
# blue shirt
# white shirt
# blue jeans
# black jeans


#EXAMPLE 3
def email_list(domains):
	emails = []
	for mail, users in domains.items():
	  for user in users:
	    emails.append(user + "@" + mail)
	return(emails)

print(email_list({"gmail.com": ["clark.kent", "diana.prince", "peter.parker"], "yahoo.com": ["barbara.gordon", "jean.grey"], "hotmail.com": ["bruce.wayne"]}))

#result
# ['clark.kent@gmail.com', 'diana.prince@gmail.com', 'peter.parker@gmail.com', 'barbara.gordon@yahoo.com', 'jean.grey@yahoo.com', 'bruce.wayne@hotmail.com']


#EXAMPLE 4

def groups_per_user(group_dictionary):
    user_groups = {}
    # Go through group_dictionary
    for groups, users in group_dictionary.items():
        # Now go through the users in the group
        for user in users:
            ### Now add the group to the the list of
            ### groups for this user, creating the entry
            ### in the dictionary if necessary
            # if user is exist in user_goups, append to 
            # the list. At first it does not exist so
            # it goes else part.
            if user in user_groups:
                user_groups[user].append(groups)
            # if user not exist it is create the firts
            # key:value pair.
            else:
                user_groups[user] = [groups]

    return(user_groups)

print(groups_per_user({"local": ["admin", "userA"],
        "public":  ["admin", "userB"],
        "administrator": ["admin"] }))
        
#result
# {'admin': ['local', 'public', 'administrator'], 'userA': ['local'], 'userB': ['public']}


#EXAMPLE 5

def combine_guests(guests1, guests2):
  # Combine both dictionaries into one, with each key listed 
  # only once, and the value from guests1 taking precedence
  guests2.update(guests1)
  return guests2

Rorys_guests = { "Adam":2, "Brenda":3, "David":1, "Jose":3, "Charlotte":2, "Terry":1, "Robert":4}
Taylors_guests = { "David":4, "Nancy":1, "Robert":2, "Adam":1, "Samantha":3, "Chris":5}

print(combine_guests(Rorys_guests, Taylors_guests))

#result
# {'David': 1, 'Nancy': 1, 'Robert': 4, 'Adam': 2, 'Samantha': 3, 'Chris': 5, 'Brenda': 3, 'Jose': 3, 'Charlotte': 2, 'Terry': 1}

Variables

length = 10
width = 2
area = length * width
print(area)

length, width, area are variables
- assignment
- expression
variable 命名限制
- 不能使用 Python 內建的關鍵字或 function 名稱
- 不能使用空白格
- 必須以字母或_當開頭
- 只能以 字母、_ 與 數字 組成變數名稱

Type Conversion

implicit conversion

print("I " + "like " + "Python.")

explicit conversion

base = 6
height = 3
area = (base*height)/2
print("The area of the triangle is: " + str(area))  # str()將數字轉換成 string

Function

function name = greeting
paremeter = name
body(action)

def greeting(name):
    print("Welcome, " + name)

Value

return value

def area(base, height):
    return base*height/2
    
# 這種寫法可以儲存變數
#> area_a = area(5, 4)
#> area_b = area(7, 3)
#> sum = area_a + area_b
#> print("Sum of both areas is " + str(sum))

call value

def greeting(name):
    print("welcome, " + name)
    
    
# 給予變數就能 call value
result = greeting("Christine")

# call 一次後再 print 會顯示 none，表示 return nothing

Condition

# This function compares two numbers and returns them
# in increasing order.
def order_numbers(number1, number2):
	if number2 > number1:
		return number1, number2
	else:
		return number2, number1

# 1) Fill in the blanks so the print statement displays the result
#    of the function call
smaller, bigger = order_numbers(100, 99)  # 變數的順序沒差
print(smaller, bigger)

#> 99 100

*練習題

def calculate_storage(filesize):
    block_size = 4096
    # Use floor division to calculate how many blocks are fully occupied
    full_blocks = filesize // block_size
    # Use the modulo operator to check whether there's any remainder
    partial_block_remainder = filesize % block_size
    # Depending on whether there's a remainder or not, return the right number.
    if partial_block_remainder > 0:
        return block_size*(full_blocks+1)
    return block_size

print(calculate_storage(1))    # Should be 4096
print(calculate_storage(4096)) # Should be 4096
print(calculate_storage(4097)) # Should be 8192
print(calculate_storage(6000)) # Should be 8192

Loops

While Loops

寫 Loop 該注意的事項

確認variables 是否都被定義了

確認是否有 break 的條件

x = 0
while x < 5:
    print("Not yet, the number is " + str(x))
    x = x + 1
print("x = " + str(x))

# EXAMPLE 1
def attempts(n):
    x = 1
    while x <= n:
        print("Attempt " + str(x))
        x += 1
    print("Done")
    
attempts(5)
#>Attepmt 1
#>Attepmt 2
#>Attepmt 3
#>Attepmt 4
#>Attepmt 5
#>Done


# EXAMPLE 2
def digits(n):
	count = 0
	if n == 0:
	  count = 1
	while (n >= 1):
		count += 1
		n = n/10
	return count
	
print(digits(25))   # Should print 2
print(digits(144))  # Should print 3
print(digits(1000)) # Should print 4
print(digits(0))    # Should print 1

#result
# 2
# 3
# 4
# 1

common errors in Loops: initialize the variables

忘了先定義 variable

# 錯誤寫法
def count_down(start_number):
  while (current > 0):
    print(current)
    current -= 1
  print("Zero!")

count_down(3)


# 正確寫法：有 initialize variable
def count_down(start_number):
  current = start_number  # 在這裡 initialize 'current' 這個變數為 'start_number'
  while (current > 0):
    print(current)
    current -= 1
  print("Zero!")

count_down(3)

以 Loop 做質因數分解

以下程式能找出組成 number 的所有質因數。
例如：number = 100，其質因數是 2, 2, 5, 5，因為 2x2x5x5 = 100。

def print_prime_factors(number):
  # Start with two, which is the first prime
  factor = 2
  # Keep going until the factor is larger than the number
  while factor <= number:
    # Check if factor is a divisor of number
    if number % factor == 0:
      # If it is, print it and divide the original number
      print(factor)
      number = number / factor
    else:
      # If it's not, increment the factor by one
      factor += 1
  return "Done"

print_prime_factors(100)
# Should print 2,2,5,5

n 是否為 2 的次方？

檢查 n 是否能被 2 整除
- 若能被 2 整除
  - 讓 n 再除以 2（排除 6, 10 等非 2 次方數字）
  - 若 n 除以 2 之後的數字，能被 2 整除，且 n 不等於 0
    - 返回 True
    - 否則返回 False

def is_power_of_two(n):
  while n % 2 == 0:
    n = n / 2
    if n % 2 ==0 and n !=0:
      return True
    return False
  # 例外狀況： 當 n = 2 時，n/2 =1 導致上述條件無法篩出 2
  if n == 1:
    return True
  return False
  

print(is_power_of_two(0)) # Should be False
print(is_power_of_two(1)) # Should be True
print(is_power_of_two(8)) # Should be True
print(is_power_of_two(9)) # Should be False

For Loop

for x in range(5):
    print(x)

range function
- start by 0
- a list of numbers will be less than the given value
x 會從 0 開始到 4，0, 1, 2, 3, 4，總共 5 個項目，最後一個 x 一定是 range 數字 - 1
examples



























































# EXAMPLE 1: do the number squared
def square(n):  # 平方的算法
    return n*n

def sum_squares(x): # 加總平方數
    sum = 0
    for n in range(x):
        sum += square(n)
    return sum

print(sum_square(10))  # should be 285


# EXAMPLE 2: print out the range as list length
friends = ['Taylor', 'Alex', 'Pat', 'Eli']
for friend in friends:
    print("Hi " + friend)
    
# EXAMPLE 3: length and sum
values = [23, 52, 59, 37, 48]
sum = 0
length = 0
for value in values:
    sum += value
    length += 1

print("Total sum: " + str(sum) + " - Average: " + str(sum/length))


# EXAMPLE 4
def votes(params):
	for vote in params:
	    print("Possible option:" + vote)

votes(["yes", "no", "maybe"])

#result
# Possible option:yes
# Possible option:no
# Possible option:maybe


# EXAMPLE 5
def multiplication_table(start, stop):
	for x in range(1, 4):
		for y in range(1, 4):
			print(str(x*y), end=" ")
		print()

multiplication_table(1, 3)
# Should print the multiplication table shown above

#result
# 1 2 3 
# 2 4 6 
# 3 6 9

`range()` 的用法

range(n): 0, 1, 2, … n-1
range(x,y): x, x+1, x+2, … y-1
range(p,q,r): p, p+r, p+2r, p+3r, … q-1 (if it's a valid increment)

# 設定特定的起始數字，不以 0 為起始數字
product = 1
for n in range(1, 10):
    product = product * n

print(product)


# 以 loop 計算階層，例如：4! = 1*2*3*4
def factorial(n):
    result = 1
    for i in range(1, n+1):
        result = result * i
    return result

print(factorial(4)) # 4! = 1*2*3*4, should return 24
print(factorial(5)) # 5! = 1*2*3*4*5, should return 120

# for loop 做 factorial
def factorial(n):
    result = 1
    for x in range(1, n+1):
        result = result * x
    return result

for n in range(10):
    print(n, factorial(n))

#result
# 0 1
# 1 1
# 2 2
# 3 6
# 4 24
# 5 120
# 6 720
# 7 5040
# 8 40320
# 9 362880


# range 的第三個 perameter
def to_celcius(x):
    return (x - 32)*5/9
    
for x in range(0, 101, 10):  #代表每 10 個循環一次
    print(x, to_celcius(x))

Nested For Loops

雙重循環的概念
Newline Character: end="" 能自動換行
在 for right in range(left, 7): 會將 range 數字跑完。







































#EXAMPLE 1
for left in range(7):
    for right in range(left, 7):
        print("[" + str(left) + "|" + str(right) + "]", end="")
        
    print()
    
#result
# [0|0][0|1][0|2][0|3][0|4][0|5][0|6]
# [1|1][1|2][1|3][1|4][1|5][1|6]
# [2|2][2|3][2|4][2|5][2|6]
# [3|3][3|4][3|5][3|6]
# [4|4][4|5][4|6]
# [5|5][5|6]
# [6|6]

#EXAMPLE 2
teams = ['Lakers', 'Warriors', 'Rocket', 'Celtics']

for home_teams in teams:
    for away_teams in teams:
        if home_teams != away_teams:
            print(home_teams + " VS " + away_teams)
            
#Result
# Lakers VS Warriors
# Lakers VS Rocket
# Lakers VS Celtics
# Warriors VS Lakers
# Warriors VS Rocket
# Warriors VS Celtics
# Rocket VS Lakers
# Rocket VS Warriors
# Rocket VS Celtics
# Celtics VS Lakers
# Celtics VS Warriors
# Celtics VS Rocket

for loops 的自動化應用

copy files to machines
process the contents of files
automatically install software

各種 Loop 的使用時機

for loops 適合有列表元素的任務
while loops 適合有條件式的重複性任務

Recursion

Recursion is common in soft-ware but rare in automation.
Recursion is the repeated application of the same procedure to a smaller problem,
can tackle complex problems by reducing to a simpler one.
會有一個 base-case 設定最低值，運作方式會從 base-case 開始，一直累計到 n
會在 function recall 自己
適合用在有多層套疊的情境（例如俄羅斯娃娃、多層資料夾）


# 典型的 Recursion 寫法
def recursive_function(parameters):
    if base_case_condition(parameters):
        return base_case_value
    recursive_function(modified_parameters)


#EXAMPLE 1
def fatorial(n):
    if n < 2:
        return 1
    return n * fatorial(n-1)
#result: 1*2*3*4*.....*n
# 也能寫成
def fact(n):
...     if n >= 1:
...             return n * fact(n-1)
...     return 1
...
>>> fact(4)
24


#EXAMPLE 2
def sum_positive_numbers(n):
    # The base case is n being smaller than 1
    if n < 1:
        return 0
    # The recursive case is adding this number to 
    # the sum of the numbers smaller than this one.
    return n + sum_positive_numbers(n-1)

print(sum_positive_numbers(3)) # Should be 6 因為 1+2+3
print(sum_positive_numbers(5)) # Should be 15 因為 1+2+3+4+5

Recursive 使用情境

適合：active directory, LDAP
不適合：超過 1000 次執行次數的項目，就無法使用